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Gravity Assist Podcast: Where's the Water on the Moon? With Jen Heldmann (1)
May 30, 2019

The Moon has a large supply of water that could be useful in future human exploration, says NASA scientist Jennifer Heldmann.


The image shows the distribution of surface ice at the Moon’s south pole (left) and north pole (right), detected by NASA’s Moon Mineralogy Mapper instrument. Blue represents the ice locations, plotted over an image of the lunar surface, where the gray scale corresponds to surface temperature (darker representing colder areas and lighter shades indicating warmer zones). The ice is concentrated at the darkest and coldest locations, in the shadows of craters. This is the first time scientists have directly observed definitive evidence of water ice on the Moon’s surface. Credits: NASA

Jim Green: Did you know that there’s water on the Moon? Who would have thought? In fact it’s turning out that the solar system is a soggy place.

Hi, I’m Jim Green, chief scientist at NASA, and this is "Gravity Assist." This season is all about the Moon.

I'm here with Dr. Jennifer Heldmann, a fantastic planetary research scientist working at Ames Research Center in Mountain View, California. And today, we're going to talk about volatiles on the Moon. Welcome, Jen.

Jen Heldmann: Thank you so much, Jim. It's great to be here.



Jennifer Heldmann, an expert on volatiles on the moon, chats with Jim Green, NASA’s chief scientist.
Credits: NASA/Elizabeth Landau


Jim Green: You know, for a number of years now, you've been really doing a lot of research about the Moon, and particularly about volatiles. Well, what does that mean? What are volatiles?

Jen Heldmann: "Volatiles" is just a fancy science term meaning, basically, ices. So, volatiles are things that are very cold and so they can stay as a solid like an ice, like water is one of the volatiles we think of that's most common. We have volatiles in our freezer, right? And then, when they warm up, they can sublimate or vaporize and go away. So, volatiles are very special, because we have to go to the places on the Moon that are very cold in order to find these volatiles. And that's been the trick.

Jim Green: You know, what we're finding out from our estimates is that there's between 100 to 200 million tons of water on the Moon. And actually, that might be an underestimate. So, is water, water everywhere in the solar system?

Jen Heldmann: Yes. That's one of the interesting things. Water on the Moon is same as water on Earth, is the same as water on Mars. Water's water all over the place.

Jim Green:  I would love to get a bottle of water from the Moon. So, Jen, we go to the Moon, and we grab this material and get this rock, how do we get the water out of it?

Jen Heldmann: Right. This is one of the reasons we need samples, so we know what it's like. To first order, you heat it up. That's how we get ice, turn it into water. So you can heat it up and melt it. You can heat it up and vaporize it, like, into steam, because you just want to extract that water out of that rock and whatever else is in there.

Jim Green: So, why is the Moon so special to you?

Jen Heldmann: Yeah, so, the Moon is special for many reasons for me, and hopefully for others as well. First of all, it's right there. Right? You can look up in the night sky, sometimes even in the daytime, and you can see the Moon. It's our closest celestial neighbor. And the Moon actually records a history of our solar system that we just can't get anywhere else. Right.

Jim Green: Yeah.

Jen Heldmann: The Earth is fantastic, but Earth is very dynamic, which is exciting for us. It's changing. Earth has geology and volcanoes and subduction zones and oceans and erosion and weather and all these things that change the rocks on Earth. The Moon doesn't really have all of that activity going on, and so there's a record on the Moon of the early history of the solar system. So you can go to the Moon, and we have records and rocks of what happened when our solar system was first forming, four and a half billion years ago, which is incredible.

And that also translates to the volatiles too, because we had volatiles that were being delivered to the inner solar system, to the Earth and the Moon. And so that record is also preserved on the Moon. So, we go to the Moon, we can understand: What was delivered? How did the water come to Earth? How did it come to the Moon? And we have that record that we can go and look at on the Moon.

Jim Green: Yeah. When you say the volatiles are being delivered, what you're really talking about is stuff like comets and meteorites and things coming out of the asteroid belt that actually have a fair amount of water in them, and then coming inward and impacting the Earth and the Moon.

Jen Heldmann: Exactly, exactly. We're in the same sort of neighborhood in our solar system, so all of those comets and meteorites that were hitting the Moon, probably hitting the Earth too.

Jim Green: Well, the most fantastic discovery in my opinion about the Moon most recently is that it harbors maybe an enormous amount of water. How did that happen? How did we discover that?

Jen Heldmann: Right. So, this has been really rewriting the textbooks over the past decade or so, because even when I was in school, you learned that the Moon is bone dry. There's no water on the Moon. It's just dry rocks, and that's--

Jim Green: Now, how did we get to that point?

Jen Heldmann: Well, we have some samples from the Moon. We have from the Apollo astronauts, who went to the surface of the Moon and brought rocks back, mostly from areas near the Moon's equator, and brought back these rocks. And we have them in labs here on Earth with very fancy, sophisticated lab instrumentation. And those rocks are pretty dry.

Jim Green: Yeah.

Jen Heldmann: So, not much water there.

Jim Green: Right. So that's how it started. To us, today here on Earth, it's like if you landed in the desert and you claimed the rest of the Earth is that way, well, that's what we did.

Jen Heldmann: Right. Exactly. It's we got, we got,

Jim Green: We got it wrong.

Jen Heldmann: But then we sent a few more missions to the Moon, and we started getting a little bit smarter and learning a little bit more. And we realized that near the poles of the Moon, there are these very special regions that are in permanent shadow. And, they're at the bottoms, usually, of craters, or depressions. And the Sun has not shone there for sometimes billions of years. It's very cold, just because the tilt of the Moon, the way the Sun's angle comes in.

Jim Green: Yeah. First it was all about, from the Lunar Reconnaissance Orbiter, seeing these areas that never get Sunlight. And then, measuring their temperatures remotely from one of our instruments, and that's when we see that these permanently shadowed areas are some of the coldest in the solar system.

Jen Heldmann: Right. Exactly. Some of them are colder than Pluto even, super cold.

Jim Green: That's got to be cold. That has really got to be cold. All right. Well then how did we figure out there was water in those places?

Jen Heldmann: Yeah. So, we got the Lunar Reconnaissance Orbiter data, and we saw that there are these depressions. And we saw the temperatures were really cold. And then we got some interesting data from neutron spectrometers. So, that's just a fancy science measurement for looking for hydrogen. And we saw these enhanced levels of hydrogen near the poles of the Moon near these permanent shadows. And, of course, where we see hydrogen in these areas, what's water made of? H2O, hydrogen and oxygen.

So, then we started thinking, "Wait a minute. So, is this hydrogen water ice?" And so NASA decided to send another mission to say, "Okay. The goal is to touch that ice. We want you to go there, and we want you to go down in one of those permanently shadowed regions where you see lots of hydrogen, where the Lunar Reconnaissance Orbiter says it's really cold and really dark, and tell us if there's ice there."

Jim Green: So the concept then is, okay, we're going to touch that ice. And the first thing that comes to my mind is, okay, we're going to build a rover, and then that rover is going to land, and then it's going to go down these steep hills and go into a crater and touch it. And now it's becoming really more complicated, because it ends up running into that permanently shadowed region. Where is it going to get its power? But a new idea came out on how to touch that ice. What was that idea?

Jen Heldmann: Right, exactly. For just those engineering challenges that you mentioned, it's really hard to drive a rover in the dark. And it's really hard to keep electronics on a rover working at very, very cold temperatures. And it's very hard to get that data back. So, we had to go back and think. All right. How can we do this? And so we came up with this idea of an impactor. We thought, "You know what? If we can send something in there to hit the bottom of that crater, and then kick all of that dust and debris, ice if it's there, kick it up above the lunar surface where, then, we can see it in the Sunlight, then maybe we can tell if there's ice there."

Jim Green: Yeah. When it gets in the Sunlight, then it has its own fingerprint. Then you have the absorption and readmission of light from the Sun. And that fingerprint tells us what it is. So, so the hope was not only water, but maybe other kinds of volatiles that we can measure, too.

Jen Heldmann: Exactly. And so we did that. And we did that with NASA's LCROSS mission, the Lunar Crater Observation and Sensing Satellite.

Jim Green: LCROSS.

Jen Heldmann: Yes, clever acronym.

Jim Green: Clever acronym.

Jen Heldmann: As all good NASA missions have.      The Lunar Reconnaissance Orbiter, or LRO, was launched in 2009.

Jim Green: And with LRO was LCROSS. So, what happened next? Did we get them both into orbit, or how did that work? 

Jen Heldmann: Right. So um, LRO was the primary mission, and LCROSS was sort of stacked on top of it on the launch vehicle, on the rocket. And they both launched from Florida together towards the Moon. And then they separated shortly after that because LRO, of course, went into orbit around the Moon. Still in orbit around the Moon. Still collecting great data, sending that back to Earth. And LCROSS went and had a little shepherding satellite on it. And it had all the science instruments, and it dragged along the upper stage of that launch vehicle, that rocket. So, basically, on the way to the Moon, we emptied out all the fuel, so now we have a big, empty metal can, which used to be the upper part of the rocket. We baked it out in the Sun, make sure it's clean, make sure there's nothing in it. And then that shepherding spacecraft basically tugged it to the Moon and got it on the right trajectory.

We said, "Okay. Now we're going to hit in the bottom of Cabeus Crater at the lunar south pole," very cold, very dark hole near the lunar south pole. And the shepherding spacecraft separated from that upper stage. The upper stage went in first, hit the floor of Cabeus crater, kicked up a big plume of dust, debris, and all sorts of other junk and ices that were in there, and then the little shepherding spacecraft, with its nine science instruments, actually flew down, flew through that plume, collected data, collected those spectral fingerprints, those signatures of the ices that were in there. And then that shepherding spacecraft, four minutes later, it also impacted the Moon in Cabeus crater.

Jim Green: Yeah, you couldn't save it, but that's the job it was sent to do.

Jen Heldmann: That's right. That was the plan, those four very important minutes of data.

Jim Green: Wow. So, what did we learn from it? What did we get?

Jen Heldmann: So, what we learned is that there was more water ice there than we even thought. There was about 5% to 6% by weight water ice.

Jim Green: Wow.

Jen Heldmann: Which is a lot. That's more than you can find in water in some deserts on Earth. So, that was answering the number one question: Is there water ice in these permanently shadowed craters? The answer for Cabeus was definitely yes. But then we also found a lot of other things too, found lots of other ices like methane ice and other, C2H6 and all sorts of different compounds.

Jim Green: More complex compounds, huh?

Jen Heldmann: Yes, more complex ices. And it turns out that the signatures of those ices, very similar to what you see in, for example, comets. And so that brings up a nice science question of: Where did those ices come from? And it probably goes back to our story we were talking about earlier about delivery from comets and asteroids of these materials into the inner solar system when the Earth and the Moon system and other planets as well, were hit by these comets and meteorites, and they're bringing in all these volatiles and ices. So there's an interesting story scientifically being teased out.

Jim Green: Yeah. There really is. So, it's still hotly debated, but the concept after the Earth formed and the Earth Moon formed from an impact of a Mars size object. Once that occurred, and both these objects were so hot, they must've been releasing all kinds of volatiles and releasing all kinds of water. So then the Earth lost a lot of it. How did it get it back? Where did the oceans come from? And of course, having comets and meteorites bring that water back to the Earth has been one of the top theories. And it ranges, depending on what scientists you talk to, that it maybe 20%, or maybe 50%, 60-or-more percent of the water here on Earth came from these kind of impactors. That's really fantastic. Now that we know the water's there what other kind of missions are we planning to do? Because we really have to figure out how much is there.

Jen Heldmann: Right. Exactly.  We answered: Is there water ice in these permanently shadowed regions on the Moon? The answer to that is yes. So then, then the next question becomes: Okay. Can we use that water? Because one of NASA's goals is to send humans forward to the Moon. Right? We want to send people to the Moon to stay for longer periods of time, and have a more sustained human presence on the Moon. And one good way to do that is to use resources that are already on the Moon. And if you can use the water that's on the Moon, that is a great resource that will greatly enhance our ability to send people.

Jim Green: To me, that is the game changer. I mean, the concept that we actually have a ready supply of H2O. You can bust it apart. You've got oxygen to breathe. You've got the H and the O that you can use for rocket fuel. And you can still use it as water to drink, so I mean it's just such a game changer. Our thoughts now are indeed, as we go forward to the Moon, we'll indeed interrogate first the south pole region, where there's that water.

So, how are we going to do that? What's next for the exploration of the Moon in this area?

Jen Heldmann: So, We're looking at: How can we best utilize this ice resource? And how can we access it? ‘Cause, as we talked about earlier, if you want to go to the bottom of a deep, dark, cold crater, that's pretty tough from an engineering perspective. So, we've gotten smarter, and with some data from the Lunar Reconnaissance Orbiter, some of the temperature data, and then some of the elevation data for modeling temperatures and thermal regimes, we figured out, and also with the neutron data, that there's probably water ice. You don't have to go into the permanently shadowed regions.

But there are places near the south pole of the Moon, lots of areas, that get, you know, seven to 10-ish days of Sunlight per month. And so if you go down a few centimeters, a few tens of centimeters down below the surface, you're at those same cold, cold temperatures where those volatiles, or those ices, are stable.

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Gravity Assist Podcast: Where's the Water on the Moon? With Jen Heldmann (2)


Jennifer Heldmann attended Space Camp in her youth, and now she works at NASA’s Ames Research Center. She is pictured with Jim Green, NASA’s chief scientist. Credits: NASA/Elizabeth Landau

Jim Green: Yeah, so they're trapped a little just below the soil there, the regolith. Maybe those things had hit, other impacts occurred, and laid material on top of it, and that's what's protected it.

Jen Heldmann: Right. So, if we can use that ice that's in these areas where you can actually work and operate in Sunlight, that would make our lives a lot easier. So, the next thing that we need to do is really get on the surface of the Moon and ground-truth that ice. Where is it? How deep is it? Is it mixed with other ices? How much regolith do you have to drill through in order to get to it? Answer all of these fundamental questions that are so important for designing the engineering of the hardware that you would have to bring.

Jim Green: Well, one of the things that I think you're doing a fantastic job in, is field work. Tell me a little bit about practicing things that we would do on the Moon by doing that here on Earth.

Jen Heldmann: Right. That's one of the nice ways that we can prepare for these types of missions, is to use what we call terrestrial analogs. So, these are places that are on Earth that have characteristics that are similar to the Moon. For example, for doing testing for, say, a rover mission, to go and try and ground-truth this ice that's in these sometimes-Sunlit regions near the Moon, it's a very different way of doing rovers than we're used to. For example, for Mars. Mars is very far away. There's a long time delay. You uplink your signals one day. It gets sent. The rover does it. Then the next day, you hear back from the rover and it tells you what it did.

The Moon is much closer. Right? We can be in almost real-time talking to rovers on the Moon. For example, one thing we did is: we took rovers with prospecting instrumentation, so a near-infrared spectrometer and a neutron spectrometer, which can measure those fingerprints, those signatures of the ice. And we took that and mounted it on a rover and took that out to the Mojave Desert in California, which has about the same, by weight, water percent that we're seeing on the Moon, so very dry area, but still enough water that you could see the signatures in the instruments. And so we ran that mission just like we would run the mission on the Moon. Right?

We did not let the scientists go out into the field. Scientists always want to go to the field site. But they're not allowed, because when we do it on the Moon, all the scientists will not be walking on the Moon. You'll be in a back room or a science room on Earth.

Jim Green: In a control room.

Jen Heldmann: Exactly. And so you have to be reliant on that data that's coming back from that rover. And so that really makes you work hard to make sure that you're getting the right data, the right instruments, the right information sent back to you. So we sent the rover out into the desert. We remotely controlled it from NASA Ames. We had the data coming back in real-time. And we were able to react to that data in real-time.

For example, if you're driving your rover, and all of a sudden you run over a hot spot, and you say, "Oh, there's a big signature of ice. We should stop here. We should drill here." So you have an all stop. The rover stops right away. It drills. It collects more samples, whatever you need it to do. And then you can command the rover: Okay, keep moving on and go in our pattern.

Or sometimes if you're on the ground, and you say, "Oh, that area over there looks more interesting. I didn't realize that was a good spot. Let's go there," you can change where that rover goes. That's a very different concept of operations, and so we're testing out not only the hardware, the instrumentation, the ability to detect the ice, but also the operations, how you operate it. Who gets to see what data in real-time? What is the chain of command for making decisions in real-time to change what your rover is doing? What are the communication protocols and infrastructures that you need?

All those types of things that get layered onto a mission, you're really integrating the science and the technology and the operations. And by doing this, on Earth, we're just out in the desert on Earth, it's a low cost, low risk environment. But we can really learn a lot about how to make these missions work the best when we send them to the Moon, or to Mars, or to other planets.

Jim Green: Yeah. So that next step, indeed, is to do that our robots on the Moon, and have our astronauts up in the Gateway doing telerobotics. The Gateway, which is an orbiting spacecraft that will house astronauts, is really a unique and important first step going to the Moon.

Just exactly modeling that communication capability between humans in the control center and the robots out in the field. And so indeed, that's just a fantastic way to get ready for what I think is going to be an unbelievable decade of exploration at the Moon. And that will lead then to how we will explore Mars.

Jen Heldmann: Right. Exactly. This is all feed forward to Mars, because of course, Mars also has water ice.

Jim Green: Right.

Jen Heldmann: --in its subsurface.

Jim Green: Correct.

Jen Heldmann: And it's thin atmosphere, and so we can test all of these prospecting techniques, the ability to extract the water ice, to test it, to purify it, and to use it. And we can test this all on the Moon before moving further away and going out to Mars, which is of course, a longer distance, more time delay. The astronauts and hardware have to be more self-reliant, as opposed to being on the Moon. The Moon is a great testing ground for then future applications to Mars.

Jim Green: You know, NASA's planning to send astronauts and have the first woman to step foot on the south pole of the Moon by 2024. Jen, that could be you.

Jen Heldmann: It could be, but there's probably some folks in the astronaut corps that can do that.

Jim Green: Well, this is why, as you say, the field work is so important.

Well, you know, Jen, I always ask all my guests to tell me a little bit about what happened in their life, what person, place, or thing, or event, that got them so excited about planetary science, that they decided to become the scientist they are today. I call that a gravity assist. So Jen, what was your gravity assist?

Jen Heldmann: Am I allowed to have two?

Jim Green: Yes, of course.

Jen Heldmann: Okay. I think first gravity assist was in about third grade.

Jim Green: Wow.

Jen Heldmann: Yep. And for some unknown reason, we had a small telescope in our basement. And for some unknown reason, one night my mom pulled it out on the deck in our backyard in central New York. And we pointed it at the Moon. And my goodness, if you look through a telescope, even a small one, at the Moon, it's a real place.

Jim Green: Yeah!

Jen Heldmann: There are mountains. You can see the ground. You can tell that it's made up of rocks. And for the first time, I realized that the Moon was another world. It was a place where you could go. You could walk there. It was a real thing. So that was the first sort of real gravity assist that made me realize, wait, there's something out there beyond. It's not just this bright ball in the sky.

Jim Green: And the Moon started it.

Jen Heldmann: It's a place, yep. And then I think the second gravity assist came a little later in about high school when I discovered there was this place in Huntsville, Alabama, and it was called Space Camp.

Jim Green: Yeah.

Jen Heldman: At the US Space and Rocket Center.

Jim Green: Right.

Jen Heldmann: And I did a lot of chores, and I worked some odd jobs, and somehow I got myself to Space Camp.

Jim Green: Wow.

Jen Heldmann: My first flight on an airplane, it was a big deal. And there were people like me who really loved space. And it was the first time I was surrounded by people who thought about this as a job. Like, you could do this as a job. I didn't know that.

Jim Green: How cool is that?

Jen Heldmann: I had no idea. I didn't realize that. And so that was a game changer, I think, because I realized: Wow, I could study this in school, and I could go do this one day.

Jim Green: And you did.

Jen Heldmann: So far.

Jim Green: Yeah, you're doing great. And I can see that progression, of course. Space Camp provides you a really good connection on human exploration, and your interest to going to the Moon and that naturally leads you to doing the fieldwork that you're doing today, which is spectacular.

Jen Heldmann: Thanks. Yeah, it's fun.

Jim Green: So, Jen, it's just been a delight to have you here. I really appreciate the opportunity to come and talk about volatiles on the Moon.

Jen Heldmann: Thank you so much, Jim. I really appreciate it.

Jim Green: Well, join me next time as we continue our exploration of the Moon. I'm Jim Green, and this is your "Gravity Assist."


Lead Producer: Elizabeth Landau

Audio Engineer: Emanuel Cooper


Source: https://www.nasa.gov/mediacast/gravity-assist-podcast-wheres-the-water-on-the-moon-with-jen-heldmann