[NASA Gravity Assist] Searching for Life

[Orionid]

Gravity Assist: Deep Oceans in Deep Space, with Morgan Cable (2)


Morgan Cable is an astrobiologist at NASA’s Jet Propulsion Laboratory who studies the ocean moons of the solar system. In this photo she stands in front of a model of Saturn’s moon Enceladus. Credits: NASA

Jim Green: Well, one of the moons of Jupiter I've always been fascinated with is Europa. And that of course is an ocean world. We know that it has a large amount of water, maybe twice the amount of water Earth has below its icy crust. So how are Europa and Enceladus so much alike?

Morgan Cable: So yeah, Europa is another really fascinating place that I'm really passionate about exploring. Europa and Enceladus share a lot of similarities. They both seem to have these global liquid subsurface water oceans, liquid water oceans underneath an icy crust. They also seem to have, we know for Enceladus for sure has hydrothermal activity. So that means that down at the sea floor, there seem to be places where liquid water is interacting with hot rock, temperatures of boiling point of water, 100 degrees C or above. And that's really exciting for potential for life because here on Earth at our sea floor, we find these rich communities of life that exist, not just bacteria, but crabs, tube worms, multicellular life, all existing off of geothermal energy. And we think that the same thing may be happening on Europa as well. And so these moons seem to share these characteristics of having liquid water, chemistry and energy, the three ingredients for life as we know it.

Jim Green: Well, how is Europa and Enceladus so different?

Morgan Cable: They do share some differences which means that we need to explore both of them in my opinion with dedicated missions at some point. So Europa is much larger than Enceladus and so we can explore differences in how energy is distributed in these oceans over time. Enceladus' crust is a little bit thinner and we know that there are active plumes on Enceladus. We have tantalizing evidence for maybe some plume activity on Europa, too. And boy, wouldn't it be nice if a mission was going to go and look for that?

Jim Green: And that mission's coming up.

Morgan Cable: Yes! It is!

Jim Green: Yes! What's the name of that mission?

Morgan Cable: That mission is Europa Clipper. We're so excited that we'll be sending this amazing payload of instruments to go and explore all aspects of Europa doing flybys. So we'll be orbiting around Jupiter and we'll map the entire surface. We have instruments that can tell us what that surface is made of, whether it's organics or salts or ice or a combination of them. We have some instruments that will essentially be able to stick out their tongue and taste some of the particles that are being sputtered off the surface. So we'll be able to get composition without having to land. It's going to be fascinating. We'll be exploring how habitable the Europan environment could be and hopefully get a lot of hints about more information of what that ocean is like.

Morgan Cable: There are some theories that since there seems to be an abundance of electrons, we think down, at the ocean core interface, so where the ocean meets the rock and there seems to be a lack of electrons, we think at the ice ocean interface. That may mean that all of Europa, its whole ocean could act like a giant battery. And this is exciting for life because a lot of organisms can basically just take those electrons and move them from one place to the other and put a little energy tax on there so they can survive. But that can be a great way for an ecosystem to live. And so we're hoping to explore some of those possibilities with the Europa Clipper mission.

Jim Green: Yeah. In fact, Europa is about the size of our own moon. Now when you think about it, if a crack opens up and a wall of water comes spurting out, the gravity of Europa is so great that most of that material, maybe 99.9%, of it will fall back to the moon. So we don't anticipate these plumes to get very high, but we do expect them to be there and we want Europa Clipper flying through them.

Jim Green: Now, you've been doing a lot of field work and getting out and doing a variety of chemical analysis. So can you tell us about some of your favorite moments out in the field?

Morgan Cable: Oh gosh. Okay. There are two. My all-time favorite field work experience actually happened when I was a graduate student. I was lucky enough as a grad student at Cal Tech, I had two advisors, one at Cal Tech and one at JPL. And because of that partnership, I was able to go on a field expedition to the top of Mount Kilimanjaro as a grad student. And it was just amazing. So the reason Kilimanjaro is interesting is because at the very top is a glacier, is an ice field. And this glacier has been around, we think for about 10,000 years. And over that 10,000 year cycle, it actually grows and then recedes, grows and then recedes. And so it's melting now and it's exposing ice that probably hasn't been exposed for thousands of years. And so our mission was to go and hack into that ice and collect some samples and see if we could understand the kinds of life that were trapped inside. Now, Kilimanjaro is really high. It's about 20,000 feet. It's 58 95 meters at the top.

Jim Green: Wow.

Morgan Cable: And so some of the solar radiation that changes the ice can actually be a decent analog for some of these ice moons like Enceladus and Europa because there's less atmosphere between that ice and space. And so that was a really fascinating trip. Oh my gosh. The views from the top were just amazing. But my second field experience that I really loved doing is a partnership with a bunch of early career scientists and engineers. This has been funded through the PSTAR program, the planetary science and technology for astrobiology research. And we of course came up with a fancy acronym called FELDSPAR, which is a type of volcanic mineral. And the reason for that is because we were studying the volcanoes of Iceland. We'd been traveling to these fresh lava fields in Iceland.

Morgan Cable: It's one of the most volcanically active places in the entire world. And we've been searching for what kind of life colonizes a fresh lava field, what comes in first, what moves in next and we've been looking at this over time because these lava fields actually make great analogs for places like Mars to try to understand when you go and collect a sample such as Mars 2020 is going to do, the Perseverance rover is going to be caching some samples to bring back to Earth.

Jim Green: Wow, that's super. I wish I went with you on some of these trips. Well-

Morgan Cable: Oh, we would love to have you on, Jim.

Jim Green: Might take you up on that.

Jim Green: Okay. So Morgan, do you think we'll find life beyond Earth in your lifetime?

Morgan Cable:  Well, Jim, with all of the amazing instruments that we've been developing just over the last few years, we're finally at the point now where we have limits of detection such that if we were to land in the right spot with the right instrument, we could find life even if there were only trace amounts of it there. So I really do think that if we continue to support these missions to explore ocean worlds, that we'll find life in our lifetime.

Jim Green: All right, so I'm going to answer that question—

Morgan Cable: There we go.

Jim Green: By saying yes, and leave it to you to find it.

Morgan Cable: Yes, sir, Jim. We'll get right on that.

Jim Green: Well Morgan, I always like to ask my guests to tell me what was the event or person, place, activity or thing that got them so excited that they became the scientist they are today. And I call that event a gravity assist. So Morgan, what was your gravity assist?

Morgan Cable: Oh man, I have been lucky to have a lot of amazing mentors that have given me a boost, a gravity assist in my career. But there's one in particular that comes to mind. So I grew up in Florida, actually in Cape Canaveral, right next to Kennedy Space Center. And so I had rockets going off in my backyard all the time. And that inspired me.

Morgan Cable: In eighth grade, I did a science project about life on Mars and it was a great way to get my feet wet learning about planetary science. And during that time, I emailed a scientist who at that time worked at Arizona State University. His name was Dr. Ken Edgett. And now people may know him as one of the main scientists that works on the Mars hand lens imager MAHLI that's been on a bunch of our rovers, but I emailed him out of the blue as an eighth grader and was like, "Hello, I am interested in doing a science project."

Morgan Cable: And we struck up a correspondence. He ended up shipping me this giant box of a mineral called basalt that I could use for my experiments. And then I ended up actually getting to meet him later that year because that was the launch of Pathfinder. And so those of you who are good at math can look up and figure out how old I am based on this. But it was such an amazing thing that a scientist would take time out of their busy schedule to come and help me, this eighth grader, do my science project and that's what made me want to become a planetary scientist. And so I'm still good friends with Ken Edgett. Now we're both over here in California and it's just, it's neat to be able to look back on that.

Morgan Cable: And that's one of the things that's inspired me to do Gravity Assist for as many early career scientists. I run a space camp to help inspire people, young kids to go into science and engineering and it's just such a wonderful thing. And Jim, when you do a gravity assist, you actually steal a little bit of momentum from the body you're orbiting, but hopefully Ken Edgett didn't mind because it really was a tremendous help to me.

Jim Green Well Morgan, you have an enormous amount of momentum, so I want to thank you so much for a wonderful, delightful interview. It's just been a pleasure talking to you about some of those ocean worlds.

Morgan Cable: Well, Jim, thanks so much. It's been a real pleasure speaking to you and thanks for all that you do to make the missions that we get involved in possible and help expand our reaches and our senses out to the outer solar system and beyond.

Jim Green: Join me next time as we continue our journey to look for life beyond Earth. I'm Jim Green and this is your Gravity Assist.

Credits:
Lead producer: Elizabeth Landau
Audio engineer: Manny Cooper

Source: https://www.nasa.gov/mediacast/gravity-assist-deep-oceans-in-deep-space-with-morgan-cable/

[Adam.Przybyla]

... ten obrazek dobrze pasuje do tematu:
"Europa possesses a volume 2-3 times the volume of water in Earth's oceans"
Z powazaniem
                       Adam Przybyla
Zrodla:
https://twitter.com/Rainmaker1973/status/1364138182036578307

[Orionid]

Gravity Assist: There’s Life Under Ice in Antarctica. How About Mars? (1)
May 29, 2020

Climatic cycles of ice and dust build the Martian polar caps, season by season, year by year, and periodically whittle down their size when the climate changes. This image is a simulated 3-D perspective view, created from image data taken by the THEMIS instrument on NASA's Mars Odyssey spacecraft. Credits: NASA/JPL/Arizona State University, R. Luk

From diving in Antarctica’s ice-covered lakes to exploring Mexico’s Cave of the Crystals, NASA astrobiologist Chris McKay has been searching for life in a wide variety of extreme environments on Earth. He’s also working on an idea to send a probe called Icebreaker to the polar caps of Mars. Beyond merely finding life on another planet, he’s excited about the idea that potential life on a place like Titan, with a totally different chemistry than ours, could have arisen independently from life on Earth. Learn about Chris’s exciting fieldwork and the concept of life’s “second genesis” in this episode.

Jim Green: Did life have a single origin in the solar system? Or could there be life on Mars that came about totally independently from life here on Earth? And how would we know that?

Chris McKay: And that's one reason why I have a special love for Titan, because there's no way anything that lives in liquid methane is related to anybody you know.

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green: I'm here with Dr. Chris McKay and he is a planetary geologist at the NASA Ames Research Center. His current research focus is on the evolution of the solar system and the origin of life. Welcome Chris, to Gravity Assist.

Chris McKay: Glad to be here, Jim.

Jim Green: Well, you've had a long and distinguished career in astrobiology. Where do you think you would look out into the solar system as being the best places to find life beyond Earth?

Chris McKay: I think the places that we're most likely to find life beyond the Earth soon are Mars and Enceladus. And the reason is: those worlds have or had water, liquid water. We have clear evidence that there's organic material present, nutrients needed for life like nitrogen, and a source of energy that life can use. So all the big boxes are checked for those two places. So those are the places where I'm focusing my energies in terms of trying to do a mission to search for life.

Chris McKay: A couple of important points that we learned from Cassini about Enceladus is that in that water, in that ocean that's coming out into space, there are chemicals that are the sort of chemicals that many microorganisms use to get energy—so-called “redox couples,” for example, hydrogen and C02. Now that doesn't sound like dinner to us human beings, but some microorganisms just love to eat that stuff. So a source of biologically available energy is important. And also, life needs nitrogen. Fertilizer is basically nitrogen. And we see that in the plume too.

Chris McKay: So the Cassini results have just been outstanding. They have really revealed the interior of Enceladus by an analyzing the plume and shown us that that interior is habitable. It's very much like our own oceans. It's very tantalizing and there are samples coming out into space, it's almost too good to be true.

Chris McKay: I think the best thing to do next is fly through the plume. Now based on what we find there, we may decide we'd like to land or we'd even like to go diving into the ocean. But clearly the first step: fly through the plume, collect some material and see what it is.

Jim Green: Is the expectation that life would be microbial or something more complex?

Chris McKay: Well, the expectation is that it would be microbial for two reasons. One is when we look on Earth at environments like what we expect Enceladus, what we find there are microbial life. What are the kinds of organisms that eat hydrogen and CO2 and make methane? Well, they're microorganisms. The other reason is that we don't expect Enceladus to have oxygen in its ocean. And all large forms of life on Earth require oxygen. So what we're planning for and what we're developing instruments to look for is microbial life. Now, one of the things we've certainly learned from planetary science is: be surprised. One of the reasons I like the field is because we're often wrong and often surprised.

Jim Green: What about Europa? Is that a good place to go looking for life, or would you rather go to Enceladus?

Chris McKay: Well, I think we want to go to Europa. And what we need to do there, what we need to do at Europa is do what Cassini did it at Enceladus. Was…show that there's organics show that there's biologically available energy and show that there are nutrients like nitrogen containing compounds. We know that there's water, but we need to check those other boxes, too. And I think, and I'm hopeful that the Clipper mission which is being built and will go on its way, will do just that. So I think Clipper will be for Europa, or I hope, what Cassini did for Enceladus and really open up our eyes to what the potential is for life and how to go about searching for it.

Jim Green: So you know, Titan is also another exciting moon at Saturn. And what do you think about its opportunity to be able to harbor life?

Chris McKay: Well, Titan is in a category all by itself. All the other targets that we're working on for life are interesting because they have a liquid and that liquid is water. Or they had a liquid. Titan has a liquid. It's all over the surface. It's the only world that has beaches besides the Earth.

Chris McKay: But that liquid's not water. It's liquid methane. Now that is interesting and challenging. It's challenging because we have no idea how life could use liquid methane as a substitute for water. We can barely understand life with liquid water.

Chris McKay: But it's interesting because if we were to find life on Titan growing and liquid methane, that would tell us not only that life is widespread in the universe, but that it's really diverse. That it's weird. There are weird forms of life. With just Titan and Earth, we don't know who's the weird one, is it them or us? But it tells us that the universe is full of life and it's full of diverse life. To me that is the best possible outcome of our exploration. That we go to Titan, we find life, and we find it is so different that it's clearly a second genesis.

Jim Green: Chris, when you talk about a second genesis, what exactly do you really mean and what would it look like?

Chris McKay: Well, we can say clearly what we mean by a second genesis. We mean life that had a separate origin than life on Earth. The challenge is how would you recognize it? How would you know that it's different? That's really the hard part. And the answer that we've come up with so far is if we look at life on Earth, we see certain patterns that are completely and 100% universal to all life on Earth. For example, all life on Earth uses only lefthanded amino acids in the formation of its proteins. So all life uses proteins. And it only uses left-handed amino acids in those proteins, but proteins come in both right and left handedness. Life on Earth has chosen, on Earth, has chosen the left handedness.

Chris McKay: Suppose we go to Mars, we find molecules that we think are biological and contains a lot of amino acids and they're all righthanded. I would argue that that is a persuasive evidence that that life form is completely different than life on Earth. That it drives on the other side of the road. And that is such a fundamental difference in biochemistry that it has to represent a separate origin and a separate evolutionary path. There may be more, and it may be a combination of many things like this that tells us that, yeah, this has similar biomolecules in us, but it represents a completely different way of encoding that information. It really is a second genesis.

Chris McKay: And that's one reason why I have a special love for Titan, because there's no way anything that lives in liquid methane is related to anybody you know.

Jim Green: Right.

Jim Green: We have what I would call a lot of circumstantial evidence that there may be life out there, but until we get it here, get it in our laboratories and can really examine it in many different ways with many different tools, we're not necessarily going to be sure. We also are about ready to launch the Perseverance rover along with its helicopter Ingenuity to Mars. They're going to be creating samples and we are going to bring those samples back. So we'll have an opportunity to look for life in the rock record. But there are other places on Mars that we ought to be going. There's things that we ought to be doing. What is the next best idea to be able to look for life on Mars?

Chris McKay: Well, one of the missions that I've been looking at, and I'm interested in is landing in the polar regions and drilling down to the ice on Earth in the polar regions. And I've specialized in the polar regions. I like it cold. In the polar regions. We find that ice is very good at preserving the biomolecules that life is made out of. So there we might find not just evidence of life, not just fossils, but the actual frozen remains of biomolecules. Think of the wooly mammoths in Siberia, frozen and preserved in ice. We want the microscopic ancient equivalent of those on Mars. And so going to the polar regions I think has, is very attractive from a scientific point of view. It's very challenging from a technical point of view, because you don't have long, the summer's not very long. Sunlight's not very bright.

Jim Green: Well you know the ice on the Mars polar cap, when we look at the spectrum of reflected light it tells us it's CO2, but isn't that just a veneer and don't we believe that there's an enormous amount of water trapped underneath that veneer of CO2?

Chris McKay: That's correct. That's correct. And if we look at the permafrost areas where there's ice cemented ground, for example, at the Phoenix site where Phoenix landed in 2007 it's 68 degrees North. That is clearly ice cemented ground just a little bit below the surface. And that's water ice. And the interesting thing is at that site, a few million years ago when Mars was tilted more in its orbit, that ice could have been that ice cemented ground could have been muddy like the Arctic on Earth becomes in the summertime.

Jim Green: Oh wow. Yeah, I didn't think of that. But you're right. Yeah. So we really need some sort of ice interrogator mission to, to go back there and take a look at it.

Chris McKay: Right, right. And drilling through ice is very hard. Think of it as concrete. It's dirt and ice cemented together. It's very difficult to drill through. It's hard enough doing it on Earth, it's very challenging on Mars. That's the technology hurdle that we're focusing on is drilling into the ice. We call our mission Icebreaker for that reason.

Jim Green: Well indeed, as you say, drilling here on Earth, those are those locations on Earth for which they're much like that which would be at Mars, gives you the opportunity to test your instruments. So what exotic locations have you gone to be able to do these tests and the field work here on Earth?

Chris McKay: Well that for the Phoenix site, for the Mars polar regions, the best analog, the site on Earth that is my favorite spot for testing instruments and technologies like the drill, are the high valleys of the dry valleys of Antarctica. These are very cold and very dry. When we think of Antarctica, most people think huge ice sheets and glaciers. Well listen, if you standing in the upper valleys of the dry valleys, it looks barren. There's rocks and dirt. There's very little ice.

Chris McKay: We have to hike to find water to get drinking water, but that is a good Mars analog for the Mars polar regions. It is the coldest desert, dry desert location on Earth and like on Mars the surface is dry, but underneath the surface there is ice cemented ground. We dig down to that ice cemented ground and we are doing the closest parallel on Earth to what we will hope to do on Mars. When we go back to the Phoenix site, that area and drill down and get into the ice instead of just reaching it, get into it.

Chris McKay: And what we're finding in these high valleys is, it's pretty tough for life there and we're still working it, but it seems like that's very close to the limit of what life can do in terms of cold and dry. And so it's really, it's at the edge of exploration. Is this a place where life can survive at all? A lot of extreme environments, we go there and yeah, it's extreme, but it's just full of life, right? Think of salt ponds, extreme salinity, purple with life, pink with life. Think of deep sea vents, very hot but full of life. Here we're finding extreme environments where life, all forms of life, find it extreme. And so it's a challenge. We don't yet have the answer. Is this telling us that there could be life in the permafrost of Mars, or is it not?

[Orionid]

Gravity Assist: There’s Life Under Ice in Antarctica. How About Mars? (2)


Chris McKay in Antarctica. Credits: Chris McKay

Jim Green: Well, one of the things about that as you point out is because the axis has changed over time. It's called the obliquity of the planet. We're finding that in different locations would have been more temperate, so indeed maybe that ice was water. And then here on Earth where we go, where we find water, as you point out, you find life. So that may mean that maybe life is trapped in that ice so you have that opportunity even in the permafrost areas of Mars to find.

Chris McKay: Right.

Jim Green: Well you've been out on many field experiments and as you say, you're planning to go back to the dry valleys. Would you be able to do that this year? I mean the summer is coming up in the November timeframe. Is that the perfect time to go?

Chris McKay: That's right. We normally go to the Antarctic when it's summer down there and it's winter here and how that's going to work this year is unclear. Everything is right now in a state of flux. But if things in a sense return to normal in time, then we might be able to still do our field work. But in the big scope of things, we've been working in the Antarctic for many decades now. And so, if we miss a year, we miss a year.

Jim Green: What would you say is one of your more unusual experiences while you've been out in the field?

Chris McKay: Well, I would think that the most unusual experiences we've had in the field, two of them come to mind. One is in the Antarctic where we under the leadership of Dale Anderson, our PI in one of the projects, we dive into ice covered lakes. So imagine a layer of ice. It's almost 10 feet thick floating on top of a lake in a very cold remote environment. We drill a hole, a meter in diameter hole and we dive in and investigate the life at the bottom of that lake. It is really like entering into another world.

Jim Green: Ah!

Chris McKay: This environment is so isolated, so remote that there are no fish, there's no tadpoles, there's nothing swimming. If you didn't understand the microorganisms, you would think it was lifeless. But it's not. It's teeming with life. They're just microscopic. And the interesting thing we discovered is that in this lake in Antarctica, the microorganisms are building mounds that are about 10 or 20 centimeters high. And if you think of a microorganism that's a millionth of a millimeter, building a mound 10 centimeters high, that's [an] enormous scale difference between the things they built and the size of the organisms. It makes the pyramids look like an easy project.

Chris McKay: And these mounds, when the microorganisms die and the lake dries up, would be preserved, their organics would be preserved, the structures would be preserved and they represent potential evidence for what we might find for life on Mars or on the early Earth. So diving into that lake, the thing that I keep thinking is, this is like going back in time to the early Earth, three and a half billion years ago, when all that was here on Earth was microorganisms. And maybe at the same time it's like going to Mars and finding what life was like on Mars back when it was only microorganisms.

Chris McKay: The second similar experience is going into a remote cave underwater chamber in Mexico, called the cave of the crystals. Which was a huge room with giant crystals, the size of telephone poles that had formed over millions of years. Very hot, very humid. We needed protective suits just like we did in diving. So, the cold extreme in Antarctica and this other worldly environment of an ice-covered lake and the hot extreme in this crystal cave in Mexico…

Jim Green: Okay, so then when you got into the cave, what are those crystals look like?

Chris McKay: They look like chandeliers. Gigantic pieces from chandeliers that have fallen down all throughout the cave. And they have grown up slowly over millions of years.

Chris McKay: And the main reason I was in the cave was to further research and try to investigate things without touching them.

Jim Green: Hm!

Chris McKay: If you think back, this was 10 years ago before Curiosity and before the development of remote sensing instruments on rovers, we were just beginning to think, "How could we analyze something without picking it up, without touching it?"

Chris McKay: So I asked myself: Is there some way to analyze them, look for microorganisms and organics in the crystal without chipping anything off the crystal? Treating it like it was a work of art. Like it was the Mona Lisa and you wouldn't tear it up to analyze it. And so we went in there with a Raman spectrometer to see if we could characterize a mineralogy and look for organics and even biosignatures without sampling the crystal at all. And of course we could. It worked out very well, we were very pleased with the results. And this was part of the logic that led to the current focus on remote sensing instruments on rovers on Mars and so on. If we can sample things without touching them, it makes life on Mars a lot easier. And in this case in the crystal, there was a deeper motivation for wanting to do it.

Jim Green: Well many that do that have expressed the fact that they believe there's more biomass below our feet than there is on the surface of the Earth. Now when you think about it, that means that life has got a tremendous hold here on Earth. And if that happened at Mars, and even though the surface life may not exist anymore, we may find evidence of life below the surface. Do you think we'd find it in aquifers or, or in deep areas on Mars?

Chris McKay: That's a very important point. The subsurface may hold a larger biological signal than the surface on Earth and on Mars for sure. And so we need to look. Aquifers, any environment. I think our knowledge of the subsurface of Mars is so limited and our knowledge of how life spread on Mars is so limited that we have to take the approach: look everywhere, look wherever we can and everywhere we can. And if we find an aquifer, obviously that would be a hot place, very important place to go. Unfortunately, so far we haven't found a lot. There's some evidence of one underneath the polar regions, one of the polar caps, but searching for water is definitely the way to proceed.

Chris McKay: And if find subsurface water, if we find aquifers or if we find even ice that could have melted millions of years ago, or if we find high levels of hydrated minerals, those are all possible targets that we should investigate. I think we really should take the philosophy of: leave no stone unturned so to speak. It has a lot of stones. We should start unturning them.

Jim Green: Yeah, you're right. Yeah, because you never know what you're going to find underneath the stone. Yeah, indeed. Well, okay, let's say you find it. You spent a significant amount of your research life developing instruments capability, thinking about deeply what we should be looking for. Now you've come across it. What do you think will happen next? What would your reaction be and what do you think about the public's reaction? Are we ready for that discovery?

Chris McKay: My own answer to that question. My personal answer is we proceed very, very carefully. And the first thing we do is we remove from Mars all the spacecraft we've sent there, because they're all harbor Earth contamination at some level. We remove it. That contamination isn't growing, it hasn't altered Mars, but it's there with the potential to grow. These are dormant organisms that we know are inside all of our spacecraft. We remove them and then we think, what do we do? Do we still send humans to the surface? Do we leave Mars alone? Do we actively try to support and enhance the life that's there. Now being a advocate for life, I favor the latter. We study that life. And once we understand what it needs, we try to help it. We try to make it more like life on Earth, spreading all over, deeply rooted, extending over all parts of the planet. We try to encourage its own biosphere.

Jim Green: Carl Sagan always said that if we did find life on Mars, we need to leave it to the Martians. But you know, as you point out, and we know the evolution of Mars has been from a blue planet now to a much more an arid planet. And if life exists, perhaps below the surface, maybe it's in the waning era of its existence. And that's something we would want to investigate, think about, to determine what its future is along with ours.

Chris McKay: Right. And my approach would be we're from the government. We're here to help.

Jim Green: Well, you know Chris, I always like to ask my guests to tell me what was the event or person, place, or a thing that got them so excited about becoming the scientist they are today. And I call that a gravity assist. So Chris, what was your gravity assist?

Chris McKay: That's a good question, and the answer for me is very clear. It was coming to NASA Ames as a graduate student for a summer internship.

Chris McKay: They haven't been able to get rid of me since. That's where and when I decided that I was going to do astrobiology, although we didn't call it that then. That's where I got involved in the Antarctic work in the dry valleys. That's where I started working with Jim Pollack and Brian Toon and other really, well, famous planetary scientists. And trying to understand the link between planetary science and the origin of life. It started at that summer. That was an eight-week experience and that was my gravity assist that Delta V that I got from that gravity assist has been carrying me forward ever since.

Jim Green: Well that's fantastic. I really appreciate talking to you about some of these issues. You're really right at the forefront of all that research. So Chris, thank you so much for joining me today on Gravity Assist.

Chris McKay: You bet.

Jim Green: Join me next time as we continue our journey to look for life beyond Earth. I'm Jim Green and this is your Gravity Assist.

Credits: Lead producer: Elizabeth Landau

https://www.nasa.gov/mediacast/gravity-assist-there-s-life-under-ice-in-antarctica-how-about-mars

[Orionid]

Gravity Assist: Is Our Solar System Weird? With Shawn Domagal-Goldman (1)
Jun 5, 2020


Scientists are finding planetary systems beyond the Sun that are quite unlike our own.  Credits: NASA/JPL-Caltech

We now know there are more planets than stars in the galaxy. Many of them are very different from ours. How would we know if any of them had life? Shawn Domagal-Goldman, astrobiologist at NASA’s Goddard Space Flight Center, discusses these strange and wondrous worlds beyond our Sun. He and others at NASA are working on concepts for future space telescopes that could actually find exoplanets that resemble Earth, and detect chemicals that only life could produce. And what would such a discovery mean? Find out in this episode.

Jim Green: We now believe there are more planets in our galaxy than there are stars, completely changing our view of where life might exist. Let's talk to an expert. Is there life beyond Earth on an exoplanet?

Shawn Domagal-Goldman: And if I’m wrong, I’m wrong, but that’s what we do as scientists, right? We can do that now.

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green: I'm here with Dr. Shawn Domagal-Goldman. He's a research scientist and astrobiologist at NASA's Goddard Space Flight Center. Shawn studies rocky exoplanets, and he wants to know about a planet's surface climate, its habitability, and ecosystems. Welcome, Shawn.

Shawn Domagal-Goldman: Thanks for having me, Jim. I'm a fan of the pod.

Jim Green: Yeah, thank you. Well, you know the first planet another star was discovered in 1992. Now that's not too long ago. And we immediately called it an exoplanet, and started looking for more of them. What do we know today about exoplanets?

Shawn Domagal-Goldman: Well, the first, for me, is that they exist. Because when I was born, there were none. We had, at that point, nine planets in our Solar System, and nothing beyond it. They were an idea. There was something we had talked about finding one day. And starting in '92, we started finding them.

Shawn Domagal-Goldman: Now we know of literally thousands of them. And because we know of thousands of them, we also can start looking at them like a census almost, like how many planets of certain sizes are there, how many of certain orbits are there. And we're starting to learn a lot of surprising things. We're starting to learn a lot about how common Earth-like planets could be, although that Earth-like term is controversial. Basically, when we say that, how common are planets that are the size of Earth and get the same amount of energy from their host star that we get from the Sun.

Shawn Domagal-Goldman: So we can do that now. I can go out with my kid, look at the night sky, count stars, and tell her, that on average, there's a planet for every star.

Jim Green: Wow. You know—

Shawn Domagal-Goldman: You couldn't do that in '92.


NASA’s chief scientist Jim Green with astrobiologist Shawn Domagal-Goldman. Credits: NASA

Jim Green: That's right. You couldn't. In fact, I think what was inhibiting the astronomers prior to that, was the concept as well. The planets are so small, we'll never be able to detect them around a star, which as we see it, is just a point of light, and way far away.

Shawn Domagal-Goldman: Yes. So every detection method we have relies on seeing how that point of light from the star changes.

Jim Green: In some way.

Shawn Domagal-Goldman: In some way. Sometimes it dips, because the planet's in front of it. The analogy I give is it's like, if you're of my age, E.T. and Elliot, flying in front of the moon, and blocking a lot. Or if you're seeing an eclipse, the sunlight getting blocked, that when planets do that from far away, it just makes the star dim a tiny bit, and we can see that. Or, if the planet's tugging gravitationally on the star back and forth, we can actually see the motion of the star towards us and then away from us, and towards us and away from us. But you're right. No matter what we do today, with a couple exceptions, we're seeing the star's light change.

Shawn Domagal-Goldman: Eventually we want to see the planets themselves, because then now we can start to tease apart what the planets themselves are like. Not quite there yet.

Jim Green: Yeah. That's the next big step. Well, as you said, we've found thousands of planets now. They're confirmed, okay. And we now know there are more exoplanets in our galaxy than there are stars, which is another spectacular concept. Well what type of planets are they? And does every planet in our Solar System have a counterpart?

Shawn Domagal-Goldman: Every planet in our Solar System has a counterpart. But we might be the Portland of solar systems. Like, we're weird, in that we don't have a couple things that we see commonly elsewhere. And that's actually thrown us for a couple of loops when we're interpreting the data.

Shawn Domagal-Goldman: The very first exoplanets we found, they're these things called Hot Jupiters. So they're bigger than Jupiter, but they're closer to their parents' star than Mercury is to the Sun. So they're really, really hot.

Jim Green: Yeah, and they could be on elliptical orbits.

Shawn Domagal-Goldman: They could be on elliptical orbits.

Jim Green: That was a really strange one.

Shawn Domagal-Goldman: It could be on a what's called inclined orbits. So if you ever see that old picture of an atom, where there's circles going in different directions. There's solar systems where the orbits are inclined like that. You could almost imagine a system, and it probably exists out there.

Shawn Domagal-Goldman: The Hot Jupiters we found first. We didn't know they were planets when we first saw them, because they were so foreign to our expectations. We had these predictions, there would be very few planets bigger than Earth, but smaller than Neptune and Uranus, because there's nothing in our Solar System of that size. But it turns out that planets of that size, they don't just exist, they're actually the most common size planet we found out there.

Shawn Domagal-Goldman: So for everything we have here, there is an analogy out there. But the opposite is not true. There's far more kinds of planets beyond our Solar System than we have in just our one example inside the Solar System, the ones that we have here.

Jim Green: Yeah. When this was really, early on, hot field and everyone was looking for exoplanets, I imagined that the planet that we'd find the most would be Jupiter-size planets. And that turns out not to be the case.

Shawn Domagal-Goldman: No. It ends up following what seems to be a sort of general rule of both stars and planets, that the smaller things tend to be more common. Although that may not be true down all the way to the Earth-size, but certainly down to the size of things slightly bigger than Earth. Those are more common than the really bigger things, like Jupiter and Saturn.

Shawn Domagal-Goldman: I should correct myself. There is one kind of thing we have here, that we haven't found elsewhere yet. And that's moons.

Jim Green: If we just are able to find a planet the size of the Earth around a star, and some Mercury-size planets around stars, finding moons has got to be a tough thing to do.

Jim Green: Well, what have we learned about our Solar System from studying exoplanets?

Shawn Domagal-Goldman: For me, I think, the lesson I've taken, is how our Solar has evolved, how the planets formed and changed their orbits over time. We thought, I think, when 20 years ago, before we found all these exoplanets, I think we had an image of the Solar System, I call it like a “peas and carrots.” You had the small stuff close in, and you had the big things back far away. And never shall the two mix.

Shawn Domagal-Goldman: But because we found these Hot Jupiters, these really big things close in, and we found some small things further away, we know that the evolution of these systems is much more dynamic than we ever imagined before. Knowing that, has informed our thinking of how our Solar System has evolved over time. People have taken improved models that can recreate those exoplanets and applied them to the Solar System.

Shawn Domagal-Goldman: And as a result, we can explain why Mars is the size it is, and has the orbit it does, much better, because now we think of these ideas of the gas giants moving in at one point in our Solar System's history, and then moving back out. It's that kind of thing.

Shawn Domagal-Goldman: We had a model. We had some physics. But we knew that the physics that caused that, was probably more common from having to use it to recreate the exoplanets. And then taking that back to the Solar System, we can tell a better story, a more comprehensive story of the planets back home, which I think is fascinating.

Jim Green: Yeah, it is. So let me flip that in asking, how has our study of the Earth and our Solar System informed us about exoplanets?

Shawn Domagal-Goldman: I think there's a couple ways. One is a very real practical way, in that we have been doing decades of research on Earth, on our climate. We've been doing decades of research on the planets in our Solar System. And that gives us techniques to use. It gives us specific models.

Shawn Domagal-Goldman: My research, when I look at exoplanets or try to simulate them, the origins of the chemistry code that I use, goes all the way back to us studying the ozone hole in the late '70s.

Shawn Domagal-Goldman: And we're using that today, 30, 40, 50 years later, to study these exoplanets. And we've had lots of specific development along the way, to make it really good at the exoplanet problem. But it wouldn't be possible if we hadn't been researching Earth, and Earth's chemistry, and Earth's climate, 40, 50 years ago.

Shawn Domagal-Goldman: The other way that it's really useful is, it gives us some framework when we look at these things. There's a reason we call large planets close into their stars “Hot Jupiters.” And there's a reason we call things between the size of Earth and Neptune “Super-Earths” or “Sub-Neptunes.” And scientists, sometimes we don't like those phrases, because they can, perhaps, be too evocative, be too specific to some people. But for me, and I think for a lot of people in the public, it is a foundation upon which we can build an idea or a concept.

Shawn Domagal-Goldman: So sometimes just the language, even though it can be confusing sometimes and controversial, it does give us a starting point to have a conversation, around what is that planet like? It's bigger than Earth, it's smaller than Neptune. And that foundation of experience that we have with the things closer to us can be really useful.

Jim Green: Right after we started finding exoplanets, another new concept came up. And this was all about, well, a star's light has got to be warming these objects. Where can we look in that exo-solar system, for planets that may actually harbor life? That term was called “habitable zone.” So how do we really define that today?

Shawn Domagal-Goldman: And folks, in the public, if you're listening to this, you may have also heard that as the Goldilocks zone. You're not too hot, you're not too cold, you're just right. It's mostly based on the idea that life as we know it needs water. And if we want to look for life on a planet around another star, ideally you'd want a lot of water.

Shawn Domagal-Goldman: And the reason you want a lot of water, is you want a lot of life, so that way it can give off a huge signal that we could see from across interstellar space, against the background of that really bright star that the planet's next to.

Shawn Domagal-Goldman: So we don't want just life eking out a living in ice cracks somewhere. We want a big global breathing biosphere that's going to give us a huge signal. And for that, what we really need is, like I said, a lot of water. So the science word for that is, we want liquid water surface oceans. So the habitable zone is all about the region around a star where liquid water surface oceans could exist. Because that's what we think we need to get a really big signal from the biosphere.

Jim Green: Well there's some real nuances in that.

Shawn Domagal-Goldman: Oh yeah.

Jim Green: In the sense that, when we look at our Solar System, we see Venus is too hot, Mars is too cold, the Earth must be in the habitable zone. But in reality, the Earth itself, with its climate, and with its atmosphere, is warming itself, through greenhouse gases. And in fact, it's warmed itself to 80 degrees more than it would be without those important elements. And so it's really in a habitable state, not necessarily in the habitable zone.

Shawn Domagal-Goldman: It changes over time. It's possible Venus once was habitable. We think there's evidence that Mars was, at once, habitable.

Shawn Domagal-Goldman: So there is, to borrow a Monty Python phrase, you can have an ex-habitable planet, where you might've had life before, but you don't have it now. And that's something again, we've learned from the studies of our planets in the Solar System. And it's probably true for these exoplanets.

Shawn Domagal-Goldman: There's probably planets out there that were not habitable, but might be today. Or are habitable today, but might not be in a million or a billion years.

Shawn Domagal-Goldman: There's one other thing I should mention here, which is that a professor of mine, when I was a graduate student, Richard Alley, who is an expert on glaciation, and how glaciers change over time here on earth. He said something at a talk he was giving once. He said, "If I can tell the story of carbon, I can tell the story of Earth's climate history." And I would actually expand that. If I can tell the story of carbon, I can tell the history of Mars, and Earth, and Venus, in terms of their climate history. And I can also tell you the story of which planets could or could not have life, and those liquid water surface oceans.

Shawn Domagal-Goldman: An understanding of carbon is so essential to a fundamental understanding of climate. I can tell all of these stories, and I can make predictions, and they can be right, and I can be a rigorous scientist if I'm allowed to tell the story of carbon. If I cannot tell the story of carbon, I cannot recreate Earth today, or Earth a billion years ago, or Venus, or Mars in their histories, or these exoplanets in their habitable zones. Carbon is really essential to climate, whether it's here or elsewhere.

Jim Green: Well taking that concept then into exoplanets, how might we identify life on those exoplanets?

Shawn Domagal-Goldman: That's hard. Because the biggest challenge we have is, right off the bat, is a technical one. These planets are orbiting stars that are a billion times brighter than the planets themselves. So imagine you're tracking a baseball, or a plane, or a bird in the sky, and it flies across the Sun. You get blinded.

Shawn Domagal-Goldman: As a scientist, I would say, the detectors, your eyeballs, are getting overwhelmed by the light from the star. The same thing will happen when we look for life on exoplanets. Because we want to block out the star light, just so we can see the light from the planet. And if we don't do that, we're going to get a billion photons from the star, just for that one precious photon from that pale blue dot.

Shawn Domagal-Goldman: And then once we do that, we've got an entirely different challenge, which is a scientific one, which is how do you take that one poetic pale blue dot, and say that it's alive, or that it's not. For that, we again actually look at the gases in the atmosphere. So we basically put that light through a prism. We get its different color constituents. We call it a spectrum. And then we look at that spectrum to see if it has gases that life produces. The ultimate test really, is whether or not that combination of gases is unique to life.

Jim Green: Yeah. So what are the combination of gases that we would observe in an exoplanet, that would convince you that there's a biosphere there?

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Gravity Assist: Is Our Solar System Weird? With Shawn Domagal-Goldman (2)


Shawn Domagal-Goldman studies exoplanets and technologies that could determine if they are habitable. Credits: Shawn Domagal-Goldman

Shawn Domagal-Goldman: So there's one combination in particular, that I would find very convincing, and most of my colleagues, I think, would as well. And that's oxygen or ozone, which comes from oxygen, as well as methane. And the reason that's a powerful combination is, those two gases tend to destroy each other, or lead to reactions that destroy each other.

Shawn Domagal-Goldman: The analogy I give to people is it's like college students and pizza. If you see college students and pizza in the same room, you can make a pretty good guess that there's a pizza restaurant nearby. The reason is college students eat pizza fast. And if you have pizza in the same room as college students, chances are somebody made a lot of pizza all at once, and brought it to the party.

Shawn Domagal-Goldman: And I can make a pizza. I can make a pretty good pizza actually, but I can't a whole bunch of pizzas to fill a room full of college students, all at once. So in other words, the production rate of the pizza required to keep it there in the room with the college students is so high, you know there's got to be a pizza restaurant nearby. And it's the same thing.

Jim Green: So what's happening then, is the oxygen and the methane get together so fast, the oxygen pops off the carbon, becomes carbon dioxide.

Shawn Domagal-Goldman: Right.

Jim Green: Okay. So then that destroys it. But if you find a lot of oxygen and you find a lot of methane, something must be producing it-

Shawn Domagal-Goldman: Yeah, fast.

Jim Green: And tells you that immediately.

Shawn Domagal-Goldman: And fast, yeah.

Jim Green: Because it's there.

Shawn Domagal-Goldman: Yep.

Shawn Domagal-Goldman: And so that combination, that oxygen and methane, we see that in our atmosphere. You can take a spacecraft in the outer Solar System, look back at Earth, you'll see it. You can look at the light bouncing off of Earth, and then off the Moon back to us, you see it. Oxygen and methane are here. We can detect them. And if someone was looking at us, that's how they would know there was life here.

Jim Green: Well, one of the really exciting set of measurements that are being made on Mars is indeed, we see very small traces of methane, but we're also seeing small traces of oxygen, and that's a new observation. That's really tantalizing.

Shawn Domagal-Goldman: Yeah. My colleague, Melissa Trainer, here at Goddard, was a big part of that. And this is one of those things. When we find the unexpected, it really pushes us to think really hard about what's going on there? And when we answer that question, that's when you learn something. And that's what makes this fun.

Jim Green: Well what missions are being thought about that could actually make those observations in the future?

Shawn Domagal-Goldman: So the first one, and the one that I'm most excited about in the near term, is the James Webb Space Telescope.

Jim Green: Well that's a real telescope. That's going to happen.

Shawn Domagal-Goldman: That's going to happen next year.

Shawn Domagal-Goldman: To be honest, we're not expecting it to seek out signatures for all kinds of reasons. The types of exoplanets it's going to look at are around these really violent stars that might blow away the atmospheres of the planets.

Shawn Domagal-Goldman: Even if we get some atmospheres that we see, having the sensitivity to look for these biosignature gases, is going to be a really tall order for Webb.

Jim Green: Plus it looks primarily at the really big planets.

Shawn Domagal-Goldman:

And it's going to spend most of its time looking at the bigger planets. There's an outside chance, so I can't rule it out. But I'm not expecting it.

Shawn Domagal-Goldman: Longer term, I think our chances are better. Because this is such a hard measurement. I mean, this is part of what we do at NASA. We take a really hard challenge, and then we bring together really brilliant people on the engineering side, on the project management side, on the budget side, and we say, "How do we make this a reality?" And that for this, for this really hard question, I think we really need to start with the question, do these planets have biosignatures, and then design the mission around that.

Shawn Domagal-Goldman: We've got two concept missions. And that word, concept, is really important to focus on, because it means they're not funded, they're not things that have a specific launch date. They are things that are being considered by the scientific community at this stage.

Jim Green: Well that's necessary to do, because you have to be able to figure out what it would be like if we built a mission to do this.

Shawn Domagal-Goldman: Yeah, we need to know, is a mission that looks, on signs of life, on planets around other stars, is that a unicorn, or is that a thing we know how to build?

Shawn Domagal-Goldman: And finding out how many technologies we need, and how hard that's going to be. And if we got those, how long and how much money the mission might take to execute. Just so folks know, the two concepts I'm talking about are LUVOIR, which stands for the Large Ultraviolet Optical Infrared Telescope, and HabEx, which stands for the Habitable Exoplanet Imager, or Observatory.

Shawn Domagal-Goldman: Both of those missions would try to do this thing, where they block out the star light, get the pale blue dot, and then see if that pale blue dot has the gases that would constitute a biosignature.

Shawn Domagal-Goldman: With HabEx, what we're talking about doing is, we'd like to find at least one pale blue dot, have a high level of confidence we'll find one pale blue dot. And then roll the dice, and see what we see there.

Shawn Domagal-Goldman: With LUVOIR, we want to find up to 50, at the most ambitious versions of LUVOIR, 50 pale blue dots. And then start to do some systematic surveys of, how many of those planets have oceans? How many of those 50 pale blue dots have signs of life? And we can start to do statistics, and not just say, is life here on this one world, but how common is life in the universe?

Jim Green: Well, shouldn't we be thinking outside the box, and looking for signs of life that are very different than what we know about, in terms of our own life?

Shawn Domagal-Goldman: Yeah. This is one of the questions that I get so often. If you've watched Star Trek, or Star Wars, or any scifi, you see these fantastical things, and then you come to a scientist like me, and I say, "Well I'm going to look for oxygen and methane, because that's what we have on Earth." It's a tricky balance to play.

Shawn Domagal-Goldman: What we're trying to do is, we're trying to say, why is there oxygen and methane on Earth? And Earth was different at one point in the past, and it had life, and it didn't have oxygen or methane. So one thing, I think you're talking to Giada Arney later this season. One thing her and I have been working on, is we've been trying to think of what would biosignatures look like back on Earth when there was no oxygen, but there was still life. That would have been, what we call an alien biosphere, here on Earth, that we have recorded in the rock record. So we start with that.

Shawn Domagal-Goldman: And then from that, we start to tease apart, almost like a fundamental theory of biology. If I gave you as a planet, a certain combination of gases and a certain kind of energy source, what would the biology on that planet do? I say, we have to think like the planet, or think like the bacteria on that planet, what's the best strategy for getting energy in that planet? And what would you make as a byproduct for getting that energy? And we look for that. So that's the very generic version, or the general version that would be less tied to Earth.

Shawn Domagal-Goldman: But that's also a model we don't have. It's just a model in my head, and in my colleagues' heads, that we can talk about on a podcast. But we don't have that numerical model yet that we could use. But we will have it by the time we fly the mission. But we don't have that today. That's cutting-edge research we're working on.

Jim Green: Well everything we've been talking about, with these telescopes really interrogating planets, are all focusing on that search for life question. But let me ask you this. If we don't find anything after searching with these telescopes, that indicate that these planets have life, what does that mean?

Shawn Domagal-Goldman: For me, this is what makes the search for life so much fun, because it's profound, no matter what the result is. If we find life out there, that changes our view of ourselves and our place in the cosmos. But I think that's also true if we don't find anything.

Jim Green: I do too.

Shawn Domagal-Goldman: I mean, if we found that we were the only example of a biosphere out there, how precious is what we have here, and what does that mean for how we operate in our day-to-day lives going forward? I think we'd have profound impacts either way.

Jim Green: I do too, because to me, that would indicate, if we don't find life like us at all, after many decades of searching, that maybe complex life like us ends up dying quickly, from a human perspective, is a sad thing to think about. But I would want to know that. I would want to use that in thinking of how we would change that paradigm, that we, as a species, could do that, because we have the ability to do that. And we don't let what happens destroy us.

Shawn Domagal-Goldman: Well that's part of where this becomes fun. Because we're talking about exposing these questions to the scientific method, which means that we won't stop at a certain point. So if we found there was nothing, what you're getting at, is, we'd ask why.

Jim Green: Yeah. That's right.

Shawn Domagal-Goldman: Why is there no life out there? And we'd learn from that.

Shawn Domagal-Goldman: The other part of this is, I am expecting, I cannot wait for all my models to be wrong, about why there is or is not life and what kind of life is out there, because that's where we're going to learn something about the interaction between a planet and its biosphere. And as you were saying, knowing that is going to change how we operate back here at home, and I can't wait for that.

Jim Green: Yeah. I think so too. Well, okay, let me ask you this. Do you think we are alone in the galaxy?

Shawn Domagal-Goldman: I don't, but more importantly, I'm going to prove it.

Jim Green: Wow, cool.

Shawn Domagal-Goldman:

That's what's cool, right?

Jim Green: Yeah. That's right.

Shawn Domagal-Goldman: We're going to go out, and we're going to search. And if I'm wrong, I'm wrong. But that's what we do as scientists. And we can do that now.

Jim Green: That's right. So, okay. With that perspective, will we find evidence of life beyond Earth first in our Solar System, before we find it in exoplanets, or the reverse? What's your thought on that?

Shawn Domagal-Goldman: That's a tough one. What I'm doing right now, is I'm laying out the mission timelines on a chart almost. I think we'll find life outside. I think we'll find evidence of life outside the Solar System first. But I think we'll be convinced that we found life inside the Solar System first. In other words, I think we'll get the first paper saying, "Oh, I found something there, beyond the Solar System," before we have that here in the Solar System. But I think the rigorous proof that will convince the full scientific community will come from inside the Solar System for this.

Jim Green: All right, so you personally, how would you react to the discovery of life?

Shawn Domagal-Goldman: Am I on the paper?

Jim Green: Well, if you are, then you're going to defend it.

Shawn Domagal-Goldman: Yeah. If I'm on the paper, I'm probably popping a champagne bottle, and taking a long vacation. I mean, the immediate reaction, if I'm not on the paper, so I'm going to be taking a good hard look at it. I think if you're trying to get at how I'd react once I'm convinced, whether I'm on the paper or not. If I'm on the paper, I guess this moment would just happen earlier, when I've convinced myself that the data are there. I think my first reaction would be kind of a sense of relief, just because a lot of my career is oriented around this search, and this is—

Jim Green: A sense of accomplishment.

Shawn Domagal-Goldman: Accomplishment, even if it wasn't me, the fact that we did it, I would just feel relieved and satisfied. I'd probably plan a vacation, even if it wasn't my discovery. And then, it's so hard for me to break out of the thinking of a scientist. If I'm convinced, then I want to know, well what is that life like?

Jim Green: Yeah, it's the next level of detail that you're going to go into.

Shawn Domagal-Goldman: Yeah. On a more philosophical level, I think the other thing I'd start to think about is: how do we share this with the world? Because what I think would be more important to me is, if I was really convinced, I would want my neighbor to know about it, and them to be convinced and understand, from a scientific standpoint, what we're talking about. Because we're not talking about little green beings. Well, we're talking about tiny green, like we're talking about bacteria.

Jim Green: That's how it might start, yeah.

Shawn Domagal-Goldman: And I think getting to that point, with my neighbor coming up to me and telling me about it, that'd be, I guess, my next goal, is I'd want someone on the street to come up to me and tell me, "Hey, did you hear about what NASA did?" That's where I'd want to get to.

Jim Green: Well Shawn, I always like to ask my guests to tell me what was the person, place or thing that happened to them in their life, that got them so excited that they became a scientist, and they pursued intensely the field, in your case, of exoplanets. I call that a gravity assist. So, what was yours, Shawn?

Shawn Domagal-Goldman: My gravity assist was, I was in high school, and I was debating between whether I wanted to be a sports broadcaster, or some sort of academic. And I picked up a book called “The Case For Mars,” which was about sending humans to Mars one day. And that just, it blew me away. And the very end of that book, started to get into astrobiology, of this is part of what humans could do on Mars, is look for signs of life. And I thought that was, the idea that we could apply the scientific method to that question, it totally just got me focused on that.

Jim Green: Bob Zubrin.

Shawn Domagal-Goldman: Yeah, that's right.

Jim Green: Bob Zubrin.

Shawn Domagal-Goldman: So that really put me on a path towards really wanting to pursue astrobiology actually, as a career. And there was one faculty member at my university that was doing research on that a couple of years later. So that's what, Ariel Anbar, should give him a shout out here. That's what set me down this path.

Jim Green: Yeah, fantastic. Well Shawn, thanks so much for joining me in this Gravity Assist.

Shawn Domagal-Goldman:

Thank you. And you, on the gravity assist thing, you gave me a gravity assist too. Because then, fast forward, I came and worked for you, years later. And I learned a lot about, not just how science is done, but how we lead science communities, and lead projects and teams. And that's a big part of what we do at NASA too. And that's, I think, it really set me up for a successful career here at the agency.

Jim Green: Well, thank you very much, Shawn.

Shawn Domagal-Goldman: Yeah. Thank you, Jim.

Jim Green: My pleasure.

Shawn Domagal-Goldman: Yep.

Jim Green: Well join me next time as we continue our journey to look for life beyond Earth. I'm Jim Green, and this is your “Gravity Assist.”

Credits: Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper

Source: https://www.nasa.gov/mediacast/gravity-assist-is-our-solar-system-weird-with-shawn-domagal-goldman

[Orionid]

Gravity Assist: Puffy Planets, Powerful Telescopes, with Knicole Colon (1)
Jun 12, 2020


Knicole Colon, astrophysicist at NASA’s Goddard Space Flight Center, seen with the James Webb Space Telesocpe at Northrop Grumman Corporation in Redondo Beach, California. Credits: Knicole Colon

With more than 4,000 planets known that orbit other stars, scientists have discovered that many of these exoplanets are quite unlike our own. NASA has a whole fleet of spacecraft that look at different aspects of these planets. Currently TESS, the Transiting Exoplanet Survey Satellite, is checking out nearby stars for possible planets. It is helping to identify candidates that future telescopes will explore further. The upcoming James Webb Space Telescope will examine the atmospheres of exoplanets and look for clues about whether they are habitable. NASA astrophysicist Knicole Colon describes her work on the Kepler, Hubble, TESS and Webb missions, and takes us on a tour of some of her favorite planets. 

Jim Green: After James Webb gets launched, it's going to find all kinds of fantastic things and enhance our understanding of habitability. But what are the real measurements that it needs to make to tell us that these planets may be habitable?

Knicole Colon: Any information we can get is really going to help us move forward in pause our understanding of the universe, really.

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green: I'm here with Dr. Knicole Colon, and she's a research scientist, an astrophysicist at NASA's Goddard Space Flight Center, where she leads projects on the search for planets outside the solar system using the TESS space craft, and also planning for the upcoming James Webb Space Telescope. Welcome, Knicole, to Gravity Assist.

Knicole Colon: Thanks for having me


In 2011, NASA's Kepler mission discovered a planet called Kepler-16b where two suns set over the horizon instead of just one. It is informally called a "Tatooine-like" planet because Tatooine is the name of Luke Skywalker's home world in the science fiction movie Star Wars. But unlike in the film, Kepler-16b is not thought to be habitable. This is an illustration of Kepler-16b (shown in black) and its host stars. Credits: NASA/JPL-Caltech/R. Hurt

Jim Green: Knicole, why are you so excited about exoplanets in particular?

Knicole Colon: I love exoplanets. I love thinking about exoplanets and what they could be made of, what their surfaces could be like, what kind of clouds they have, what plant life they have. I think all of that is fascinating, because we have eight planets in our solar system, plus a lot of other small bodies, and now we know of thousands of exoplanets, so that's just a vast number, and so far they all seem really different, so that's why I'm excited constantly to learn more and more and more about them.

Jim Green: Well, you know, I grew up in the '60s, and we didn't really have a good view of the Earth until Apollo 8, when we saw the Earth rise above the moon, and it completely changed my world view to where I understood this was my home, and it is a planet, and it can be compared against the others, and it really changed my perspective. So, you've grown up with that perspective already.

Knicole Colon: That's right. I mean, I still was born before any exoplanets had been discovered, so I remember vaguely a time before exoplanets, but I definitely grew up knowing that it wasn't science fiction anymore. There really were exoplanets out there and we probably are not alone.

Jim Green: Right. And one of them might look like the beautiful blue marble we call Earth.

Jim Green: Well, we've used a variety of telescopes, and you in particular have used ground-based in addition to the space-based telescopes, both optical and near infrared to look for planets. You know, telescopes like the Kilodegree Extremely Little Telescope Transit Survey Telescope has really been used by you and your group. Can you tell me more about this ground-based telescope and what are you looking for?

Knicole Colon: Sure. The KELT Transit Survey is this really fun project I became involved in about seven years ago, and the goal of the survey was to find giant planets around bright stars, to understand just how common these types of planets are. Because we don't really have planets like these in our own solar system. These are planets that open within just a few days, so their year is a few days long, if you want to think about it like that. And with the KELT Survey, it's actually a really cute little telescope, hence the name, we said it's called the Kilodegree Extremely Little Telescope for a reason. It basically uses cameras with 42-millimeter, which is about 1.86-inch aperture, and it's looking for transits, which is really just measuring the brightness of stars and looking for periodic dips in their brightness.

Knicole Colon: And that dip tells us that there's a planet there around that star, and that we can see that from our point of view, all the way on Earth.

Jim Green: So, when did you start observing with this telescope, and how many planets have you found?

Knicole Colon: The KELT Survey in total has found 26 exoplanets. So, I joined the survey probably about halfway through, so it operated for about 14, 15 years.

Jim Green: Wow.

Knicole Colon: Yeah. It's quite a long journey, but actually it just recently shut down operations, and that was partly because of the success of the TESS Satellite, the all-sky Transiting Exoplanet Survey Satellite. So, KELT was really powerful in its heyday. But…

Jim Green: I see.

Knicole Colon: Now TESS kind of took over, but that's okay.

Jim Green: Well, before you got involved in TESS, you were involved in another spectacular exoplanet mission, and that was the Kepler space telescope.

Jim Green: In fact, Kepler lasted far longer than what we call its nominal mission, and it made all kinds of planet observations. Thousands of planets now. So, what discovery that Kepler made got you really excited? What was the most exciting discovery in your opinion?

Knicole Colon: Yeah. For me, I think I'd have to say it was the discovery of the first circumbinary planet. So, this was called Kepler-16b, and this is a planet that orbits around two stars. And to me, it's one thing to imagine that in science fiction, you know, in Star Wars, right?

Jim Green: That's right. Tatooine.

Knicole Colon: But to have direct evidence from the Kepler mission of such a planetary system was so exciting. And now we've discovered a bunch more circumbinary planets, so it's just all the more exciting.

Jim Green: Right. We shouldn't be. Yeah. We should expect the unexpected when it comes to these things. Yeah, absolutely. Well, you've also been a member of the Hubble Space Telescope science team. What were some of your activities with that team and how did you get involved with HST?

Knicole Colon: Yeah, so a couple years ago I ended up working... I moved from NASA Ames and working on Kepler to NASA Goddard, and again, the opportunity kind of fell in my lap to work on the Hubble team. Partly because I have an exoplanet background and the current team didn't have anyone with that particular expertise, so I was there to really do a lot of outreach, both in terms of the public and the scientific community. And first of all, let people know that Hubble was still going strong after 30 years in space for one, so that was a big part of it, but also just making sure that the scientific community had the resources they needed to collect and analyze data from Hubble. And with a particular mindset towards exoplanet science in my role.

Jim Green: Now you're involved in the TESS mission. Tell us more about TESS.

Knicole Colon: Yes. There's so many exciting missions right now. TESS is really... It's building on Kepler's legacy. So, Kepler discovered thousands of exoplanets, but TESS now, it's been up in space since 2018, so we just had the two-year anniversary of its launch, and in that time it's discovered also hundreds to actually over a thousand candidate planets right now as well, too. But the difference with Kepler is that it's discovering a lot of these planets around bright nearby stars, so stars that we can follow up then with other facilities, like Hubble, and really characterize these planets in detail and study their atmospheres.

Jim Green: So, indeed, Kepler looked at planets around stars that are very far away, and with the bright stars, which is what TESS is looking for, these are typically closer to the Earth. Are there any planets that are emerging from the TESS surveys that are exciting you?

Knicole Colon: Definitely. I may be a little biased here, but I will say one of the most exciting discoveries was one that a team I am part of made, and it's a three-planet system around a small star. But one of the planets is smaller than Earth, and it's just incredible that we're seeing that around these bright nearby stars, and they're already being studied with the Hubble telescope, as well, to start to get a glimpse of what their atmosphere may be composed of.

Jim Green: Well, you know, as you say, these kind of space telescopes will see these transits, that means watch the light of the star go down and then go back up because the planet moves in front of that star, but what we’d really like to do is confirm that, and that means figure out that orbit and then watch it happen again.

Jim Green: Kepler observed so many planets, and we were able with Kepler to determine the distribution of planets. Were there any surprises that came out of that?

Knicole Colon: So my goal in being an exoplanet scientist has been to understand how common planets are from our own solar system. So, how common are Jupiters? How common are Earths, right? But Kepler comes along and says, "Wait a minute. The most common size planet is actually smaller than Neptune in our own solar system." So, it's between the size of Earth and Neptune, and we have nothing like that in our solar system. So how is it that the most common-size planet is not found in our solar system? That blows my mind, and that means we have so much more to learn.

Jim Green: Yeah. Actually, that was the big surprise for me, too. You know, approaching it as a planetary scientist, I thought, "Okay, when nebulas collapse, we're going to get stars, but there are also going to be some big planets." I would have thought there would be a lot of Jupiters, but that isn't the case. These bigger planets that you call super Earths, or mini Neptunes, that are between the size of Earth and Neptune, really are these new planets that are so exciting to study.

Jim Green: Well, you mentioned this new type of planet. Is that what I would call your favorite type of planet that you're looking for, a super-Earth?

Knicole Colon: You know, it's one of them. I have a lot of favorites. That is certainly one, just because it is so different from our solar system, but there is kind of another emerging class that I'm pretty interested in, and these are what are called extremely low density planets, or I like to just call them puffy planets. Where they're so low density, imagine having the density of styrofoam, basically. And that's what we're talking about here.

Knicole Colon: And they're Jupiters in size, though, so it's kind of deceiving. You think, "Oh, they're just giant planets." But then they have really low masses, and I'm curious to know how did these guys forms and evolve, and retain this really fluffy atmosphere, because that's presumably what's happening here. So, finding that out-

Jim Green: That's right.

Knicole Colon: ... is interesting.

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Gravity Assist: Puffy Planets, Powerful Telescopes, with Knicole Colon (2)


NASA astrophysicists Knicole Colon and Elisa Quintana with stickers from some of NASA’s exoplanet missions. Credits: Knicole Colon

Jim Green: Indeed. Jupiter, if it was a big fish bowl, you could put a thousand Earths in that fish bowl, and yet Jupiter, its mass is only about 300 times the mass of the Earth. So, that means its density is much less than Earth's. So, there's something about what's in the core, what the composition of that is, whether there's rocky material there or not, and so there's a lot of physics yet in terms of planetary formation that these puffy, large planets will tell us about.

Knicole Colon: Absolutely.

Jim Green: Well, another activity that you're very much involved in is our new, fantastic telescope, the James Webb Space Telescope. What's your role in that particular mission?

Knicole Colon: Yeah. I'm very excited to have this role. It’s basically revolves around everything exoplanets, so I engage with the community on all things exoplanets, both in terms of doing public outreach, but also really communicating with scientists about how Webb can study exoplanets, and how it's already being planned to study exoplanets. So, we already have programs in the works to study exoplanets, so making sure they're aware of what's in the plan for its first year of science, for instance.

Knicole Colon: And really, I also work with the rest of the Webb team to make sure that we have all the necessary tools in place to analyze that exoplanet data once we get it, so that we can be sure to extract the scientific results and learn from them. You know,tThat's the end goal.

Knicole Colon: It's basically going to be able to access these long infrared wavelengths that we cannot currently access with space telescopes. And not only that, but it has improved sensitivity, so we can make really these measurements of really small signals. For instance, from atmospheres of exoplanets. But beyond you know, science and those types of observational capabilities, it's really neat to think about the technological aspects of Webb. I mean, Webb has this huge, 6.5 meter primary mirror, and it's actually made up of 18 separate segments that will unfold after the telescope launches and then they'll serve as a single mirror.

Knicole Colon: So, that whole unfolding in space thing is really fascinating, and making sure it works is a whole ‘nother game. And then not to mention Webb also has a sun shield that's literally the size of a tennis court, and that's going to help keep Webb cool, so that it can make these really sensitive measurements. So, all these different special kind of components come together to make sure we can do some really groundbreaking science.

Jim Green: Yeah, so Webb is the largest space telescope that we've ever put into orbit, and it should be absolutely fantastic in terms of its ability to see different objects in that infrared range. Anything that's in space that's hot will generate a signal it can see, and so all our planets are still cooling off from when they were made, 4.6 billion years ago. So, I'm too really excited about what Webb can do. Not only looking within our solar system, but well looking out at a variety of exoplanets. So, what do you think the biggest contribution Webb's going to be making in terms of looking at these exoplanets?

Knicole Colon: Webb is going to look at really a variety of planets, ranging from ones as small as Earth, that orbit stars much smaller than our own sun, to giant planets that orbit giant stars. So, I think Webb is really going to be able to give us new information beyond what Hubble has given us already. With Webb, we're going to be able to look for concrete evidence of methane, carbon monoxide, carbon dioxide, these types of chemicals in exoplanet atmospheres, and these are really important to understand how do these exoplanets form, how do their atmospheres form, how did they evolve? Because all of this, again, helps us with that journey to understand our own solar system planets. So, any information we can get is really going to help us move forward in our understanding of the universe, really.

Jim Green: So, indeed, if Webb sees these exoplanets and their atmospheres, what will it be looking for in the infrared?

Knicole Colon: Yeah, so there's actually two ways that Webb looks at exoplanets, and so we already talked about the one where Webb will look at transiting exoplanets. So, Webb will see a planet pass in front of, or sometimes it looks when the planet passes behind the star, and in that case, either way, you're measuring the dip in brightness from the system, and then you're extracting that information as a function of wavelength of light. And so, in the infrared, you end up looking for basically dips in the light that is telling you, "Oh, there's methane absorbing in the atmosphere of this planet." And that's something that we can see with Webb, and we can do this for all size exoplanets, from giant ones to small ones, so that's really exciting. And Webb will be able to do that for a lot of planets.

Knicole Colon: But then on the flip side, Webb also has the ability to take direct images of planets. So, it's basically like someone might take a picture with the camera on their phone. Of course, though, the instruments on Webb are designed differently, so that when you're taking a picture of a star with a planet, the instrument is designed so you suppress that starlight, because it's super bright compared to the planet, and you just want that faint little glow from the planet, and that's what we're trying to get at here. And from that, similarly, you can say, "Oh, is there methane, carbon dioxide, whatnot in the atmosphere?" From that little pale dot.

Knicole Colon: The difficulty, of course, is that the atmospheres of rocky planets are really, really thin, and so Webb will be able to provide... we'll say like a first glimpse into the atmospheres of rocky small planets that might be also the right temperature to have liquid water on their surface, and might be the right conditions to have life on their surface. But I think Webb is really the first step in a journey here, where we have future telescopes being designed right now and considered, that might be built, that could really push the boundaries even further and provide us with that really definitive evidence of, "Okay, this has an atmosphere conducive to life."

Jim Green: Well, that's really exciting. Do you personally think there's life beyond Earth?

Knicole Colon: You know, I do. I do think that. I have no idea what type of life there could be, if it's anything whatsoever like what's found on Earth, but at the same time, Earth has so many different types of life that exist in so many different environments, that I just don't see how there can't be life outside of Earth. Maybe we'll discover it in my lifetime. One can hope. But-

Jim Green: No. We've got to be able to do that. We're hot on the trail.

Knicole Colon: That's right.

Jim Green: So, don't give up. Get going and let's do that.

Jim Green: Well, Knicole, I always like to ask my guest to tell me what was that event or person, place, or thing that happened to them that got them so excited that they became the scientist they are today. I call that event a gravity assist. So, Knicole, what was your gravity assist?

Knicole Colon: Is it okay if I give two answers?

Jim Green: Of course. Yeah, sometimes we all need a little extra.

Knicole Colon: Yeah. Well, for me, it was kind of two simultaneous events. And really, it boils down to being a young teenager, and I fell in love with science fiction at the same time that my dad started encouraging me to have an interest in astronomy, and his interest came from the fact that he was just interested in everything, so he saw I started liking science fiction, and certain movies really inspired me, and he encouraged me to pursue astronomy. And those things really had me excited about the idea of being a scientist, and now to this day, I still am excited about being a scientist, so I guess it all worked out.

Jim Green: Well, I can see now, as you say the science fiction part of it, why you were so excited to find Tatooine, a planet orbiting two stars. But I had heard that you were really excited about the book that Carl Sagan wrote, Contact, and then the subsequent movie about finding life beyond Earth.

Knicole Colon: Yes. 100%. That is one of the first books and movies that just really floored me. I mean, I was wondering what would it really be like if we found life? How would humanity react? How would we communicate with them? Could I actually do something like this myself when I grow up? And here I am, however many years later.

Jim Green: That's right.

Knicole Colon: Working on that goal with TESS and Webb.

Jim Green: That's right. Indeed. Actually, you're right. We need to also start thinking ahead a little bit of what has to happen, or what will happen when we announce for sure that there is life beyond Earth, and how we're going to explain it, how we're going to interact with the public, what we think their interactions will be, their reactions, and try to anticipate those.

Knicole Colon: Yeah. It's going to be really interesting. That's why I hope I'm around when that happens, too. In my lifetime.

Jim Green: Well, just make it happen. I want you to do that. I want you to find it.

Knicole Colon: I'll work on that.

Jim Green: All right. Well, good. Great. Well, Knicole, thanks so much. I really enjoyed talking to you today about all your vast experience and the progress that we're making in looking for life beyond Earth with exoplanets.

Knicole Colon: Thank you so much for having me. I really enjoyed talking with you.

Jim Green: Well, join me next time as we continue our journey to look for life beyond Earth. I'm Jim Green, and this is your “Gravity Assist.”

Credits:
Lead producer: Elizabeth Landau
Audio engineer: Manny Cooper

Source: https://www.nasa.gov/mediacast/gravity-assist-puffy-planets-powerful-telescopes-with-knicole-colon

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Gravity Assist: Where are the Goldilocks Stars? With Giada Arney (1)
Jun 18, 2020


This illustration shows exoplanet Kepler-62f, a planet larger than Earth that orbits a K-type star. Credits: NASA Ames/JPL-Caltech/Tim Pyle

Without our Sun, there would be no life on Earth. The Sun gives us exactly the amount of heat we need to survive. But our Sun represents only one type of star in the universe. Smaller, fainter stars called K stars are more common in our galaxy and also have planets, but we know far less about them. Giada Arney, astrophysicist at NASA’s Goddard Space Flight Center, is looking at the potential for K stars to host habitable worlds. Learn about how stars affect planetary environments and why complex life on early Earth was impossible.

Jim Green: Well, life on Earth is the only life we know, and so that means that our star is so important to us, but there are other types of stars. What would life be like around different stars in those solar systems?

Giada Arney: Earth didn't have an ozone layer before and didn't use to have oxygen in its atmosphere, and these different kinds of alien Earths might be analogous to the kinds of alien exoplanets we might someday encounter.

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green: I'm here with Dr. Giada Arney and she is a research space scientist at NASA Goddard Space Flight Center. She has done research on astrobiology, exoplanets, organic hazes, Venus and planetary habitability. So today we're going to talk about how NASA looks for life beyond earth. Welcome Giada.

Giada Arney: Thanks Jim, I'm glad to be here.

Jim Green: Well, we now know there are more planets than stars in our Milky Way, and these stars come in all sizes and intensities. And I know you have a favorite star type that you look at. What do you think is the best type of star that could possibly have habitable planets?

Giada Arney: A lot of the time when people think about habitability in planets, we think just about the planet by itself. But it's really important to remember that planets orbit stars and planets and stars actually can interact with each other in really important ways that affect habitability. So I like to think about what I think of as Goldilocks stars. These are stars that I think might be just right to find life and habitable planets. These are called K stars or K dwarfs, to use astronomical jargon. So the Sun is G dwarf in astronomical jargon, you may have also heard of M dwarfs, or we also call those red dwarfs. Those are teeny, tiny stars. So K dwarfs are kind of in the middle between G dwarf Sun stars, and M dwarf tiny stars.

Jim Green: What's the difference between our Sun, a G-Star; and a K star, other than size?


Recording “Gravity Assist” at the NASA Goddard Space Flight Center. From left to right: NASA’s chief scientist Jim Green, "Gravity Assist" producer Elizabeth Landau, and astrophysicist Giada Arney. Credits: NASA/Katie Atkinson

Giada Arney: There's a historical convention where astronomers give stars these different designations with these different letters, they denote different things like their sizes and their luminosities. The scale for historical reasons goes O-B-A-F-G-K-M, from the biggest stars to the smallest stars. So K stars are smaller than the sun, they're less luminous than the sun, but they're bigger than the smallest kind of stars. They're also, I think, interestingly more numerous than the sun. There's more K dwarfs in our galaxy than there are sun-like stars.

Jim Green: Where do those classifications O and B and G and K come from?

Giada Arney: So back in the late 1800's, early 1900's at the Harvard Observatory, there were these women who are called computers and what their job was, to sift through these photographs of the sky and a lot of what they were doing was categorizing stars. And so one woman, Annie Jump Cannon, was the person who came up with the original stellar classification system.

Jim Green: Yeah. So her first class was A, and then she decided on B and C.

Giada Arney: Yeah, yeah. She gave them different letters, I think based on the strengths of different features that she was seeing in their spectra.

Jim Green: And then when she realized that it's really about a temperature, she had to reorder them but she kept that original classification.

Giada Arney: Yes, which we now use today. So it seems like, you might think, "Oh, where did these letters come from?" They actually came from a place where people were actually doing science.

Jim Green: How does the host star affect whether or not a planet around it may be habitable?

Giada Arney: The host star can affect habitability in a lot of different ways. For example, the lowest mass kind of stars, these M dwarfs that I mentioned, they're really active stars. They flare a lot, they produce a lot of high-energy radiation, constantly bombarding their poor little planets orbiting around them. And what makes it especially tough for the little planets is that because M dwarfs are so dim, you have to orbit really, really close to that campfire in order to stay warm. So you're orbiting super close and yet you're constantly getting bombarded by high-energy radiation, so that's not so good. But what I like about K dwarfs is that they're not nearly as active as M dwarfs.

Giada Arney: They're much less active, they produce a lot less high energy radiation, which is really good for habitability. And what makes them better than G dwarfs, potentially for looking for habitable planets, is that G dwarfs like our Sun are brighter than K dwarfs. So when you're looking for tiny little planets orbiting around them, it's harder to pull out those signals when you're looking around a really bright star, compared to when you're looking around a dimmer star.

Jim Green: So you know those M stars, those smaller ones, like TRAPPIST-1 is an M star. It had seven planets and three or four of them were in the habitable zone. But as you said, they were being hammered by the radiation from the star, the coronal mass ejections and everything else that happens. But that habitable zone is so close to the star, they're tidally locked just like our Moon is. So with K stars then, that habitable zone is further out.

Giada Arney: Right.

Jim Green: Do we expect those planets to be tidally locked?

Giada Arney: Not necessarily. The tricky thing about the habitable zone is we don't know whether the planets that are in the habitable zone are truly habitable yet. We actually have to make those observations. But I think right now, based on what we know, is that there is a lot of problems to be orbiting around an M dwarf, just because of the way their stars behave.

Giada Arney: There's a lot of things that M dwarfs do that can strip away habitability from a planet that K dwarfs do much less. But they still offer advantages for detectability because they're smaller than our Sun, so it's easier to see tiny planets orbiting around them.

Jim Green: So in your search for that K star with planets, how many are you looking at these days?

Giada Arney: Well, so I'm not actually an observer, I'm a modeler. So what I do is, I model systems in my computer and I try to understand what are the best kinds of stars for looking for planets with habitability in life. What we really need in order to actually observe planets around K dwarfs, is next-generation telescopes that we don't currently have, but hopefully will in the future.

Jim Green: So, when you do your modeling, what are you modeling exactly in these K stars? Different types of planets, different sizes, in and out of the habitable zone and the activity of the star itself?

Giada Arney: Yes. What I am mostly interested in modeling is, I'm trying to understand how the star impacts the planet's atmosphere. So I run what's called a photochemical climate model, where it helps me to understand how the atmosphere evolves in response to the star.

Jim Green: What do you mean by photochemistry?

Giada Arney: Well, ok, that’s a good question. Chemistry, right, is the interaction between different chemicals, different compounds. Photochemistry, so “photo” means light in this context. So this is chemistry that involves not just different chemical compounds but also light getting involved. So light can break apart different molecules and make new molecules. Light can split them apart, make these new molecules and those new molecules can react in different ways. And this is a really fundamental process that occurs in planetary atmospheres.

Giada Arney: So I can put a planet, make up an atmosphere on top of that planet, put it around a given star at whatever distance I want, make the planet whatever size I want, make the atmosphere whatever density I want, put that planet there and just see how it evolves in response to the star. One of the really interesting things I found that I was really excited about, is that bio signatures, these are remotely detectable signs of life, around K stars compared to G stars, it might be easier to detect them. At least a particular kind of bio signature, which is oxygen and methane together in the atmosphere is a really good sign of life.

Giada Arney: So when you see these two gases, oxygen and methane, in the planet's atmosphere together, that's really important because those gases are both produced by life and they destroy each other really rapidly.

Giada Arney: And the best way we can explain that is, life. That's how we have oxygen and methane in Earth's atmosphere. But because of the different amount of ultraviolet light the K dwarfs produce, you can end up getting a lot more methane in their atmospheres, even in the presence of oxygen. And that's really important because when you want to try to look for life elsewhere, you would love to try to detect these two gases together. And it might be quite hard to actually do that for a planet around a G dwarf, but much easier to do that for a planet around K dwarf.

Jim Green: So are we developing instruments that will enable us actually to look at a planet and its atmosphere?

Giada Arney: Yeah, we're developing those right now. One telescope that's going to fly soon is the James Webb Space Telescope. And that's going to make the first look at potentially habitable exoplanets. It will probably not be able to observe habitable planets or potentially habitable planets around K dwarfs. What it might be able to do is, it might be able to look for planets around M dwarfs. These are these much smaller stars. So when you have a much smaller star, it's much easier to observe the planet around it. To observe planets around brighter stars like K dwarfs so even G dwarfs, we're going to need even next generation telescopes beyond James Webb.

Jim Green: What kind of telescopes would we need next?

Giada Arney: Great question. James Webb for most of its exoplanet observations and for observations of planets like the TRAPPIST-1 planets, it's observing them with what's called the “transit technique,” where the planets pass directly in front of the star. From our point of view, it's kind of like a little tiny eclipse where we see these little dots passing in front of their stars. And so from those little tiny eclipses we can infer things about the planet, and also a little bit of the star, like it's blocked by the planet's atmosphere. And so we can learn things about what the planet's atmosphere is made of. And that's a really great technique for planets that orbit small stars and planets that have really small orbits, they transit frequently. And so that's typically the best kind of technique you'd use for planets or being low-mass stars like M dwarfs, where you're orbiting close to your star really quickly. So you get lots and lots and lots of transits.

Giada Arney: The size of the star is not too big compared to the size of the planet compared to bigger, brighter stars. To observe planets orbiting brighter stars like G dwarfs and K dwarfs, G dwarfs like our Sun and K dwarfs, you probably need to see the planets directly because it can be tricky to use the transit technique in that case. It's really hard to get enough signal to noise using the transit technique because the star's just so much bigger compared to the planet and because the star is brighter, it has to orbit farther away from the star in order to be in the habitable zone. And so your transits are much less frequent. Earth would only transit the Sun once a year if you were an alien observer, compared to an M dwarf where you can get transits every couple of days.

Giada Arney: So around those M dwarfs you get a lot more signal in the same amount of time. We want to be able to see the planets directly for these brighter stars. We need ways to block out the starlight and there's different technologies that we're developing right now in order to do that. One's called the starshade where you actually fly. It's this beautiful petal-shaped thing that fits in space and flies in front of the telescope. And you can position it between the telescope and the star and you can block out the starlight and see the planets orbiting. There's another thing called a coronagraph, which is like a starshade, but it sits inside the telescope. And both of these do things, something similar to like, if you’re try to see an airplane that's flying right next to the Sun and you use your hand to block out the Sun so you can see the airplane — that's what these technologies do. They're blocking out the really bright star to see the tiny planet that's nearby.

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Gravity Assist: Where are the Goldilocks Stars? With Giada Arney (2)


Astrophysicist Giada Arney in the Australian outback. Credits: Giada Arney

Jim Green: So when we do that, we block out the light and we look at the planet and the planet is illuminated. That means the light from the star reflects off the atmosphere and the atmosphere modifies that light and then we observe it.

Giada Arney: Right. What we're looking at, is direct reflected light with these kinds of next generation missions that would actually be able to block out the starlight. And again, it's really important to think about how stars modify their planetary atmospheres, because we don't just passively get warmed by the Sun. The Sun is actually modifying our atmosphere through these photochemical effects. And it's really important whenever we try to think about the kinds of biosignatures that we might see on exoplanets, to consider these photochemical effects, because we might get fooled if we don't think about that.

Jim Green: So this sounds complicated, where the star's light affects the photochemistry of the planet and the life on that planet is also affecting the photochemistry. And you have to tease that out.

Giada Arney: You have to think about all of these different things together, interacting with each other, and especially when you bring life into the equation, that makes it especially complicated. Life on Earth has modified our environment in really complicated ways. We think about something that's really important to habitability: The ozone layer, which on Earth blocks UV radiation from reaching the surface, so it's worse than getting a sunburn. If we didn't have an ozone and oxygen layer in our atmosphere, we would die from radiation poisoning really, really fast.

Jim Green: Well, you know, when you think about that, an element of that is, well that's our environment and we've evolved in that environment, but you know, maybe there's life that lives in a planet where the ozone is destroyed and the ultraviolet light comes in and they take that into account. Is that a possibility?

Giada Arney: Sure. Well, actually, there was life on Earth before the ozone layer existed. The ozone layer is on Earth because of life. Because eventually oxygenic photosynthesis evolved on our planet and it put oxygen in the atmosphere and that oxygen, because of photochemistry, this interaction between gases in our atmosphere and the starlight, that photochemistry transformed some of that oxygen in our atmosphere into ozone. And so these processes on other kinds of planets might play out in different ways. In some of my own simulations, I find that K dwarfs actually produce less ozone than a planet around a G-star, which might have implications for how much UV light reaches the surface on those stars. There's definitely tons of different scenarios that might be able to play out on different kinds of planets.

Jim Green: What are we doing here on Earth to help better predict where life might be found on other planets in our solar system?

Giada Arney: I use computer models to do this because I think it's really fun to let the universe be my sandbox where I can tune all these different knobs in my models and see what happens. So that's primarily what I do. We often forget that Earth itself is a planet, but Earth is a planet. And I think a lot about how we can think about Earth as an exoplanet to help us understand what we might look for and what we might see when we actually start looking for these pale blue, and other colored, dots around other stars.

Giada Arney: I also think a lot about different phases of Earth's history because when you think about Earth in the past, Earth is more than one planet and its environmental conditions were dramatically different in the past. I mentioned before that Earth didn't have an ozone layer before and didn't use to have oxygen in its atmosphere, and these different kinds of alien Earths might be analogous to the kinds of alien exoplanets we might someday encounter. So using modeling and using what we know from here I think is really useful.

Jim Green: So if Earth started out being so uninhabitable, and life was struggling to get through, how does that process work?

Giada Arney: Well, it would not have been habitable to us or a lot of the complex life that we have on Earth today, but it was habitable to the organisms that existed on early Earth. And that did arise in that context. What we consider habitable today, like oxygen is not a prerequisite for habitability. It is for us. We humans, we need oxygen to survive. But there's, even life that lives on Earth today that hates oxygen. And if you put them in an oxygenated environment, they would die. So on early Earth, there was no oxygen and that was okay. Life didn't want oxygen. In fact, when oxygen started to rise in our atmosphere, it poisoned a lot of life, we think. There was a huge calamity that may have occurred when oxygen levels first started to rise, because oxygen is really reactive and it's poisonous if you haven't evolved to deal with the reactivity of it.

Giada Arney: So the interactions between life and its environment, they're really complicated and there's really no, not necessarily any one size fits all, answer for what is a habitable environment. There's different habitable environments even on Earth for different kinds of life, and that's great because that broadens the kinds of environments we can look for on other kinds of planets when thinking about habitability.

Jim Green: So within our solar system, you've studied several planets, Venus in particular. What do you like about Venus and how do you look at that relative to other exoplanets?

Giada Arney: Well, what's great about Venus, is that it's so hard to understand what's under the clouds, just like it's so hard to understand what the exoplanet atmospheres are made out of at all right now. What I think is really compelling about Venus in particular is that I think Venus has a lot to tell us about how habitability can vary and evolve over time. Venus today is a really uninhabitable world. It's a planet where the surface temperature is hot enough to melt lead. And you might think, well, what does that planet have anything to tell us about habitability other than the fact that it doesn't have habitability, but there's evidence of Venus might've been habitable in the past.

Giada Arney: People think that it may have lost an ocean of liquid water that used to be on the surface and that was in response to the star. The Sun through normal stellar evolution processes, gets brighter over time and eventually got too hot on Venus for its oceans to be sustained. So again, this is an example of how stars and planets can interact to shape habitability. And Venus is a great example of the end-state of habitability. Earth might in the future look a lot more like Venus than it does the planet that we know and love today because the Sun is not stopping getting brighter over time. And this is a process that takes a really long time. It takes billions of years. But these are the kinds of time scales that we have to think about when we think about astronomy.

Jim Green: Yeah. So when we look like Venus, we better be on Mars.

Giada Arney: Yeah. Mars is going to be pretty nice then hopefully.

Jim Green: Do you think we're alone in the galaxy?

Giada Arney: Well, I think that life evolved on Earth as early as it could. When you look at Earth history, the geological record, life appeared almost as soon as Earth became habitable, at least as far as we can tell. And what that tells me is that, maybe it's not too hard for life to evolve if you have the right conditions and the right ingredients and the right kind of planet. So if habitable planets are common and I don't know how common they are, but I think there's probably some out there, then I think maybe at least some of those planets have life. So I would be surprised if we're alone in the galaxy.

Jim Green: Let me ask you this question then. Do you think we'll find evidence for life in the solar system beyond Earth first, or from an exoplanet?

Giada Arney: I love that question because it's such a cool way of thinking about planets holistically. A lot of the time we think about like exoplanets or solar system planets as separate planets, but I think it's exciting to think about them together as one population of planets. And I don't know, I'm really excited though about future solar system exploration of Europa. I know that the Europa Clipper is going to be visiting Europa and we're going to begin to understand what might exist under Europa's icy crust and in the ocean underneath, which might be habitable and might have life.

Giada Arney: And that's really exciting, and in the same timeframe we're going to begin to get the first observations of maybe potentially habitable exoplanets, and maybe if we're really lucky, discover biosignatures in their atmosphere. I think if we discovered life within or outside the solar system, in either case, if we make one positive discovery, that's going to tell us life is probably really common and our galaxy is teaming with inhabited worlds.

Jim Green: Well Giada, I always like to ask my guests to tell me, what was the event or person, place, or thing that got them so excited, that propelled them to become the scientist they are today. I call that a gravity assist. So what was your gravity assist?

Giada Arney: I used to really love going to the library as a kid and checking out books on science and especially the astronomy books. Those were my favorite of all time. And I think I checked out every single astronomy book from the library that was near my house when I was a little kid. But there was one book that I loved the most because on that book, it's called the Space Atlas. And there was this page in the Space Atlas, where the top of the page said, "Are we alone?" And it had this discussion of what I would now consider to be astrobiology. But at the time I didn't have that word for it and it had this picture of the Voyager Golden Record that was going out into the stars. And I just thought it was so amazing that we're sending this record out into the stars. Probably no aliens will ever find it, but just the idea that it could be found, was so amazing to me.

Jim Green: That's fantastic. Well, I really enjoyed talking to you about star, star types and how planets might actually be habitable or on other different types of stars. Thanks much.

Giada Arney: Thanks Jim. It's been great chatting.

Jim Green: Join me next time as we continue our journey to look for life beyond earth. I'm Jim Green and this is your Gravity Assist.

Credits:

Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper

Goddard audio support: Katie Atkinson

Source: https://www.nasa.gov/mediacast/gravity-assist-where-are-the-goldilocks-stars-with-giada-arney

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Gravity Assist: If They Call, Will We Listen? The Search for Technosignatures (1)
Jun 26, 2020


The Midwestern United States as seen from the International Space Station. Credits: NASA  (more on this photo:
https://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=ISS029&roll=E&frame=12564 )

So far we’ve talked about life in terms of its chemistry and telltale signs of biology. But what if there’s intelligent life out there in the universe that has created technologies just as good, or even more advanced, than our own? Some scientists are thinking about how we would detect the signals that would come from distant civilizations, if they are out there. Those signals are called “technosignatures.” Jason Wright, professor of astronomy and astrophysics at Penn State, has been thinking about the different technosignatures we could pick up using the telescopes we already have, and the telescopes that we could develop in the future.

Jim Green: If you lived on a planet around a distant star and you pointed a powerful telescope back to Earth, you might easily be able to pick up the signals from all of the technologies that we have developed. Could we find this type signals from another civilization on a distant planet somewhere in the galaxy? 

Jason Wright: We're already doing a lot of search for extra-terrestrial intelligence by building and developing and using all of these instruments. We just have to think of it that way.

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green:  I'm here with Dr. Jason Wright and he is a professor of astronomy and astrophysics at Penn State and a member of its Center for Exoplanets and Habitable Worlds. Welcome Jason, to “Gravity Assist.”

Jason Wright: Thank you very much, Jim. I'm really glad to be here.

Jim Green: Yeah. First, Jason, I want to congratulate you on being the recipient of the 2019 Drake Award. That's quite a distinction.

Jason Wright: Thank you very much. Yeah, I was really honored to get it. It's just amazing to get an award named after a pioneer like Frank Drake.

Jim Green:  Well, you're well known for discussing the important science that is really at the root of the Drake equation, so give us a little background on what that is.

Jason Wright:  Sure. The Drake equation was an equation that Frank Drake wrote down to try and estimate the number of communicating civilizations in the galaxy that we might be able to detect with radio telescopes. And so he wanted to quantify and formalize the general sense we have that there are so many hundreds of billions of stars in the galaxy, surely at least one of them has some kind of technological species that might be communicating with us. So we started with the number of stars in the galaxy, and then attempted to estimate what fraction of those have planets, what fraction of those planets might host life, what fraction of those planets with life might have complex life that could build tools, and then what fraction of that life is communicating with us right now. And so it allows us to kind of break down the whole problem of finding other life in the galaxy into individual pieces that we can study and attempt to estimate numbers for.

Jason Wright: We now know that something like one in 10 or one in four of those hundreds of billions of stars in the galaxy really do have planets, rocky planets that could have liquid water on the surface of them. Now we haven't discovered any planets with liquid water on them other than the Earth, but we've found many that may have liquid water. And so just that by itself means that there are hundreds of billions of potential sites for life in the galaxy and he didn't know that.

Jason Wright: He didn't know if most or even any other stars had planets around them when he first wrote down the equation. So that has helped a lot. But the other terms in the equation are still pretty fuzzy. We only have one example of life arising on any planet, our own, but if we were to find, say, microbes on Mars or signs of metabolism in the plumes coming out of Enceladus, that would suggest that wherever you have water, you'll have life arise and that would greatly increase the chances that there's someone out there trying to get ahold of us.

Jim Green: Well, the Drake Award is given to scientists by the Search for Extra-Terrestrial Intelligence Institute. This is the SETI Institute. So please tell us how SETI is looking for extra-terrestrial intelligence.

Jason Wright: Right, so the term SETI, S-E-T-I, is the Search for Extra-Terrestrial Intelligence and it actually began at NASA as a radio program to try and detect the sorts of signals that Frank Drake pioneered. But at some point, Congress directed NASA to stop doing that. And so the SETI Institute in California was founded as a way for philanthropic funds to support the search when NASA wouldn't do or couldn't do it because Congress told them. And so the SETI Institute now, for decades, has been the hub for the search for radio signals from other stars and through the philanthropic contributions of people like Barney Oliver and Paul Allen, they've managed to really advance the field and carry it forward and today radio SETI is really mature and scanning the skies all the time for signs of alien life.

Jim Green: So these are potential radio transmissions that SETI might observe coming from sources elsewhere in the galaxy. We call those signatures of technology, or technosignature. What else is a technosignature?

Jason Wright: Jill Tarter, who's one of the founders of this field and for a long time led the SETI Institute, wanted to sort of reframe the whole search for technology in the galaxy and point out that it's not just looking for really powerful ham radio signals from another star. It's really the search for any kind of technology that we might be able to detect. And so she looked at how NASA had developed the idea of biosignatures, the ways that we could tell that life was somewhere else, such as microbes on Mars or certain chemicals in the atmosphere of an exoplanet and said, "Well, what we're doing is looking for techno signatures and they might not be radio waves. They could be laser pulses. We might detect the extra heat on a planet coming from all of its power plants and cities. We might detect very large structures and orbit around other stars as they pass between the stars and the Earth. There are lots of things we can imagine doing to try and find signals or signs of technology other than just narrow band radio transmit."

Jim Green: Well, these narrow band radio transmissions are some of the things that we do here on this planet. So could another civilization pickup our technosignatures, or our radio signatures?

Jason Wright: I think so. So if we were looking at the sun from afar, say that Earth were actually around Alpha Centauri, looking back at the Sun, would we be able to tell that the sun had the Earth on it and that Earth had liquid water and that Earth had life and that Earth had humans? And even just knowing that the sun had a planet like Earth around it would be very challenging with the technology we have today. At that distance it's very hard to detect, but it's possible. Knowing that it had an atmosphere, knowing it had liquid water, that is really at the moment beyond our capabilities, but NASA is working on new space telescopes that could figure something like that out. But to know that Earth had life is extremely challenging. It just doesn't put a big imprint on the Earth that's detectable from another star.

Jason Wright: However, if they knew what frequencies to check and when to check and what they were looking for, they would be able to detect, for instance, our interplanetary radar, that we use to find the distance to Venus and study the rotations of asteroids. They might even be able to detect our ICBM radars that are constantly scanning to make sure that missiles aren't flying around the world. They might be able to detect, perhaps eventually, our interplanetary probes that have escaped the solar system and are now flying and interstellar space. And so it's very possible that our technosignatures are the most obvious signs that there is any life in the solar system. So it stands to reason if we're looking at other stars, those technosignatures might be more obvious than the biosignatures. So if we want to find life in the universe, it might be most fruitful to look for technosignatures instead of biosignatures because after all, that's probably true for us.

Jim Green: What are some of the kinds of tools that we either have today, or we need to develop to really go after technosignatures?

Jason Wright: It's interesting because astronomers like to build these general kinds of telescopes that are looking for all kinds of things out there. And so when we think about how are we going to go to technology, the dream instruments that we would build to do that are the same ones that we're already building to do all sorts of other kinds of astronomy and astrophysics and planetary science. So the sorts of things we would build our larger rays of radio telescopes, and sure enough, those already exist. And in fact, a lot of the work done at the SETI Institute and at the UC Berkeley SETI Research Center and other places that do SETI, piggyback on those telescopes and while they're being used for other science, they also look for radio signals.

Jason Wright: Similarly, there's all sorts of NASA assets. We've got the WISE satellite that surveyed the entire sky and infrared wavelengths. We have coming up the James Webb Space Telescope that's going to be able to take just absolutely amazing data from all sorts of stars in the universe. These are the sorts of things that we would hope would be built to go looking for technosignatures. So I would say we're already doing a lot of search for extra-terrestrial intelligence by building and developing and using all of these instruments. We just have to think of it that way and task those telescopes to do SETI work in addition to the other work that they are doing.

Jim Green: And when you think about a planet, perhaps an Earth-like planet orbiting it's sun, we could see it perhaps away from the sun's intense light during the time when the sun's light is shining on it in the day, but also as the planet goes around the sun at its nighttime. And if there's life on those kinds of planets, what kind of things do you think we can see in the atmospheres of those exoplanets?

Jason Wright: Yeah, that's exactly right. These planets are very small and so there's two ways that you can go after trying to find biosignatures or technosignatures on them. One of them, as you say, is that with these very large fancy telescopes, many of which NASA is putting into space, we can separate the light from the planet and actually take an image of the planet as maybe a pale blue dot and then study it spectrally. And then the other way is when it passes in front of the star, the star light will filter through the atmosphere and the chemicals in the atmosphere will block certain colors of light and certain patterns of chemicals in the atmosphere would be indicative of life.

Jason Wright: So for instance, if the Earth passed between the sun and another star, and you were trying to study the Earth's atmosphere, that way you would notice that the Earth's atmosphere contains both methane and oxygen at the same time and that's very unusual because lightning should make the oxygen and methane combined into carbon dioxide and water and make at least one of them disappear. The reason we have all that methane is because of things like cows and metabolism of mammals just creates lots of methane and so that's a sign of life. Also, however, if you made very sensitive measurements, you might detect that the atmosphere contains chlorofluorocarbons or CFCs. Now we don't put much of those in the atmosphere anymore because we now understand how bad it is for the ozone layer, but that's absolutely artificial. Nature does not make CFC and so that's how you could tell the technosignature in our atmosphere.

Jim Green: Yeah, so in other words, the technology of that planet is actually generating those trace gases, which are affecting the atmosphere and if we can tease that out of the spectrum, we got it, then we'll know that there's advanced life on those planets.

Jason Wright: And it's even better than that because scientists can dream up scenarios without any life where you might get methane and oxygen at the same time. It shouldn't be common, but it could happen. There's really no way that nature produces CFCs. That means you have to have technology. And so if you see that, you know you've got life. So in a lot of ways, searching for technosignatures is a stronger way to go because when you find it, you've really found it.

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Gravity Assist: If They Call, Will We Listen? The Search for Technosignatures (2)


Jason Wright is a professor of astronomy and astrophysics at Penn State. Credits: Jody Barshinger

Jim Green: Now you were involved in a survey going back a few years called Glimpsing Heat from Alien Technologies. What was that about and what did you learn?

Jason Wright: So there are actually a lot of ways, as we said, to go looking for technosignatures and most of them actually all go back to about 1960 to 1964. There's looking for radio waves, there's looking for laser light, there's looking for probes that might be in the solar system right now, but one of them hypothesized by Freeman Dyson, who sadly died just a couple of months ago,

Jim Green: Yes, indeed.

Jason Wright: …was that we could look for large technologies that orbit around the star. So Freeman Dyson's idea was that we don't know what alien technology is going to be like, but we can be pretty sure it will use energy. That's almost the definition of technology. And so where is it going to get all of that energy and how much could it possibly use? If you give humans a billion years to develop technology, how much energy will we need to power it?

Jason Wright: And his answer was that the most energy that they could possibly use was all the energy coming from their star. And so if they are going to capture all, or even just 1% of the energy coming from the star, well, it would use that energy and then it would have to give it up as heat. So for instance, my computer right now is warm and the reason it's warm is it's getting energy from electricity, it's going to use that energy to help me do this interview and then when it's done with the energy, it doesn't disappear. The energy has to come off as heat. So if there's technology around a star using even just 1% of the star light, then not 1% of star light should be coming off as heat and we can detect that heat at infrared wavelengths. So the idea behind GHAT, Glimpsing Heat from Alien Technologies, was that NASA had just finished an all-sky survey to look at how much heat was coming off of every star and galaxy in the universe.

Jason Wright: And so I thought, well, that's great. That's exactly what Freeman Dyson had hoped someone would do, but no one could really do very well before that satellite flew. So it wasn't at the time something NASA would have been interested in looking at with its telescope, but we did get some funds from the Templeton Foundation and so we were able to hire a researcher to go through the WISE database and try and put limits on what's the most heat coming off of every star and every galaxy, maybe galaxies are filled with technology. And so we put some of the first strong upper limits on how much heat is coming out of all of the technology of other galaxies, which was just a pilot study. We weren't able to put any really firm upper limits on it, but we could say things for instance, like, "There aren't any galaxies where every single star has a hundred percent of its light being used up by technology," which we actually didn't know before. It's not a surprise, but it's a first step and I'm hoping we can do a lot better in the future.

Jim Green: Well, let me ask you this, let's say you discovered evidence for a technosignature and even better, that it was confirmed. You have to put yourself in that future thinking, what would you do next?

Jason Wright: Yeah. So the confirm part is really important. I'm glad you brought that up. If you're looking with a radio telescope and you see that signal, you're basically done, unless that signal came from Earth, and you do have to rule that out, but you can roll that out pretty quickly. Unless it came from Earth, that signal has to be a technology from another planet when you find it. So then you're done. But if you go looking for things like the heat of technology, or you go looking for large technosignatures or mega structures passing in front of stars, or what you think is chlorofluorocarbons in the atmosphere of another planet, you're not going to be absolutely sure what you have. What you're going to have is some sort of anomaly. And so you're going to have to follow that anomaly up and it's going to take a long time.

Jason Wright: And so I think it'll be a lot like, "Well, we have an interesting candidate. Wow, that candidate is stronger than we thought, Oh, that thing we thought it might've been isn't and it really could be aliens." And it'll just be a slow process where more and more astronomers are convinced, yes, that really is aliens. Now, if it's confirmed, if we get that radio signal or that laser signal from that source, and there it is, we know what it is, then the S in SETI just changes because it's the Search for Extra-Terrestrial Intelligence, well it will become the Study of Extra-Terrestrial Intelligence. And at that point, it's going to depend on what it is that we have found and we'll have to figure out how to study it.

Jim Green: Yeah, you're right. Probably every telescope in the world will be looking at it.

Jason Wright: It'll be a big deal.

Jim Green: It'll be a big deal. And then, okay, let's say you want to be able to communicate with it, I would think. So in other words, if a technosignature came from a star, a thousand light-years away, that means it's already been a thousand years since that was emitted for us to see it. How would we know that that civilization is still around?

Jason Wright: Oh, well, yeah, the ping time, that's going to be a problem. So if it's a thousand light years away, which is a very reasonable distance, then if we have a message that looks like it's inviting a response and if we should choose to respond, and I don't even want to go there, then we'll send that back and it'll take a thousand years before they get it. And so that's 2,000 years from their perspective of sending it out and it coming back and 2,000 years ago, well, we had very different technology levels and very different social structures and completely different governments and societies. And so you can imagine that, yeah, it'll be a very different place when our message finally gets back, if they're even there at all.

Jim Green: Well, you've been working on this topic now for many, many years. What really inspires you to keep going on it?

Jason Wright: I really like puzzles that no one else seems to be working on and this is not a field with a lot of people working in it. I also really liked that it's a big question that captures everybody's attention. A lot of times we find our vocations working on important problems, but then when our Aunt Millie at Christmas asks what we work on, we have to figure out how to explain it and why it's relevant and her eyes glaze over and it can be hard. But when I say I'm looking for signs of technological life in the galaxy to see if we're alone, nobody's eyes glaze over. They get wider. Everyone understands how neat that is. So it's a great problem to work on where there's a lot of headway to be made and everybody gets why it's so important. It's a lot of fun.

Jim Green: Good, that's interesting. Well, Jason, I always like to ask my guests to tell me what was the event in their life, whether it's a person place or thing, something that got them so excited about becoming the scientist they are today. I call that event a Gravity Assist. So Jason, what was your Gravity Assist?

Jason Wright: Oh man. It's funny, I've wanted to be an astronomer for as long as I can remember so my Gravity Assist might've come out of is pretty young. One thing that's always struck me about my career arc is that when I was six, I wanted to be an astronomer, but I had no idea what that meant. I didn't know if I was any good at it, I didn't know what being an astronomer was day to day and so at every stage of my career, when I got to Boston University and first got to do some research and take my physics classes and then at UC Berkeley, where I started doing much more research and much more difficult classes and then when I started as a professor here, I started advising students, I started teaching courses, at every step along the way, I discovered that I really enjoyed what I was doing and that I was really good at it.

Jason Wright: And so I've been incredibly lucky. And so maybe it's more like Voyager leaving the solar system. There wasn't just one gravity assist. Every time it went by one of the giant planets, it went a little bit faster and it headed on to its next destination and every gravity assist was just right. And if any one of those have been unlucky and missed, not that NASA would have missed, but it was a difficult calculation, it wouldn't have made it, but it did. And so I think my career trajectory maybe is more like Voyager’s.

Jim Green: Well, I understand completely and you've got to have those little nudges along the way to keep you going sometimes. And, you know, we've gotten to the point where we find so many things out there that I would call circumstantial evidence that there's life beyond Earth, but there's so many of them. It's almost inconceivable to me to think that there's no life beyond Earth and I think you're in that same, same bucket that I am in that respect.

Jim Green: Early on, Frank Drake worked with Carl Sagan. They went to the Arecibo telescope and they fired off a message and that means they were trying to send a technosignature. Should we go back to that process?

Jason Wright: It's a neat question. The Arecibo Message, as it's called, was a fantastic project. It has inspired so many people to think about this problem, just like the Drake equation did. I mean an introductory astronomy textbook is almost guaranteed to have the Arecibo message in it for students to try and decipher and understand. But in that way, I think the Arecibo message was really for us. They didn't have any expectation that they'd get a response, certainly not in their lifetimes, because they sent it to stars, as you say, that are thousands of light years away. And it was just one very brief message.

Jason Wright: And so they'd have to be listening to the Earth at just the right moment when that very weak signal arrived for them to know anything about us. So I do think that things like that, the Voyager records that Carl Sagan helped put together that are right now headed off into interstellar space, the plaques on the Pioneer probes headed into interstellar space with messages inscribed on them. I think it inspires humans to think about this problem, to think about what it would be like to actually contact other life. As far as whether we should do it because we're trying to get a response, I think it's very unlikely that we can do anything more obvious than we're already doing with our radar and the pollution and the atmosphere and all of our other activities. I think all of that is much more obvious than any of these feeble little messages.

Jim Green: Yeah, actually I liked very much the way you said that and that is: those messages are for us.

Jim Green: So Jason, thanks so much for a really stimulating discussion on technosignatures and what they are.

Jason Wright: My pleasure, thanks for having me.

Jim Green: Well, join me next time as we continue our journey to look for life beyond Earth. I'm Jim Green and this is your “Gravity Assist.”

Credits:

Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper

Source: https://www.nasa.gov/mediacast/gravity-assist-if-they-call-will-we-listen-the-search-for-technosignatures/

[Orionid]

Gravity Assist: She Protects Other Planets from Our Germs (1)
Jul 17, 2020


Planetary protection specialists with the cruise stage of the Mars 2020 Perseverance rover on March 20, 2018. From left to right: Kristina Stott, Planetary Protection Engineer for the Mars 2020 mission; Moogega Stricker, Mars 2020 Planetary Protection Lead Engineer; Lisa Pratt, NASA Planetary Protection Officer; and Brian Shirey, Mars 2020 Deputy Lead Planetary Protection Engineer.  Credits: Courtesy of Moogega Stricker

As we explore Mars and other places in the solar system that might have life, scientists who work in Planetary Protection are busy making sure that we don’t contaminate them. While engineers prepare the Perseverance Rover for launch, Lisa Pratt, NASA’s Planetary Protection Officer, is making sure that it’s not carrying too many spores — cells that could re-activate and transport Earthly bacteria to Mars. It’s especially important to keep Perseverance clean because it will collect samples on Mars that will one day return to Earth. Learn what your hand sanitizer has in common with NASA’s clean rooms, and how scientists are thinking about protecting Mars in terms of future human missions.



Jim Green: If we return a sample from Mars, can we identify life in that sample?

Lisa Pratt: Can we go there and sustain ourselves without harming Mars if there is something on Mars that could be harmed?

Jim Green: Hi, I'm Jim Green, chief scientist at NASA, and this is Gravity Assist.

Jim Green: I'm here with Dr. Lisa Pratt, and she's NASA's Planetary Protection Officer. Welcome, Lisa, to Gravity Assist.

Lisa Pratt: Hey. Thank you, Jim.

Jim Green: Well, you've had a distinguished career in biogeochemistry and astrobiology, and the Planetary Protection Officer name, that sounds really cool. In fact, I've received letters from kids all over the world, and one of them called your position, the Guardian of the Galaxy. I can't help but think that every time I talk to you. But let's start with the basics. What is planetary protection?

Lisa Pratt: Jim, I wish I could tell you that I was, in fact, the Guardian of the Galaxy, but the reality is a little more mundane. Planetary protection is focused on limiting biological contamination of other worlds with terrestrial organisms, that's organisms from earth, and preventing the return of harmful potential extraterrestrial organisms or just organic materials when samples are returned Earth during robotic sample return or in the future when astronauts come back to Earth from exploration missions to other worlds.

Jim Green: We send things all over the place, and the next big mission is, of course, Perseverance, and it's going to Mars. So when NASA wants to send a new rover to Mars, what do you do?

Lisa Pratt: Well, Jim, right from the very earliest phase of mission design, when that light bulb first comes on with an idea for a new mission, the Office of Planetary Protection provides advice and guidance to the engineering team on heat sterilization, or alternative chemical cleaning methods, such as vapor hydrogen peroxide. Some spacecraft materials can be cleaned and others cannot, and we want to be sure that we're designing a spacecraft that will tolerate the cleaning procedures necessary to go to the three places we care about right now, most deeply in terms of contamination and that's Mars, Enceladus, and Europa.

Lisa Pratt: When we have a mission that's being assembled for one of those locations, then there's actually an independent auditor from our office that travels to all the facilities where parts like solar panels or parachutes are being manufactured, and we take samples to determine the level of biological cleanliness.

Lisa Pratt: Every day, I actually review data on the number of spores being sampled and detected on Perseverance as we get ready for launch.

Jim Green: So Lisa, what is a spore exactly? Is it biologically made up of many different things?

Lisa Pratt: Jim, a spore is a tiny microscopic resting cell that only certain types of bacteria can make, and they make spores, a process called sporulation, when the environmental conditions get challenging and it looks like they're going to have to shut down, they're not going to continue to be active. But in the process of making that spore, that single-cell entity, they wrap it in layers of highly resistant biopolymers. They seal it off and thereby they create the possibility of that spore later breaking open and turning back into a viable organism that can replicate and grow. The reason going ... and this goes back to Viking. It's really the Viking planetary protection biologists that thought this through and said, "Of all of the entities known on Earth that are biological, the only thing we think that could get on a spacecraft, not be seen in an inspection and stay viable would be a hardy spore."

Lisa Pratt: So we don't even monitor all of the spores, which you would be monitoring if you were making medical devices like implants and things like that. For us, we actually take a wipe of a spacecraft surface, or we take a tiny little swab that looks like a slightly large Q-tip, and then we heat shock that sample to kill the wimpy organisms, because we only want to know how much contamination is there that could survive the journey, launch, travel, cruise stage and the landing and the exposure to another planet. Those are the NASA Standard Assay, the NSA, spores.

Lisa Pratt: There are international guidelines for spore cleanliness. The total requirement for all spacecraft elements impacting Mars is 500,000 spores including the rover, aeroshell, descent stage, and parachute That sounds like a lot, but the requirement is less than 300 spores per square meter of exposed rover surface. Spores are tiny, barely visible with a light microscope, so 300 spores per square meter can be imagined as just 28 tennis balls on an entire football field.

Lisa Pratt: That's thousands of times less than our spacecraft would carry if we didn't build them in a clean room facility, if we didn't constantly wipe them with a cleaning fluid specific to biological cleanliness, like 70% isopropyl alcohol, which is what we all now read the labels on our hand sanitizer under the current pandemic to make sure that we're using at least 70%, just what we use on spacecraft.

Jim Green: Well, what's riding with Percy, and I like that nickname, Percy.

Lisa Pratt: Oh I do too.

Jim Green: So but what's riding with Percy is the Ingenuity helicopter. This is really a fabulous idea to what we call a technology demonstration, and we hope it works. But does that also have some sort of planetary protection requirements on it?

Lisa Pratt: Yes, it does. It's been held to about the same standards as that upper deck of the rover, but not nearly as rigorous as the sterilization for the sample tubes and drill, or the wheels. That's because it's a very different kind of activity. It will not, in any way, be associated with the return of samples to Earth. So part of what we're doing with the tubes and the drill is we're not just worrying about what we take to Mars, that's forward contamination. We're very concerned about what might come back in those samples, that's backward planetary protection. Backward planetary protection ensures that we do not bring something harmful and release it into the terrestrial environment.

Jim Green: Well, I think I have one of these samples and a sample tube right here with me. So when I was out at JPL not too long ago, and I went into the lab where they were testing the core, I was able to walk out with one of the cores. So they had just-

Lisa Pratt: Oh, look at that.

Jim Green: Yeah, yeah. They just took this circular tube that has a cutting mechanism, and it cuts into the rock and then creates this core. Then they break it off, and then that is put into a sample tube and that's what the sample tube looks like. As you say, these have to be cleaned really well…

Jim Green: You know, there are places on Mars I would dearly love to be able to really interrogate, and one of those places is what we believe ... We call them reoccurring slope lineae. This is these long lines of dark material that appear every summer. We now know that many of them, maybe not all, but many of them actually could be briny water. What would it take for a rover in planetary protection example to be able to go over and look at that, potential water streak coming out of a crater?

Lisa Pratt: Jim, that's a really good question, and one that I think the Perseverance rover drilling caching assembly prepares us to do because we have been successful in sterilizing at a high temperature for many, many hours in a way that would meet the requirement for going into a place where we might encounter a liquid water environment. So I actually think that what we're learning from this mission, to prepare for sample return, is going to put us in a good place to actually design a mission where we're going to reach towards and in some way sample one of these recurring slope lineae, which I usually just call RSLs because if I don't, it's a tongue twister.

Lisa Pratt: I also think that what we're learning with the rock drilling system on Perseverance is how we might clean a drilling system that would melt drill into ground ice or rotary drill into an ice cap.

Jim Green: Curiosity landed in August of 2012, and so it's been there many years in that environment. Do we expect many spores to have survived on its surfaces?

Lisa Pratt: Jim, even if the physical entity is there, because again, it's made out of very resilient biopolymers, it's extremely unlikely that that spore is viable, and that's what matters here. What matters is that an organism can come back to life, grow and replicate and spread. My feeling is, and I love it if we had the opportunity to think this through, my guess is that the Curiosity rover is now clean enough that if it were to encounter an RSL or something interesting to explore, that it would be clean enough that we as an international community, because we would probably discuss this through COSPAR, the committee on space exploration for which you are NASA's representative to the planetary protection panel.

Jim Green: True.

Lisa Pratt: I think we would conclude that that spacecraft is now as clean or even cleaner than what we could ever accomplish on Earth and get it to the launch pad and get it on its way.

Jim Green: Yeah. For all the research that we have done, that really makes sense to me too.

[Orionid]

Gravity Assist: She Protects Other Planets from Our Germs (2)
Jul 17, 2020


NASA Planetary Protection Officer Lisa Pratt with the R25 engine at Marshall Space Flight Center.
Credits: Courtesy of Lisa Pratt

Jim Green: Well, big discussions are going on at NASA on how we're going to send humans to Mars. What do we have to do to protect Mars and protect the humans that are there?

Lisa Pratt: We need to get a lot smarter than we are right now, and that's what we're going to do with the Moon. The Artemis campaign, the Gateway orbiting facility and the sorties or extended missions down to the surface of the Moon. That's the proving ground for Mars, Jim. If we can study how the microbes from humans leak out of the cuffs of our space suit or get out of the air handling systems in our habitats or trail along behind us on the wheels of our vehicles, then we'll learn how to prevent that or we'll develop technologies for sterilization of material when we're at Mars. Then we'll be able to do that exploration without causing harmful contamination of Mars. I say that because we don't know right now. We don't have the data we need to understand whether or not there's indigenous Martian life. We're pretty sure there's nothing at the surface because we've been looking.

Lisa Pratt: We've been looking from orbit, we've been looking from rovers, we've been looking from platforms. We don't see anything with the characteristics of life as we know it on Earth. But subsurface, if it was ever there and it evolved and adapted, and I think it's quite possible it retreated into the subsurface where we believe there is to the present day liquid water below the ice table. We certainly do not want to do something that would contaminate or compete with a potential Martian life form before we've had a chance to study it and understand it. It would be our first contact, and that's-

Jim Green: Yeah, right.

Lisa Pratt: ...a one-time only, don't mess it up kind of event and exploration.

Jim Green: It would be. It would be. Well, I'm going to I guess speculate, but I'm going to think about a potential future, and that is, let's say we find life on Mars. Is it possible that we could ... And it's below the surface, it's subsurface, maybe living in the aquifers where there's water and there's a lot of possibilities for that because we have an enormous amount of life below our feet too on this planet. Do you think we could get to the point where humans and these Martians could coexist, and what would that look like?

Lisa Pratt: Well, Jim, like you I'm sort of a hopeless optimist about what scientists and engineers are capable of doing, and I think it is possible. But I think we need to understand it and be aware of how we would bio barrier or very carefully control our waste and our agriculture. Because if we're going to be up there for extended periods of time, we need to be able to grow our own food, and that's a very different microbiome from just the human body, which we know has a signature.

Lisa Pratt: But when we start growing food, now we've got individual organisms that live in and on the roots of plants, mycorrhizal fungi that have a distinct characteristic, and bacteria as well. So we need to be very, very careful initially so we don't do something inadvertent and irreversible. Then I think there is a possibility in the future that we can be there and we can study. Frankly, we're going to have to learn if there is something in the subsurface, how to not have it get inside our habitats, and in some way present harmful contamination to us. It's very complicated.

Lisa Pratt: Very complicated relationship—

Jim Green: It is.

Lisa Pratt: ... that we'll have to develop. But again, in the same way, the Moon is the proving ground for Mars. I think Mars is the proving ground for the extraordinary icy worlds that are out there around Saturn and Jupiter. Let's make sure we know what we're doing in a very dry, hostile, cold terrestrial planet before we go to an icy moon.

Jim Green: I'm going to guess that you believe there's life beyond Earth.

Lisa Pratt: Jim, I would be absolutely flabbergasted if there was not life elsewhere in our solar system, because I think evolutionary biology has really changed over just the past two decades. Once we began to realize that there is essentially no place on Earth that doesn't have living organisms, it makes it very hard for me to think that life only got started here. The very fact that we don't know what the origin of life is on earth, we don't have a geologic record that gets us back in time far enough with unaltered materials to know what the origin looked like on earth, also makes me wonder if the origin was someplace else and something arrived on Earth ready to go or partially formed, or…and any of those ideas makes me keep my mind open about life elsewhere in our solar system.

Lisa Pratt: If it's there any place else in our solar system, then I think we will have to conclude that on the spectrum from rare to common, that it's going to be common. If we don't find any vestige of a life form, any place else in our solar system, that's going to push us towards rare.

Jim Green: Well, when you look out into the solar system, where do you think we will find it first?

Lisa Pratt: I'm still cautiously optimistic about Mars because of the methane mystery. We see these pulses of elevated methane in the atmosphere. Not only do we have no explanation for where that methane comes from, we don't have an explanation for how that methane is removed from the atmosphere. We have a great mystery on Mars right now, and that's why as the Planetary Protection Officer—

Jim Green: Yes, we do

Lisa Pratt: I want to see us continue to explore with a very, very careful eye on forward contamination.

Lisa Pratt: That gets back to your question about, can we go there and sustain ourselves without harming Mars if there is something on Mars that could be harmed? Ultimately, I think it's a better bet to look in the oceans beneath the ice covers in places like Europa and Enceladus.

Jim Green: Let's say we brought the samples back from Percy, and now we've started to interrogate them. Do you think we know enough to be able to say these samples, we can delineate things that we brought that actually have come back from those things that are indigenous to Mars?

Lisa Pratt: Jim, that would be a false positive. It would mean could we or do we need to worry about being confused and misidentifying something that made a round trip with something that came from Mars itself? I frankly, and we've spent a lot of time discussing this with outside experts, I have very little worry about a false positive. And the reason for that is that we are archiving samples from the spacecraft, from the facility, from the launch pad, and we are storing and saving those samples for future study so that we know a great deal about everything that could have potentially gotten on that spacecraft and flown with us.

Jim Green: Wow, that sounds great. Well, Lisa, I always like to ask my guests to tell me what was that event or person, place or thing that happened to him that got him so excited about being the scientist they are today, and I call that a gravity assist. Lisa, what was your gravity assist?

Lisa Pratt: Jim, it's hard for me to point to a single event because I think you're aware that I had quite a number of not false starts, but moved down one path with my education and then said, "This really doesn't interest me that much." I went off to college as a Spanish major.

Jim Green: Wow.

Lisa Pratt: Even though I had taken a lot of math and science in high school and knew that that was something I was good at, I didn't see any role models, I didn't see any way that that was going to—

Jim Green: Wow.

Lisa Pratt: ... work out. Then I realized that I really still fundamentally loved biology in particular. So I started taking biology classes, and then I decided I didn't want to be killing frogs in biology labs. This was at a time when we were still working with live animals in undergraduate labs.

Lisa Pratt: I had an inspirational moment when I decided I'm a botanist. Plants don't bleed. So I actually transferred to the University of North Carolina as a botany major. Then if there was a pivotal gravity assist for me, it was in my senior year when I took my first geology course. The instructor, John Dennison at Chapel Hill, had a way of talking about time travel through study of the geologic record, through stratigraphy that was so all inspiring that I knew that I was even more passionate and more interested in the history of life on Earth and the evolution of life on Earth through the study of the ancient rock record. I was more interested in that than living plants.

Lisa Pratt: I guess that's my gravity assist. It's what serendipitously gave me dual degrees in life sciences and Earth sciences that actually positioned me ultimately to be competitive for the Planetary Protection Officer position when it was advertised and opened three years ago.

Jim Green: I was just so delighted that you applied. What made you decide to do that?

Lisa Pratt: This is a strange and wonderful story about role reversal. A number of people, both inside and outside NASA, had let me know that the position was open and I kept saying, "No. Maybe 10 years ago, it's too late in my career," and I made the mistake. Well, maybe it was a mistake, maybe it's the best thing that could have happened. I was talking to my daughter about it. She's an engineering graduate student at Stanford, and I said, "This position is open," and that began weeks of relentless work on her part to-

Jim Green: Wow.

Lisa Pratt: Talk me into applying. I kept saying, "No, it's just too late." Then finally, one time on a phone call, and Jim, this was three days before the position was going to close for applications, she said to me, "So mom, following your passion and reaching for your dream job is advice you can dish out but you can't take it yourself?" I was so shocked that this 25-year-old threw back at me what I throw at her that I actually said, "You know what, I'm going to apply. I'll never be selected, but I'm going to apply, and for the rest of your life, you're going to say to me, 'I'm so proud of you for applying.'"

Lisa Pratt: Then the unexpected happened, and I've had the most wonderful two and a half years to date of being the Planetary Protection Officer and helping NASA find ways to not contaminate forward or backward. It's a gift that Isabelle gave me.

Jim Green: Well, I got to tell you, I'm so proud of you for applying because I have enjoyed working with you over the last several years. It's just been a wonderful experience for me too.

Jim Green: Well, thanks so much for tagging up with me today to discuss what a Planetary Protection Officer does and how they do it. I've really enjoyed our discussion today.

Lisa Pratt: Hey, Jim I'm just I'm just delighted that you asked and we had a chance. You caught me off guard with a couple of these questions, but the speculation was lots of fun, and go Perseverance.

Jim Green: Go Perseverance. Join me next time as we continue our journey to look for a life beyond Earth. I'm Jim Green, and this is your Gravity Assist.

Credits:

Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper

Source: https://www.nasa.gov/mediacast/gravity-assist-she-protects-other-planets-from-our-germs

[Orionid]

Astrobiologia zaczyna się na Ziemi, poprzez badanie ekstremalnych środowisk biologicznych.

Laurie Barge: Well, hydrothermal vents are basically cracks in the sea floor, where you have seawater that interacts with the sea floor rock, and then it goes down into cracks in the rock, and then it becomes chemically altered. So it's basically a different fluid, then that hydrothermal fluid comes back up out of the sea floor. And when you have these two fluids interacting, you have the hydrothermal and the seawater, they're very different.

https://twitter.com/nasa/status/1291809334842855425

Gravity Assist: Gardens at the Bottom of the Sea, with Laurie Barge (1)
Aug 7, 2020


Astrobiologist Laurie Barge, left, and former intern Erika Flores, right, at the Origins and Habitability Lab at NASA’s Jet Propulsion Laboratory, Pasadena, California. Credits: NASA/JPL-Caltech

Billions of years ago, life may have gotten started at hydrothermal vents, cracks in the sea floor where hot fluids from inside our planet mix with colder ocean water. Laurie Barge, an astrobiologist at NASA’s Jet Propulsion Laboratory, studies how plant-looking mineral structures called chimneys grow from chemicals found at the deepest depths of the ocean. In her lab she has glass vials and bulbs full of different chemical mixtures that simulate undersea conditions. Through careful mixing, scientists can even form amino acids, which are essential building blocks of life. Could similar processes happen in oceans under the ice shells of moons farther away in our solar system, like Europa and Enceladus?

Jim Green: How could we possibly find life beyond Earth if we don't even know how it started here?

Laurie Barge: We don't actually know where the first life lived. There's theories that it could have been on land, underwater in a vent at a high temperature.

Laurie Barge: We really don't know what exists beyond the last ancestor.

Jim Green: Hi, I'm Jim Green, chief scientist at NASA, and this is “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green: I'm here with Dr. Laurie Barge, and she is a research scientist at the Jet Propulsion Laboratory. She's also a co-lead on JPL's Origins and Habitability Laboratory. Laurie is interested in the emergence of life on early Earth and understanding how to look for life out in the solar system and beyond. Welcome Laurie, to Gravity Assist.

Laurie Barge: Thanks. Thanks for having me.

Jim Green: Well, how did you ever get interested in the study of how life may have originated on Earth?

Laurie Barge: Well, actually, I had a more general interest in science when I was little, I just wanted to study space. But when I went to study that in college, I found that I was most interested in the things that address these existential questions like why are we here? And is there life elsewhere?

Laurie Barge: And so I ended up actually doing my thesis about biosignatures. So it was a reverse, it was why are these weird patterns forming and geological and chemical systems that look like life, but are not life? And then after studying that, I thought, "Well, can you go the reverse? Can you say, "Well, if a non-biological system can make such interesting patterns and complexity, then is this a way that you could lead from a geological system into a biological system at some point?" And so that's why I switched over to studying the origin of life, which then also led me into studying Earth's oceans.

Jim Green: So I hear your lab is really fascinating.

Jim Green: What does it look like when you walk in?

Laurie Barge: Well, it looks really different from what you would maybe expect, because we're simulating something that's at the bottom of the sea. But in order to do that, it looks like a mad science project. It's all in what's called a fume hood, because we have to keep the toxic gases away from the researcher. So those get sucked up into the fume hood. And then we have each little ocean vile separate on a stand being clamped up above the ground. And then we have tubes of atmosphere gas coming into each one, because we have to be early Earth, so we can't have any oxygen in there. So we have tubes of nitrogen, and argon, and other non-oxygen gases feeding into each chimney.


At NASA’s Jet Propulsion Laboratory, Laurie Barge and Erika Flores show off solutions that recreate the conditions of the bottom of the ocean billions of years ago. Credits: NASA/JPL-Caltech

Laurie Barge: The chimney itself, it looks like what's called a chemical garden. There's actually this whole other field of research called chemical garden where you can grow these plant-like structures from a metal salt. And they look like plants, but they're completely non-biological. A hydrothermal chimney is also an example of a chemical garden, because it is growing from two solutions that meet each other and it grows vertically. So they look like mineral plumes, small chimneys, and they grow about a couple centimeters high, but of course, in their real environment, they can grow to be tens of meters tall. It's just about what scale do you have as far as, for the fluid to inject into the seawater.

Laurie Barge: So the little chimney is actually connected with all these tubes, all these different things, and even instruments to analyze it as it's growing. So it looks pretty cool.

Jim Green: Your research also focuses on hydrothermal vents. What are hydrothermal vents and where are they, and how do we know how life emerges from around them?

Laurie Barge: Well, hydrothermal vents are basically cracks in the sea floor, where you have seawater that interacts with the sea floor rock, and then it goes down into cracks in the rock, and then it becomes chemically altered. So it's basically a different fluid, then that hydrothermal fluid comes back up out of the sea floor. And when you have these two fluids interacting, you have the hydrothermal and the seawater, they're very different.

Laurie Barge: And that's why you get a lot of chemical precipitation of minerals, but you also get gradients forming.

Jim Green: So when you're talking about gradients in the whole environment, what are you talking about?

Laurie Barge: Well, we're talking about really, just any big difference between the two solutions. You have the seawater and the vent fluid. And there's a couple main differences that lead to important factors, for say, chemistry or life. One is the redox gradient. So this means that the hydrothermal fluid is emitting chemicals that are rich and electrons, things like hydrogen or methane. And so life can use these as fuel. And then the ocean, at least, today has oxygen in it. So that's a great oxidant. And on early Earth, it would have had things like carbon dioxide, which is also an oxidant.

Laurie Barge: And so that's the redox gradient. And then you have chemical gradients. So these are just when you have a difference in the amount of a certain ion or molecule from the inside to the outside of the vent. So things like maybe sodium, or magnesium, or organic material. And then there's also the pH gradient. So this is the gradient of how acidic it is. So the ocean on the early Earth would have been mildly acidic, and then the hydrothermal fluids, some of them are acidic, some of them are alkaline. And so each gradient can vary depending on what type of vent you're in.

Jim Green: These hydrothermal vents actually is a relatively recent discovery. I think the first hydrothermal vent was found when I was in graduate school. So, I mean, this is just fantastic brand new research. But in each of these hydrothermal vents, don't we find life?

Laurie Barge: Yeah, these vents do support life. They support microbial life, but they can also support multicellular life. And it's a little biosphere that's supported by this chemical energy. It's really interesting, because the vent is just giving off chemicals from inside the Earth that are energy sources for life, and life can build an entire biosphere based on this. And it's separate from biospheres fueled by say sunlight. So the discovery of vents really taught us that you can have metabolisms of all kinds and they can be chemically powered by the planet, and then as we learn more and more about microbiology over the subsequent years, we've learned that life can actually use a whole variety of different energy sources. So, whatever there may be available in an environment, there's probably some life that wants it.

Jim Green: Well, you know, since those hydrothermal vents were found, we're now finding hundreds and hundreds of them. Where do we typically look in the ocean floor? Where is the biggest probability of finding a hydrothermal vent?

Laurie Barge: Well, I would think that, I think generally, it's where you know that there's volcanic activity. And so things like the plate boundaries, mid-ocean ridges, things like that. You could expect that there's going to be some chemical alteration. But they can be found in other places, too. And so it can be really hard to predict exactly where you should find a vent. So Earth's sea floor is a very, very big place and it's not completely explored. And so, there's still a lot to look for.

Jim Green: So essentially, these vents don't receive sunlight, they're not powered by the energy of the sun, they're powered by the energy of the planet. But our ocean isn't the only body that has water like that. Where else do we think are hydrothermal vents in the solar system?

Laurie Barge: Well, there has been discoveries of oceans on other worlds and we would like to find out if any of those might also have vents. And to have a hydrothermal vent, you need to have a liquid water ocean, but you also need it to be interacting with the rocky sea floor, because it needs to have the seawater going into those rocks and altering, and then coming back up. And so, basically, the questions for astrobiologists are, is there a rocky sea floor that is in contact with that ocean? And do you expect the ocean to be circulating and undergoing that same chemical process? And then, if it comes back up, what type of gradients do you have?

Jim Green: Now, the study of these hydrothermal vents that you're doing so much in this particular area, is that because the basic idea is that life must have really occurred on Earth in the ocean first, and therefore these hydrothermal vents?