[NASA Gravity Assist] Searching for Life

[Orionid]

1)  What is Astrobiology? With Mary Voytek April (2) 17, 2020
     https://www.forum.kosmonauta.net/index.php?topic=4354.msg155484#msg155484

2)  Life on the Rocks, with Heather Graham (2) April 17, 2020
     https://www.forum.kosmonauta.net/index.php?topic=4354.msg155529#msg155529

3)  Could We Find Billion-Year-Old Cholesterol? With Lindsay Hays (2) April 24, 2020
     https://www.forum.kosmonauta.net/index.php?topic=4354.msg156016#msg156016
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Introducing Gravity Assist Season 4: Searching for Life
April 15, 2020

Hi. I'm Jim Green, NASA's chief scientist and your host on NASA's podcast Gravity Assist.

You know, life on Earth is just about everywhere we look - from the depths of the ocean to even the Antarctic Tundra. Here on Earth, we find that against all odds, life survives and thrives. But what do we know about life beyond Earth? Are we alone?

<a href="http://www.youtube.com/watch?v=SKKvJpjeMJY" target="_blank">http://www.youtube.com/watch?v=SKKvJpjeMJY</a>
https://www.youtube.com/watch?v=SKKvJpjeMJY&feature=emb_title

Life on Earth just occupies a teeny portion of all of time. To me, life seems so inevitable and the universe is so broad and vast, that I can't imagine that we would be alone in all of that space. If we're the only game in town, it's an awful waste of space. We do not know if there is life beyond the Earth. You just have to search and search.

If you've ever wondered if there's life out there beyond our planet, you won't want to miss this season's Gravity Assist. In each episode, I'll be talking with scientists that specialize in the field of astrobiology. I'll be asking them, "How do we define life? What is life anyway? What do we know about how life got started here on Earth and how it developed in this beautiful complexity that we see today? What could life be like beyond Earth and how do we look for it?"

So there are a lot of wild and crazy places that we could search for life. The moons of Saturn and Jupiter are so compelling- Ganymede,Titan, Europa, Enceladus. Life might have existed on Mars in its past and might even exist there today. On exoplanets, because there's a lot.

On average, there's an exoplanet for every star in the sky and for every 10 stars there's one that might have liquid water oceans. Advancing the technologies for one helps us look for it in any place that we might be looking. Here at NASA, we have a fleet of spacecraft going out into the solar system and beyond and a lot of fabulous scientists that are piecing together this puzzle from the observations these missions make.

Join me on this journey to find out what's out there. Tune into gravity assist wherever you get your podcast.

Source: https://www.nasa.gov/mediacast/introducing-gravity-assist-season-4-searching-for-life

[Orionid]

Gravity Assist: What is Astrobiology? With Mary Voytek (1)
April 17, 2020


Astrobiologists think about not only where in the solar system life could exist, but also which planets orbiting other stars could be habitable. Credits: ESO/M. Kornmesser

How did life originate and evolve here on Earth? What form could life take elsewhere – and where else could life survive beyond our planet? These are questions that scientists called astrobiologists tackle every day. By using space telescopes, doing laboratory experiments and studying extreme environments on Earth, astrobiologists hope to uncover new insights about what it means to be “life” and get more clues to the ultimate question: Are we alone in the universe? Mary Voytek, head of NASA’s astrobiology program, discusses in this episode.

Jim Green: Are we alone? What is NASA doing to answer that very important question?

Jim Green: Let's talk to one of the top astrobiologists in the country.

Mary Voytek: As we look for unusual life here on Earth and life elsewhere, we look for the unexpected.

Jim Green: Hi, I’m Jim Green, NASA’s Chief Scientist, 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. Mary Voytek, she's the lead scientist for astrobiology at NASA headquarters, and she manages the entire astrobiology program for NASA. Welcome Mary.

Mary Voytek: Thank you so much for asking me to do this, Jim.

Jim Green: Well, you've been doing this now for many years and the concept of astrobiology is really coming on strong. We talk about it all the time in science, but what really is astrobiology, what does it mean?

Mary Voytek: NASA defines astrobiology as understanding how life emerged and evolved here on Earth and where it could possibly exist elsewhere beyond Earth.

Jim Green: When I talk to the public and I say, "NASA is looking for life beyond Earth," the first thing they think of is, "Wow, we're looking for little green men." But are we really doing that?

Mary Voytek: So NASA’s strategy for looking for life has been informed by what we understand about Earth.

Mary Voytek: We think there's been life on this planet for maybe about 4 billion years, but that's been single cell microbial life. It's only been in the last few hundred thousand years or several hundred million years that we've had forms of life that would be more recognizable and would be able to be seen without the unaided eye.​

Mary Voytek: So most of the time on this planet, the only life that was here was microbial, single cell, very, in terms of form and structure, very simple. And so in terms of searching for life, just in terms of probabilities, it is more likely that we would find microbial life on other worlds.

Jim Green: So what are the kinds of things that we're doing in terms of looking for life here at Earth?

Mary Voytek: One of the most important things is an understanding how you go from a planet where there's no life to a planet that is teeming with life, is to look at those transitions and the condition of the planet, as well as how it affects the processes that are steps towards the emergence of life. So we're looking at things like, what are the physical and chemical conditions on early Earth that would be conducive to the production of molecules that end up becoming extremely important in life? And that includes molecules that can provide energy, as well as molecules that can be built on to provide structure and function, and basically the components that we see in life today.

Jim Green: Well, one aspect has really excited me, and that is looking for life in extremes. You look out into the solar system and it's hot or it's really cold, or the environments are so much different than ours. And so extreme environments are really important. And I know we do that here on Earth.

Mary Voytek: Absolutely. And in fact, in addition to understanding the steps towards life emerging and looking for the earliest signs of life here on Earth, we also want to understand those limits to life because as you said, the environments in our own solar system beyond Earth are not Earth-like, they're not the conditions that we all find pleasant. It's not the lovely climate of California out on those planets, and so we need to understand how life can actually persist in something that is beyond our comfort zone.

Mary Voytek: So our comfort range is, we know what room temperature is, we know what standard pressure is. And so organisms that seem to thrive and enjoy or love conditions that are more extreme than that or outside our comfort zone are called extremophiles. We can certainly live in cold temperatures, but not without putting on cold weather clothing and building shelters and generating heat for ourselves. But there are organisms that don't have coats, microorganisms that aren't hooked into the power grid and generating enough heat to live, and they're called psychrophiles because they love the cold.

Mary Voytek: And then there are organisms that really love the heat that can live at temperatures above the temperature at which water boils, so that's 100 degrees C. And so these allow us to start looking for environments that would be suitable to support life, even if it's extreme life.

Jim Green: Well, one of the common threads between all those extreme environments is water. No matter where we go, where we find water, even in small amounts, we have the opportunity to find life.

Mary Voytek: Yeah. We always struggle amongst scientists with definitions of life. And in fact, I usually like to say if you ask 100 scientists what is life or how to define life, you'll get 120 definitions. But one thing is really common to all definitions is it requires a solvent.

Jim Green: Mary, what do you mean by solvent?

Mary Voytek: Well, in chemical sense, it's a medium or a solution that allows reactions to take place, and so it facilitates transfers of electrons and modifications to chemistry. It also provides a liquid, also provides structure, and we are mostly water. And so that solvent or that liquid actually is responsible for our structure as well.

Jim Green: So we are what we eat and at the end of the process--

Mary Voytek: We are what we drink.

Mary Voytek: Here on Earth, the life that we know requires water. It's how it moves materials around, it allows the fluidity within cells so that cells can actually function. And so that has been one of the primary strategies at NASA for looking for places that could support life. So we go to extreme places here on Earth, like the dry valleys of Antarctica or the Atacama Desert where to the eye, it appears as if there is no water, but even a tiny bit of water, as you mentioned, life can take advantage of.

Mary Voytek: And so as we go beyond Earth, we're now then looking at environments on say, Mars that might have the same level of water that we see in these deserts here on Earth.

Jim Green: I remember the day you came into my office and we had this great discussion on how we would define life and how that should be viewed and a definition that would encompass all kinds of different life, things that we can't even imagine right now, life not like us. You told me it had three basic parts. What were they?

Mary Voytek: Well, of course it required a solvent to support a particular type of chemistry. It requires a mechanism to acquire energy, because everything requires energy to do anything. And then it had to be able to reproduce. I guess I'm going to extend it a little bit to four.

Jim Green: It sounds like it.

Mary Voytek: It needed to be able to evolve because our environment is not static. And as Earth has changed, life would not survive if it weren't able to adapt and evolve to actually be able to thrive in the new environment.

Jim Green: Well, I know you were really excited about that definition because it's all encompassing in the sense that it doesn't require that it be water or that it requires a carbon-based life form. But I was in the doldrums because indeed I can't run out and build an instrument that measures reproduction and evolution and then a have that operated on some planet. So that's really tough. But the water theme for us, for life like us, or the liquid aspect of it really helped us start a process of looking for life beyond Earth.

Jim Green: Well, why should we care about this particular topic?

Mary Voytek: I'm going to break down the question to something a little bit different, which is, are we alone? That's a really compelling question. It's philosophically important, it challenges our identity as human beings. And I think people in general are just fascinated by that question and they want to have that question answered.

Jim Green: Yeah. Me too. Right.

Mary Voytek: In addition, we now know more about how our own cells function. Some of the work that we do in astrobiology informs us about how cancerous cells may have actually played a role in a positive way towards evolution because it's kind of growth out of control, and maybe that's what you need to initially establish yourself on a planet.

Mary Voytek: And so it has all these ramifications for just understanding biology here on Earth. And I have to say, I'd be extremely excited for us to find something that was different than life on Earth because in science, you learn often the most when you find something to contrast.

Mary Voytek: And so any kind life is going to be exciting, but finding something that is very different would be really exciting as well.

Jim Green: Even here on Earth, we're looking for that. We're looking for something really different, something, maybe not carbon-based and maybe not requiring water, but still another liquid. Where are we in that search and have we found anything?

Mary Voytek: Well, I like to tell people that when we define life or we understand life here on Earth, we're looking at the winner. So the very beginning of life as it started to emerge, there were probably a lot of different solutions to what kind of solvent, what kind of molecules were important for structure. What kind of energy was it acquiring? What form it took? What elements it actually may have used. And at some point in time as life continued to reproduce and evolve, there was a form that was the most successful here on Earth given Earth's conditions. And we call that the last universal common ancestor. And at that point, most of biology, if not all of biology have those basic things.

Mary Voytek: But at the same time, there could be less successful organisms that exist still here on Earth, but the challenge in finding them on a planet that is overwhelmingly populated by all of those successful forms that come from that winner is a real challenge.

Mary Voytek: And so looking in extreme environments allows us to start looking for that.

Mary Voytek: We think about at some point in time on Earth, life became so predominant that it affected planetary processes, and you start seeing evidence of it. So you don't see growth and reproduction, but you see a change in the composition of our atmosphere. We went from an environment that was anaerobic to an atmosphere dominated by oxygen, and that was because of microorganisms. And so as we look for unusual life here on Earth and life elsewhere, we look for the unexpected. We learn more and more about how planets and planetary bodies function, we have an expectation of what their surfaces will look like and we understand what we expect from an atmosphere if it has one.

Mary Voytek: And then we look for something that just isn't what we expect. We look for a disturbance in the force, you might say, something that is just unusual that we can't explain any other way. And that's where we begin. And that's to some extent, in our enthusiasm for searching for life, some mistakes we've made in the past where we thought we understood what we were looking for and didn't spend quite enough time dispelling any other possible explanation.

Mary Voytek: But we're much smarter now and that's exactly how we take how we approach the search for life.

Jim Green: Well, we've done so much work in this area and there's so much detail, why haven't we found life yet?

Mary Voytek: That's a really good question, and I pause because it just swims around in so many ideas in my head for why that's possible. And one is, of course as we've already discussed, the challenge of, if life is not as we know it. And so again, how do you look for life as we don't know it? The other issue is, it is pretty clear that based on life as we know it, that Earth is the premier planet. It is perfectly situated in relationship to its Sun, it's got a magnetic field that protects it. It's gotten many, many environments across the entire surface and into the subsurface that can support life as we know it. It is just an incubator, a perfect incubator.

Mary Voytek: And so as you start looking into environments, even on Earth where say nutrients are limiting or there're extreme physical conditions, you notice that the number of cells decreases. And so as we look beyond Earth and we look at places like Mars or we look even beyond to the moons of Saturn and Jupiter, these environments are much more extreme than Earth, much less hospitable. And so just because of what we know about Earth, the inhabitability of an environment can control how much life you see, we would predict the amount of life on any of those other bodies is going to be very dilute, there isn't going to be much of it.

Mary Voytek: Finding something very small, it's like looking for a needle in a haystack. Relative to the bulk of materials on these bodies, life is going to be a small component. It's going to make less of an impact on the environment. And so detection limits are essential. And really, really refining where we go to look for life is going to be essential because in biology, one of the things we do is grab a sample and grind it up and then analyze it. We can't take a giant sample of Mars and just grind it up and hope we find a cell in it. We have to be very smart about where we think it might be and figure out how we can most effectively look at that very, very small signal.

Jim Green: Well, there's another dimension to this that I've come to realize and appreciate, and that dimension is time. When we go out to planets and we're looking at their current environments, because the solar system is 4.6 billion years old, things have changed over time. And so that dimension is really important. So how do we think about how life might exist in the past on other objects?

Mary Voytek: Particularly now that we have exoplanets to look towards, the possibility has really exploded in terms of what environments might support life. And one of the strategies for people who are interested in exoplanets has been to look at the environments on Earth over time. At the very beginning, the solar system was kind of a violent place to be situated, with bombardments from objects out there like asteroids and comets. And that changed the Earth both on its surface and its atmosphere.

Mary Voytek: There's also just the differentiation or the evolution of the planet itself. And it turns out that's a huge, huge deal for organisms dealing with oxygen. On one hand, of course we know we can't live without it, but when that change first happened, it was a toxin. Oxygen is a way that we actually get rid of organics. Hydrogen peroxide is an oxygenated compound that we use to sterilize things. And so organisms had to figure out how to deal with that first. And then as a result, once they were able to adapt to oxygen, it turns out that oxygen is a fantastic molecule to pair with other molecules to actually generate energy.

[Orionid]

Gravity Assist: What is Astrobiology? With Mary Voytek (2)


Mary Voytek, head of NASA’s astrobiology program, with NASA Chief Scientist Jim Green. Credits: NASA

Jim Green: So this really exciting. What do you think are some of the best payoffs that we've gotten by making this kind of research viable for NASA?

Mary Voytek: Well, I think that there are a number of areas that we've had a major impact, as NASA has in general. A lot of our scientists that we fund to work on origin of life questions are also doing medical research and they're quite related. I also mentioned synthetic biology. And synthetic biology is where basically we look at what organisms have managed to do on their own and modify them to our own needs to make them do things that we need to have them do.

Mary Voytek: So for example, bio-remediation. The best way to clean up oil spills or contaminants in groundwater in particular is to apply organisms that can use those contaminants either as an energy source or food for making materials in the cell. And in the process, they convert it from something toxic to something that is benign. In addition, we have an instrument that we developed from a researcher out at Ames, Dave Blake that's called CheMin. It looks at the mineralogy of systems and their oxidative states.

Mary Voytek: And one of the things that's currently being used for is... Well, there are two interesting ones. One is it's used in the detection of counterfeit drugs, which is a gigantic problem for the World Health Organization. And in addition, they've used their instrument to detect fraudulent artwork. And so you can use this to understand minerals that go into paints that weren't present, say during the Renaissance. It's important in terms of paint restoration, but also in detecting actually, you may all know that that canvas is for painting were reused multiple times, and so you might find a Rembrandt that has multiple layers of different paintings.

Mary Voytek: And some of this, the CheMin was the tool that could be used for the materials that were generated in that paint, and any kind of change may lead to other kinds of detection for looking for things like that as well.

Jim Green: And that instrument is on Curiosity on Mars.

Mary Voytek: Yeah. Go Curiosity.

Jim Green: Right. And it’s doing fantastic. Well, where are you most excited to look for life and why?

Mary Voytek: I have two answers to that. One is in our own solar system. As the head of the Astrobiology Program, I'm excited about all places, but I'm very, very much intrigued by the news-

Jim Green: You love all of children equally, as I like to say.

Mary Voytek: You know. Absolutely. I love all of my habitable environments equally. I'm very excited to learn more about the moons of Saturn and Jupiter. I just think that between the possibilities with Europa and Enceladus and the fact that we are sending out missions to study them better and just how bizarre Titan is, which is a moon of Saturn, with the only other body in our solar system that has liquid on the surface, but that liquid is methane and ethane and it's not water. And so what kind of biology can you expect from something like that? If we find life there, it's going to be, I just can't even imagine, it's going to be so different than life here on Earth.

Mary Voytek: One of the most amazing discoveries we made in the end of the '70s, so right around the time that Viking had landed on Mars looking for life, was discovering weird life here on Earth. And that was life that we found kilometers away from the surface at the ocean floor, at hydrothermal vents systems. And this was the first time we discovered that life could be supported by energy other than the Sun. Up until that point, we thought every single thing on the planet ultimately derived from energy provided by the Sun, but we find this oasis of really odd organisms supported entirely by chemistry, chemical reactions that can generate the energy necessary for organisms to thrive.

Mary Voytek: And so on these ice-covered oceans, we expect that we could possibly have the same system. We have evidence, at least in one of them, that we definitely have hydrothermal activity, that is, water interacting with rock of the planet or the planetary body at higher or elevated temperatures. And that causes a certain kind of chemistry than on our own planet has led to supplying molecules necessary for the energy that can support life. And so we think that that could be happening on either Saturn's moon in Enceladus, or Jupiter's moon, Europa.

Mary Voytek: And then of course, the possibilities that have recently in the last five to 10 years with the number of exoplanets we've detected. Oh my goodness, it's almost any planet you could imagine. I feel like it's almost, we're at the point of having a video game or a game where you just dial different things and you create a planet and it could support life, "Oh, I want it a little warmer. I want it a little colder. I want more water, less water. I want to have this mineral present or not."

Mary Voytek: I just think that the possibilities are just astronomical and I mean that intentionally.

Jim Green: That's a really neat idea because as you turn around and turn those dials and create that planet, that planet exists out there somewhere.

Mary Voytek: It does, I think.

Jim Green: That's right. I just never thought of it that way, but we've got like four thousand planets that we've identified and that number is just going to increase over time.

Mary Voytek: Well, those are ones we've identified. If you go by what we predict, if you look up in the sky now, we're not looking at stars anymore. We're looking at solar systems.

Jim Green: So Mary, with all this said, what do you think, are we alone?

Mary Voytek: I think, absolutely not. I believe that, I'm not sure when we're going to find life, but I am certain that there is life beyond earth.

Jim Green: Yeah. I am too.

Jim Green: Mary, I always ask my guests to tell me what was the event or person, place or thing that got them so excited about them being the scientists they are today, and I call that event a gravity assist. So Mary, what was your gravity assist?

Mary Voytek: I think I can identify a person that helped me, pushed me forward, and that was my mom. And although she was not a scientist, she was extremely bright and very interested in the natural world and very interested in science fiction. So I have memories as a child going to the beach in the summer and being encouraged to set up aquaria and to study the organisms in the ocean. And I have memories of every Thursday night, I think it was, I might be wrong about the day, assembling with my four other siblings to watch Star Trek on TV with the entire family.

Mary Voytek: And so I think that the very force of personality that my mother had, the hope, the imagination is what really sent me into science and really nurtured and stimulated my curiosity that led me to where I am today.

Jim Green: Mary, let's say one of our scientists calls you up and says, "I found it. I think I have found life on this planet," what do you do next?

Mary Voytek: So extraordinary claims require extraordinary evidence, and that comes from our most famous and inspirational scientists, Carl Sagan. And in fact, this happened to us in 1996 -- a scientific group out of Houston came to us with evidence, four lines of evidence that they thought that they had actually found evidence of life in a Martian meteorite. And very good scientists, excellent, reputable scientist, respectable scientists said they had the evidence and it came out in a peer-reviewed publication, and after that the entire scientific communities started examining it and challenging it.

Mary Voytek: And one of the things that we discovered is you can do great work, but you can still be wrong. And in fact, I like to say that astrobiology is 60 years of doing research, proving ourselves wrong as we move towards understanding what life is and how we can detect it. And so the first thing that I would do is find out what that evidence is. We'd make sure that it was put to the test by other scientists before we would do anything with that. So the peer-review process and publications is the start. We've learned too that some people can be so enthusiastic that we might even need greater challenges, but we would basically take it to the global scientific community and put it to the test.

Jim Green: Okay. And then if it turned out to be true?

Mary Voytek: Once I stop screaming with excitement, we would go back onto... I think that a lot of us have talked about what would be the next step.

Jim Green: Well, we certainly wouldn't keep it a secret.

Mary Voytek: No, absolutely not.

Mary Voytek: One of the things Astrobiology Program does is, we have talked to individuals about what it would mean to you to find life, does it challenge your religious beliefs? Does it challenge how you think about yourself, or whatever? Are you frightened by the concept?

Mary Voytek: And so, it would be really important to think about how to deliver that messaging, and I think that there is tremendous excitement that we could convey. I think we can convey hope and leading to a better understanding about ourselves. I think we'd also need to know like, "So, where did you find it and how can we find out more?"

Mary Voytek: Initially, after I stop screaming myself, it's like, "I want to get some more of that. I want to go to wherever that came from. I want to... " More work, more science, more characterization, more to understand.

Jim Green: It's the next set of questions you now want to ask.

Mary Voytek: Absolutely. Absolutely. That's what I'd do after I stop screaming. What about you Jim?

Jim Green: Oh, what would I do?

Mary Voytek: Yeah, if it's you.

Jim Green: I'd be screaming too.

Jim Green: Well that’s fantastic, and Mary, thanks so much for joining me today and talking about, of course, one of my favorite subjects too, astrobiology.

Mary Voytek: Thank you so much, Jim. This has been a blast.

Jim Green: You're very welcome. Thank you. 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: Emanuel Cooper
Last Updated: April 17, 2020
Editor: Gary Daines

Source: https://www.nasa.gov/mediacast/gravity-assist-what-is-astrobiology-with-mary-voytek

[Orionid]

Gravity Assist: Life on the Rocks, with Heather Graham (1)
April 17, 2020


Illustration of DNA strand, adapted from a Creative Commons image. Credits: Nogas1974 CC BY-SA 4.0

To study the history of life on Earth and look for it beyond our planet, scientists in the field of astrobiology look for signs called “biosignatures.” NASA Goddard researcher Heather Graham discusses some of the oldest evidence of life on Earth and what scientists are searching for when they look for biosignatures in ancient rocks. By looking at what life on Earth was like millions and even billions of years ago, astrobiologists can make predictions about what signs of life could be hiding in the rest of the solar system and beyond.

Jim Green: Life starts with chemicals. The chemistry of life is so important to understand.

Jim Green: So how do we know it's life, if it's life like we don't know it?

Heather Graham: There's a lot of ways that life could be different, but not related to life on Earth.

Jim Green: Hi, I’m Jim Green, NASA’s Chief Scientist, 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. Heather Graham. She is an organic geochemist at NASA Goddard Space Flight Center. Heather has a profound curiosity about the natural world, the history of life, the vast connections between biotic and abiotic systems, and what evolution can tell us about our future. Welcome to Gravity Assist, Heather.

Heather Graham: Thank you so much Jim.

Jim Green: Well first off, what the heck is a biosignature?

Heather Graham: So a biosignature is just a physical indication of past or present life. That can be something as simple as a bone that a paleontologist might find, a footprint, an imprint, on the environment. Or a chemical compound that's highly specialized for life.

Jim Green: So how do we know if a biosignature actually came from life? Can we be fooled?

Heather Graham: Oh yeah. That's a probably the most important part of biosignature science is making sure that you are looking at something that came from life, and not being fooled by something that can be made by a physics, by nature, by geology, by abiotic chemistry.

Heather Graham: There are a lot of things that we associate with life that are actually very common, being made out in stars. A lot of the chemicals that we associate with life are really an inheritance from the universe. We also have to be very careful to keep our work clean, so that we're not contaminating it with contemporary life when we're trying to understand past life.

Jim Green: Biosignatures require certain chemicals. Is there some underlying composition that you look for in a biosignature?


Astrobiologist Heather Graham holds a 600-million-year-old fossil. Her tattoos represent high-speed particle collisions. Credits: NASA

Heather Graham: Yeah. So it really depends on where you're looking, and what you're looking for. For example, a really common biosignature that we hear about a lot is DNA. And that's something that's universal. Every organism has it, so it's easy to say, "Oh yes, this is definitely from life. This is a molecule that's too hard to make without biology being involved."

Heather Graham: But DNA is very ephemeral. It goes away quickly in nature. It's broken down by other organisms, and reused very quickly. But there are other chemical compounds that last for a really long time, especially in the geologic record, in the rock record. And those are the things that we can look at as being a more robust signal of life on long time scales.

Jim Green: So getting down to the basics, the really important chemicals, carbon seems to be one. If we look at what we have inside us, it's carbon, hydrogen, oxygen, nitrogen, phosphorous and sulfur. So are those the fundamental compounds we ought to be looking for?

Heather Graham: So those are the fundamental compounds that we associate with life on Earth.

Jim Green: Life as we know it.

Heather Graham: Life as we know it, correct.. The kind of work that we're doing here at Goddard, and the research group that I'm involved in, doesn't always presuppose that though. We're interested in biosignatures that might not just be about those particular elements. Or more importantly, other elements that might be biosignatures as well.

Jim Green: How do we figure that out? How do we figure out what are the more important elements?

Heather Graham: That's really from just observing nature in its completeness, in its totality. Not just by looking at life, but by looking at nature in context of its environment to understand what it's taking from a chemical system to build itself, what it's eating, what it's respiring, breathing out, what the by-products of its metabolism are. And then you can track down what are the important things that are moving through a system. And that movement is the essential signature of biology. If something's static, it's unlikely to be involved.

Jim Green: So the concept of you are what you eat is true?

Heather Graham: Absolutely.

Jim Green: So we actually pull things out of what we eat, and plug them into our body.

Heather Graham: Yep. So we take carbon from all these other sources. And interestingly though, carbon dioxide is our major by-product. We all breathe it out. But there are lots of organisms that don't do that with carbon. They use metals and other strange things. And we find all these metals in certain places in the geologic record. And even though we don't see that organism, we know that this is something it left behind.

Jim Green: So where do we find biosignatures?

Heather Graham: Usually, when we're thinking about biosignatures, we think about the rock record, we think about geology. And really, that's just because that's a really stable repository. To find a biosignature, you have to find a place where a molecule or a part of an organism is protected from degradation. So, we think of places where there's not a lot of oxygen, since most other critters that would want to eat that organism are going to be using oxygen.

Heather Graham: We look for rock, areas of sediments, that have been protected from oxygen in the atmosphere. And the rock record’s interesting, not just for people who are interested in land, but a lot of the rocks are actually old ocean. It's all the ocean sediments. So we can peer into past ancient oceans just by going to certain rocks on Earth.

Jim Green: Well you brought a really nice friend with you. It's a fossil. What is that?

Heather Graham: So this is a really special fossil. This is from the Ediacaran period. That's about 600 million years ago. And this was a time in Earth's history when biology got really experimental. And during this time period, we find all sorts of crazy organisms that only exist during that time period. Biology was trying just all sorts of body plans, and ways of living on the surface, or just below the surface, in really neat ways.

Heather Graham: And these kinds of fossils are only found in a couple of really special places on earth, Nevada and Namibia.

Heather Graham: So this fossil, as you can see, there’s these long tubes, and there're ridges along them, and they crisscross. And what's sad is this piece that I brought to you is only about the size of my palm

Heather Graham: And what you'll see is there's all these tubes weaving back and forth over each other. But not in a random way, in a very special pattern. And that's part of what makes us realize this is biology, and not just rocks that happened to fall in a really interesting pattern. This has intentionality and there was energy put into a system to leave this texture.

Heather Graham: This strange structure, there's a couple of different ways you might be able to try and explain it. Maybe it's a texture on a rock from a biofilm. Maybe it was a tube worm that was living below the surface. But what's really important about this is we don't have any physical way, without biology, of making a pattern like this. And that's what makes it a biosignature. You can do all sorts of experiments with different sizes of rocks, and different chemistries of solution was of water, but you'll never make something that looks like this.

Jim Green: Yeah, it looks creepy.

Jim Green: So I heard there's like 4,700 minerals on earth, and about 300 of them could only be made by life.

Heather Graham: Yes, absolutely. So I know I am a chemist, so I'm biased towards organic chemistry and I'm giving a lot of examples of organic chemistry that are biosignatures. But really, there are lots of minerals that are biosignatures as well. There's a lot of great work that's been done to show what minerals you absolutely need.

Heather Graham: For example, oxygenic life, the kind of life that made oxygen, all the algae in the ocean that made oxygen. There are minerals that would only be associated with those really high levels of oxygen, that those organisms created. So if those organisms never developed on another planet, we would be unlikely to see many of those minerals on those planets.

Jim Green: How long do these biosignatures last? Once they're in the rock, is that it?

Heather Graham: No. Actually, one of the real arts of biosignature science is knowing what things look like when they break apart. Unfortunately, a lot of the chemical compounds that we use as biosignatures don't last in that state that your body or another organism's body made them. They break down in very particular patterns. And so, we find those degradation products in the rock record.

Jim Green: So once life is created, and it decomposes, you end up with the parts. And so figuring out, do you have all the right parts, or even some of those parts, may or may not be preserved over time.

Heather Graham: Yeah.

Jim Green: That ends up being a real problem. So what kind of tools do you use to really identify these parts and pieces in biosignatures?

Heather Graham: Yeah, this is a real puzzle. So this is the kind of area we would really think of as interdisciplinary science. When I'm looking at a particular sediment for example, I'm looking for particular compounds, I'm taking a lot of information that I've learned from other geologists that have described that rock. So I will know something about, was this rock once a lake? Was it the ocean? Was it buried and heated? So I'll have a lot of information from geology to help me direct those tests about what sort of molecules I'm likely to find.

Heather Graham: And the other important thing about these molecules that we think of is biosignatures that are being preserved in the rock record, is there an example of a community. They're usually not just one particular organism, you're looking at a habitat, you're looking at a whole bunch of different metabolisms. So you're really not just saying, was there life, was there not life, but you're getting a sense of what the ecosystem was.

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Gravity Assist: Life on the Rocks, with Heather Graham (2)


Astrobiologist Heather Graham with NASA’s Chief Scientist Jim Green. Credits: NASA

Jim Green: Another thought I had, relative to biosignatures in rocks, is a structure. A structure that, how geologically could that have possibly have happened? Like a stromatolite. So when we study biosignatures, how does that help us think about the origin of life here on Earth?

Heather Graham: Yeah, that's really interesting. So a lot of these chemical compounds that we're thinking of don't really last on really, really long timescales. And when we’re thinking about something like the origin of life, a lot of what we're looking at is physical structures in the rock. Really old evidence of cells, really old evidence of biofilms, which are just big accumulations of microbiota together.

Heather Graham: So we're looking for those physical things in the oldest rocks. And that's where textures and rocks become really important. And also something that you want to be able to make sure that those textures aren't something that nature makes all by itself without biology being involved.

Jim Green: So the key to finding life way in the past. Is to start looking at the old rocks. Well, how old are the rocks here on Earth?

Heather Graham: So that's a bummer about Earth, is that most of our rocks have been recycled-

Jim Green: Oh no.

Heather Graham: And heated, and cooked, and moved, and washed with lots and lots of water. So it's really hard, actually. We think of Earth as being this life saturated planet. And so, it must be so easy to find life. But when we look in the deep past, it's actually hard, because much of that evidence of life has been destroyed by tectonics, by the planet moving around. We're a very dynamic planet.

Heather Graham: So we have to look for what we call quiescent parts of the planet. These are old cratons, the oldest rocks on earth that are up in Canada and Greenland, and places like that, where we find really interesting textures in the rock. And we like to think that those are probably the earliest forms of life. And then that gives us a sense of, what was the chemistry in that early ocean? What was the planet like? And that gives us a sense of the kind of chemistry that was possible.

Jim Green: So just recently, a team from the Mars 2020 Rover group, this is the group that is going to be looking at the rock record from Mars, trekked out into Australia. And I was wondering, why are they going to Australia for a meeting? Well, they're out in the middle of nowhere in Western Australia, and they went to the Australian chert.

Heather Graham: Cool.

Jim Green: Yeah, so-

Heather Graham: Jealous.

Jim Green: And it's a trek, let me tell you. But that's old rock.

Heather Graham: Yep.

Jim Green: Yeah. So what do we know about that Australian chert?

Heather Graham: Yeah, so those are some of the really old rocks where we find the oldest evidence of life. What's really special about some of those rocks in Australia is, you can find really old evidence of microbial biofilms, these mats, microbes that form these layers and they grow up, up, up upon each other in these layers. And that's a stromatolite, like you mentioned.

Heather Graham: And what's really interesting is, you can see living examples of those right off the coast in Australia. So it's such a special place, to be able to have that window into the deep past, and then see something that's contemporary, that still has the same lifestyle. And is conducting its biology in pretty much the same way for billions of years. It's a really special place.

Jim Green: Yeah. In fact, when they measure the date at these rocks, they find they're 3.6 or 3.8 billion years old.

Heather Graham: Yeah.

Jim Green: But yet, we know the earth is 4.6 billion years old. So there's nearly a billion years record that we've lost.

Heather Graham: Yeah. And the really sad thing is... Because that's our earliest evidence, we know that somewhere in that time period between formation and that 3.8-ish number that you give, that's the exciting part. That's when life evolved, and we don't have really anything to go on there. And that's where experiments in the laboratory can become really illustrative for giving us a window, and giving us something to imagine for that past.

Jim Green: Well, this is where Mars comes in a really neat way, because it doesn't appear to have had some plate tectonics, but not like Earth. And it appears to have been a blue planet like earth early on, but then went very arid. And so maybe the record of life starting, perhaps, on Mars before 3.8 billion years, is attainable in the rock record there that we can bring back.

Heather Graham: Yeah, that's what's really exciting, is: It hasn't had that heating and cooling and moving and crushing that Earth has. And that really can tell us a little bit about why we choose to go the places we go on Mars. That we're looking in these sediments, that we know were buried once upon a time. And if there is something organic there, we're looking in the best places to find something that wasn't exposed to the surface where it could be altered.

Jim Green: So, what's an agnostic signature of life?

Heather Graham: So that is a biosignature where we're not presupposing a connection to Earth biology.

Jim Green: A carbon-based life, like we know it?

Heather Graham: That could be one or it could be carbon-based life that has different informational polymers besides DNA, something like that. There's a lot of ways that life could be different, but not related to life on Earth. And these kinds of studies get really interesting as we're starting to move farther and farther out into the solar system, where there's less and less likelihood that we're related to creatures out there, if they exist.

Jim Green: So do you think we're alone in the galaxy? Do you think life is confined to just Earth?

Heather Graham: I tend to think not. And I base a lot of that on probability. This is another area of expertise that there's lots of people working in biosignatures, and that's the kind of people who think about statistics in likelihood and probability. And it's rare you see something as a one-off in nature. If something works, it usually happens again and again. And so I just can't imagine that we're the only instance of that kind of unique chemistry happening.

Jim Green: So if you think we can find life beyond Earth, where do you think we'll find it?

Heather Graham: Where? Oh, that's interesting. Boy--

Jim Green: In other words, will we find it first in the solar system? Or will we find it in exoplanets first? Planets around other stars.

Heather Graham: I would tend to say that we're probably going to find something unambiguous in the solar system first. And I would say that's really just because for this kind of evidence, you really do need a bunch of different ways of viewing the problem to be convincing. We can't just find one molecule and say, "Oh look, that's life," because you need to be able to see it in context.

Jim Green: So I noticed you have some really unique tattoos. Just long streaks that are emanating from particular points. What are they?

Heather Graham: Yeah, these are high-speed photographs taken from inside a bubble chamber where they were crashing particles into each other in a very particular way to see what kind of other particles are made. And this is imitating processes that happen in certain kinds of stars that make light that has mass. So light from our star is massless, but that's not always true. And I got these tattoos because light was something that was a big part of my PhD work. I actually looked at biosignatures to tell us about light harvesting molecules and photosynthetic organisms.

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

Heather Graham: Oh, I think if I think of any person, place or thing, the place that immediately pops to mind is the community college that I went to, Santa Monica College in LA. It's a really great place, and I think what made it so great is I got to take so many different classes. There's all these different people who work on biosignatures, and you need to have a really firm grasp of physics and geology and chemistry and math.

Heather Graham: And that's something I was able to do at this community college because I had the grace to just explore every topic I wanted to. I took every, every science class they had. I took field ornithology. And I had a wonderful organic chemistry professor there, Jamie Anderson, who just pushed me into every research opportunity he could find. And I think if I hadn't been given that allowance to have all that curiosity, I wouldn't have the background I really benefit from in biosignature science.

Jim Green: You had mentioned to me earlier that you were the first one in your family to go to college. How hard was that?

Heather Graham: Yeah, I am the first person. And I think it's hard because I don't think it was something I ever expected I would do. I didn't actually go to college until I was an adult. And I'm not saying that people that are 18 coming out of high school aren't adults, but I was a real adult. I was 30 when I went to college. And I think it really changes the intention, and how you approach your studies. I wasn't doing it because my mom and dad told me to. I was doing it really because these were things I wanted to know.

Heather Graham: This was interest that I had. And I took it really seriously because I didn't have any examples in my family of how to do this. And I was really helped by a lot of wonderful professors. And when I think about the way I approached it, and that curiosity that I brought to studies, there's a saying by an old author, Charles Baudelaire, "That I sought the why of it, and turned pleasure into knowledge."

Jim Green: Well, thanks so very much. This has just been a delight, and you're a wonderful biosignature.

Heather Graham: Oh, why, thank 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: Emanuel Cooper

Source: https://www.nasa.gov/mediacast/gravity-assist-life-on-the-rocks-with-heather-graham

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Gravity Assist: Could We Find Billion-Year-Old Cholesterol? With Lindsay Hays (1)
April 24, 2020



When we search for life beyond Earth, we have to figure out what we could measure that would tell us that life was, or is, there. And the starting place for that search must be Earth itself, the only place where we know for sure that life has lived. Every rock tells a story, and so does each fatty acid called a lipid. Your cholesterol, which is part lipid and part protein, could last for billions of years, and contains the information that you are a mammal. Could we find lipids beyond Earth? NASA astrobiologist Lindsay Hays explores this and other topics in her research. She also discusses places interesting for the search for life in our solar system and beyond.

Jim Green: When we go look for life in the universe, what are we looking for? Did you know your cholesterol could last for billions of years?

Lindsay Hays: It's a really great way to understand, sort of, the history of the microbial life on this planet, since they don't always leave fossils in the way that dinosaurs do.

Jim Green: Hi. I'm Jim Green, Chief Scientist at NASA, and this is Gravity Assist. This season is all about the search for life beyond Earth. I'm here with Dr. Lindsay Hays, and she's the deputy program scientist for the astrobiology program at NASA. Welcome, Lindsay.

Lindsay Hays: Jim, I'm really glad to be here.

Jim Green: One of the things that the astrobiologists do is they really look at the history of life here on Earth. Now, why is that important for us to do that instead of just go looking for life beyond our Earth?


Lindsay Hays is an astrobiologist at NASA who is interested in the idea of looking for fatty acids called lipids beyond Earth. Credits: Lindsay Hays

Lindsay Hays: It's our one example of life that we know of. And so it's really important that we understand not just what life looks like on this planet today, because it's our only example, but also what life looked like in the past on this planet, how we got to this point is a really important way… it's a really important thing to understand, how mass extinction events or mass radiation events, where you go from a couple of different families into many, many groups of families, how those kinds of things happen on this planet or on any planet.

Lindsay Hays: And the other really interesting thing about looking at the history of life on Earth is that past Earths are almost entirely different environments. There was a time on this planet where there was almost no oxygen on the surface of the planet. And it was still teeming with life. So what does a planet that has no oxygen, what does that look like? What does the life on that planet look like? And by studying the past Earth and the history of life on Earth, you can get an idea for some other, sort of, states of habitability that we don't see today but that we might be able to see as we're looking to bodies within our solar system, or extra solar planets. Past Earth can be the clue, it can teach us about not just this planet but a lot of other places as well.

Jim Green: Well, let's see, about 3.8 billion years ago we believe life really started here on Earth, and it was really simple for long periods of time. And then it got to be more complex, meaning cells were getting together and forming much more complex structures. What happened that made that change? Do we know?

Lindsay Hays: Well, I mean, one of the things, one of the interesting things about studying the history of life is we can only, sort of, see the winners. We see today how things worked. And so when you look back, when you look back at Earth, and you look back at Earth's history, you could understand, sort of, how we got to where we are. But we don't necessarily know all of the different things that we're acting on that life, all of the different factors.

Lindsay Hays: But one of the things that we always see as a way to, sort of, drive new innovations and drive new evolution is competition, things for resources, place where you can get energy, understandably the places where energy is easy to get and abundant, those are places that life probably started and probably started inhabiting very quickly. And as those areas, those niches filled out, you would expect evolution to become more complex in a way to get our energy that's harder to get at.

Lindsay Hays: So we think about the abundance of life on this planet today that uses sunlight for energy, but that's actually a relatively difficult thing to evolve. It's much more easy to get chemical energy and then the ability, evolving the ability to create what we call photosystems, complexes of proteins and metals and things that allow you to take energy from sunlight, that's just one stage of complexity as you evolve.

Lindsay Hays: The next thing is multi-cellularity. And as you were sort of alluding to, more complex structures, those sort of thing. It's really hard to try and understand exactly what drove those evolutions, but actually there's a recent study that came out that showed that predation, single cells that eat other cells, can actually drive those prey cells to create more complex structures, to become multi-cellularity as a way to sort of protect themselves from predation. Think animals living in herds makes it harder for any one animal to get attacked.

Jim Green: Early on when plants came on this Earth, what kind of plants do you think started here first?

Lindsay Hays: Well, so we're definitely talking, early on, we're talking single-celled organisms. So, cyanobacteria. These used to be called blue-green algae. But as we have understood them better we recognize that they're not algae at all. They're in fact a single-celled organism called cyanobacteria. They live in communities. But you probably know them as chloroplasts. So, at some point in the past couple billion years a different organism ate a cyanobacteria. It became incorporated in the cell. It wasn't digested for some reason or another, and became a chloroplast.

Lindsay Hays: And that's where we start to see algae and all those kinds of things. And then algae evolved into bigger things as life — first water, plants, and things like that. And then plants on land have only been around the past couple hundred million years. So early on, we’re definitely talking about, not even algae, but even single-celled bacteria that are photosynthetic.

Lindsay Hays: With the evolution of photosynthesis, we sort of see two stages. The first stage in the evolution of photosynthesis is just the ability to take in light at all. But then as those photosystems, those complexes became more complicated and started grouping together, a group of organisms that are probably like modern day cyanobacteria, or the ancient historical version of them, evolved the ability to split water. And in the process they started creating oxygen, which fundamentally changed the chemical composition of the atmosphere and sort of the surface environments on Earth.

Lindsay Hays: And the really neat thing about oxygen is that it allows you, it's a really high-energy molecule, and it allows you break down more complex compounds. When you can consume oxygen and sugars, you can, sort of, get the full amount of energy out of those sugars. And that allowed things to become more complex because they can sort of get more energy out of the food they are eating. So, those processes and, sort of, a whole series of evolutionary steps allowed us to take the steps from being, sort of, simple life to this very multiple complex organisms we see today, all of the different kinds of singled-celled through elephants and whales and these huge enormous things that we see on our planet.

Jim Green: Well, you know, can you tell us about some of the places in the solar system that you're excited about for looking for life?

Lindsay Hays: Ooh. Okay. Do I have to stay within the solar system?

Jim Green: No, actually. Beyond Earth, where would you go look for life beyond Earth?

Lindsay Hays: So, of course, there's a lot of interesting things outside of the solar system. Whatever you can imagine, there's probably some really cool planet outside of the solar system that's like that. But I like thinking about our solar system because it's a much more approachable environment. These are places that even in the farthest regions of the solar system ... We've been to Pluto. It took us a long time to get to Pluto, but we've been there and we've been able to do that. So I'd say that there are a lot of places that I find really interesting in the solar system.

Lindsay Hays: And most of them are, sort, of in the sub-surface. Right? Deep under the surface of Mars in the rocks, under the oceans and the moons in the outer solar system. The things that I'm most excited about in our quest to look for life is to understand what makes an environment habitable on a planet or on some other body in the solar system, a moon or something that's potentially less habitable as a whole than the Earth.

Jim Green: Well, you already mentioned a couple of really great places. You mentioned Mars and you mentioned the icy moons. If life is in both of those places, would they be similar or how different would they be, do you think?

Lindsay Hays: You’d have to see different evolution, different systems that would have evolved to live in those different places. When we look at our planet here, extremophiles are very different depending on the environments that you look at. When you look at things that live in deep sea environments, like the kinds of environments that we imagine we would see in some of the subsurface oceans on the moons of the outer planets. We see organisms that are evolved to live in high pressures and high temperatures.

Lindsay Hays: When we see things that live in rocks on the earth, we see things that are evolved to take advantage of tiny little bits of energy over very long lifetimes. Those things on the Earth eat hydrogen and other things like that that come from radioactive decay. But those two organisms have evolved into, sort of, very different types of systems. And so I would imagine that you would expect to see different kinds of lifes if you're looking at different environments.

Jim Green: Well, we know a lot about Mars, and I think we could say there's probably not life on the surface of Mars, at least we haven't found it yet. But that gives us the opportunity to think about life below the surface. Would we rule out life below the surface on Mars?

Lindsay Hays: Would I rule out life on the surface, in the subsurface below Mars? Any time that we look for life, almost any place that we've looked on this planet for life we have found it, which tell me that life is incredibly robust. It stays wherever there is energy to be had. So I think that if there was ever life on Mars, it may be somewhere on the surface today. And I think ruling out life ... I'm an astrobiologist, so I never want to rule out the potential for there to be life somewhere. I think that life is clearly not abundant on the surface of Mars today. And so I think looking in the subsurface is exactly the kind of thing that we should be doing.

Jim Green: But do we know enough about Mars to rule it out, or is it still a possibility that there might be life on Mars below the surface?

Lindsay Hays: I think that there’s, I think that there are enough tantalizing hints that I think it would be interesting to go and look for life in the subsurface. I definitely don't think there's anything that we've been able to rule out with regards to Mars at this point, other than, like you said, the fact that life is clearly not abundant on the surface of Mars today. So where could it be and what would it look like? Those are really interesting questions.

Jim Green: Well, what are some of the signatures of life that we should be looking for, then?

Lindsay Hays: Well, on Mars or anywhere?

[Orionid]

Gravity Assist: Could We Find Billion-Year-Old Cholesterol? With Lindsay Hays (2)


Astrobiologist Lindsay Hays holds Martian meteorite ALH84001. Credits: Lindsay Hays

Jim Green: Yeah. On Mars or any place. Let's start with Mars.

Lindsay Hays: Things like chemical fossils. The simplest things, really, are looking for evidence of disequilibria. I mean, fundamentally life takes advantage of a place where there's energy to be exploited and takes that energy for itself. So something that indicates that there's been some kind of chemical reaction that's going on there. I am a organic chemist, so I always want to look for organic fossils, things like lipids or amino acids, things like that. Micro fossils, you might see traces of single-celled organisms or sometimes those single-celled organisms live in, sort of, communities and create macro-fossils.

Lindsay Hays: On Earth, we see these things as stromatolites where evidence of, sort of, sticky microbial mats that haven't gotten broken up in storms and things like that and redeposited and indicate that there was something there that was doing something.

Lindsay Hays: There's a whole range of biosignatures. And some things, you may be more likely to see them on Mars. Some things, you'd be more likely to see them in the subsurface ocean or in a plume from a subsurface ocean, those kinds of things.

Jim Green: Well, we've been talking about the building blocks of life for a while. And everyone knows about amino acids. But you mentioned one thing, lipids. And so, what are lipids and how would we look for a lipid as a biosignature?

Lindsay Hays: Sure. So, I like to think about lipids in this way, and that is if you are very, very, very lucky, the parts of you that may last for billions of years, that says that you were here, is actually your cholesterol. Lipids are the things that make up our cell membranes. They are the things that sort of make up the envelopes around our cells. And unlike DNA that would say, "This was Jim Green who was here," these lipids are produced by, sort of, whole families of organisms. They can tell you this was a human or this was a mammal who was living here.

Lindsay Hays: But they last a really, really long time. These are basically oils. One reason that we can find oil is that it can be preserved for millions or even billions of years on this planet. And these hydrocarbons, they last for a really, really long time. They can be a really good record of the deep past, and different families make different compounds that allow us to say, "Hey, look. Something that was making that compound lived here at this time in the past." And you can see whole groups of lipids. It's a really great way to understand, sort of, the history of the microbial life on this planet, since they don't always leave fossils in the way that dinosaurs do.

Jim Green: Yeah. That's really fascinating. I mean, you know, and most of history of Earth, animals didn't have a skeletal structure. They were much more cellular in nature. So as you say, we're going to have to find the right pools of chemicals to be able to see that these are markers of ancient life. Well, what kind of instruments or technologies do we really need to develop to be able to make those kind of measurements?

Lindsay Hays: Well, as I said, I'm partial to lipids. They last for really long periods of time. So, I'm always interested in things like the spectrometer.

Jim Green: What is a spectrometer and how would it work?

Lindsay Hays: So there's a couple of different ways. A spectrometer ultimately is something that is looking for wavelengths of light. And so we can think about a spectrometer as a way to look at how different compounds, what different compounds there are in a gas or something like that. We also have things like mass spectrometers which helps us to look at the ranges of mass that we get out of compounds that we have broken down. And these are all things that allow us to, sort of, do an inventory of the chemicals that we are looking at in a place.

Lindsay Hays: You can detect other compounds as well with a spectrometer, like amino acids, like you were talking about. or make atmospheric measurements depending on sort of how you set it up. Some people have argued for a camera as a way. to sort, of detect life. This could be a very hard thing to do.

Lindsay Hays: But if we send a camera, say, to a subsurface ocean, you’d have to do a lot of filtering of sea water to find microbes and stuff like that. And how would you even know what you were looking at? But the stuff that I'm most interested in looking at is in the deep subsurface. So, instruments, we have some idea of what kinds of instruments we may want to create. But really the technologies, I think, that are important are about how to get into that subsurface, how to get below the ice, how to get samples of stuff below of ice, how to get below the rocky surface of Mars.

Lindsay Hays: You have to think about getting sampling systems that are robust. Remember, we have no mechanics in outer space. You have to make sure that it's going to be able to do what it's going to be able to do, and you can't fix it. And also how to keep them very clean. We don't want to run the risk of bringing Earth life with us, detecting it, and saying, "We found life." But really what we found was ourselves. So, I think that those are some really interesting technologies that when we combine them with the instrument development that some of our great teams are doing, can get us to not just being able to measure things but getting the samples that we may want to measure.

Jim Green: It just occurred to me as you were talking about it, getting below the surface, if you go to Mars, there are some really deep craters that really get below the surface. I mean, they can be hundreds of meters below the surface. Maybe that's where we should land and begin our interrogation, because it's down already at a low level.

Lindsay Hays: The rocks can always tell a story. We use the rocks on this planet to tell a story about the deep past. The most interesting thing I think about the history of Mars is that the rocks on the surface of Mars are on the whole even older or significantly older than the rocks on the surface of the Earth. And so, they also tell the history of Mars right there on the surface. And because they've got craters and because they've got other things like that, that's exactly, that’s your window into those deep subsurface rocks.

Lindsay Hays: And a really cool way to look for either these chemical fossils, lipids, those kinds of things I was talking about or microfossils, as long as you can find rocks that, sort of, are sedimentary, they're unaltered. They may have these fossils ... If those fossils exist, those would be the right places to look for them.

Jim Green: Yeah. Now, the one thing about Mars, as you mentioned, is the surface rocks are older. And it's because the rocks here on Earth have gone through a whole evolutionary stage of being modified by plate tectonics and wind

Lindsay Hays: Yeah

Jim Green: And weather and ocean. And so, we don't have any of the old rocks on the surface anymore. It's really, kind of, turned over.

Lindsay Hays: There's a really active question within the habitability community, which is do we need plate tectonics for life to live on the surface and to be abundant on the surface? So, understanding not just local environments for habitability, but global environments for habitability. Plate tectonics are great because they, sort of, keep refreshing your stores of chemical energy. They turn it over and they reprocess it, they repackage it into new pieces that microbes or larger organisms can eat.

Lindsay Hays: But at the same time, they destroy all of those old signals. They destroy all of those old signs. And so it's a two-fold kind of thing. What are you looking for? Are you looking for the rocks and the history of the old life? Or are you looking for something that's active today?

Jim Green: So indeed, if life started on Mars at the same time it did Earth, then the way we could find how life started originally would be on Mars.

Lindsay Hays: Yeah.

Jim Green: What kind of studying and training does someone have to have to become an astrobiologist?

Lindsay Hays: So, astrobiology requires that we think about big questions. And so, to answer big questions, you have to get people who have a lot of different kinds of backgrounds. So, you know, the study and training, you have to be very interested in science. You have to be very interested in engineering, that kind of thing. But really, you've got to be thinking about how to work with other fields.

Lindsay Hays: So, I trained as a geologist and a biologist, but I also took a lot of chemistry classes. I took some classes on planetary science and understanding how planets form and what makes a planet habitable. It’s really… the kind of training that you need is really focused on teaching people to have an open mind. In astrobiology you have to know no matter how good you are in your field, the kind of questions we want to answer are the big questions. And so you're going to need to be able to work with other people to figure those out. So, think lots of science, but also learning how to work with other people.

Jim Green: Well, Lindsay, I always love to ask my guests to tell me about what happened in their past. What person, place, or activity that got them so excited about being a scientist that, I call that a “gravity assist.” So Lindsay, what was your gravity assist?

Lindsay Hays: Ooh. Can I give two. Can I give some rocket going into the outer solar system, needs a couple of swing-bys to get me where I am?

Lindsay Hays: Well, the first thing is sort of a quirk of fate. I actually grew up in a little town called Jupiter, Florida. And Jupiter is cool not just because, of course, it's named after the coolest planet in the solar system, but because it's close enough to Cape Canaveral, to the Kennedy Space Center, that you... When I was growing up, you could see the space shuttle launches. Now, you couldn't see the rocket, of course. You could just see the trails and the lights from the engines. But you could see them.

Lindsay Hays: And so a couple times of year if you knew when to look and you knew where to look, you could see people launching into space on a regular basis. And that was just a really cool thing to grow up in the shadow of. The other thing is I had a fantastic teacher in high school. I was not necessarily a great student in elementary school. And in middle school things started to sort of pique my interest. But my high school biology teacher really, really inspired me to get into science.

Lindsay Hays: She’s an amazing woman, very smart. She actually got her Ph.D. while teaching high school in biology and made the material really fascinating in a way that I hadn't been able to engage with before. And so she's actually now the vice principal of the school that I went to. But without her I probably would have been, I don't know, a certainly actor or writer somewhere, because those are things I was always interested in but was never very good at. So, that was Dr. Raiford at Suncoast High School. I would list her as my second gravity assist.

Jim Green:  Oh, that's fantastic. Teachers are so important to all of us.

Lindsay: Definitely.

Jim Green: And it's all about being receptive at the time that they're teaching us. So I'm delighted that occurred for you. Well, Lindsay, thanks so much. It was really a joy talking to you about looking for life and your perspective on finding it out there.

Lindsay Hays: Sure. Thanks so much for having me, Jim.

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

Source: https://www.nasa.gov/mediacast/gravity-assist-could-we-find-billion-year-old-cholesterol-with-lindsay-hays