August 26, 2022
When you think of ice, you might imagine glaciers, the North Pole, a clink in your water glass. But it turns out that our closest neighbor in space isn’t just a dusty ball—the moon has ice tucked away in deep craters at each of its poles. On top of that, scientists think the moon stole its ice: from comets, asteroids, maybe even from the Earth. We talked with two scientists—Kathleen Mandt and Nicholas Hasson—who are studying how the moon snagged its ice and how astronauts might use that ice on future missions.
Shane Hanlon: 00:00 Hi, Vicky.
Vicky Thompson: 00:00 Hi, Shane.
Shane Hanlon: 00:02 Prompt for you today might be a… You can choose to answer this or not, have you ever stolen anything?
Vicky Thompson: 00:09 Oh my gosh.
Shane Hanlon: 00:12 I know, I know, I don’t want you to self-incriminate-
Vicky Thompson: 00:14 What a hard question to ask on a recording device.
Shane Hanlon: 00:18 I know, on a podcast that goes out to many people.
Vicky Thompson: 00:21 I’m more of a light vandalism kind of person.
Shane Hanlon: 00:24 Okay.
Vicky Thompson: 00:24 Yeah.
Shane Hanlon: 00:25 All right.
Vicky Thompson: 00:27 I enjoy looking at the the, “Slap Stickers,” as the kids are-
Shane Hanlon: 00:27 Oh, I see-
Vicky Thompson: 00:33 Are calling them. Yeah.
Shane Hanlon: 00:34 Sure.
Vicky Thompson: 00:35 But stolen anything, no, the only thing that I have in my possession that is stolen was stolen by my daughter, my daughter’s a little thief. Yeah.
Shane Hanlon: 00:48 What? How old is your daughter? Remind me.
Vicky Thompson: 00:55 She is almost five.
Shane Hanlon: 00:57 Okay.
Vicky Thompson: 00:57 Yeah.
Shane Hanlon: 00:58 So, what’s the deal here?
Vicky Thompson: 00:59 So years ago, so pre-COVID, I think she might have been three, so our good friend, Nancy, right?
Shane Hanlon: 01:06 Oh, yeah, Nancy.
Vicky Thompson: 01:07 Yeah. Nancy who we know and love, we were over visiting her and her partner at her house, and we had a grand day of dancing, and we had many injuries, many toddler injuries at Nancy’s house, anyway, we had a great fun day, and then when we got home, I was unpacking Olivia’s things and there was a small, sparkly lava lamp nightlight in Olivia’s things, so I’m not sure how she obtained it, but she obtained it from Nancy’s house, and now it’s ours. Yeah, that’s my stealing things, yeah.
Shane Hanlon: 01:48 Oh, that’s amazing. I love that you still have it. Do you plug it in? Do you use it?
Vicky Thompson: 01:54 Yeah. Yeah. Except I’m like a Nervous Nellie about electrical things.
Shane Hanlon: 02:00 Oh, I see.
Vicky Thompson: 02:01 So we only plug it in sometimes, it’s a special treat.
Shane Hanlon: 02:04 No, that’s still nice, a thing you can treasure forever.
Vicky Thompson: 02:07 I can treasure, yeah, a little piece of Nancy at my house all the time. Well, what about you?
Shane Hanlon: 02:16 No, I don’t want to talk about it.
Science is fascinating, but don’t just take my word for it, join us as we hear stories from scientists or everyone, I’m Shane Hanlon.
Vicky Thompson: 02:16 And I’m Vicky Thompson.
Shane Hanlon: 02:36 And this is Third Pod From the Sun. Apparently your daughter, Vicky, isn’t the only one who enjoys stealing things, bless her little heart, today we are talking about an unexpected thief, the moon. So producer, Sara Whitlock is here to talk us through an outer space, space heist, outer space heist, outer space, space, heist, I like that better, anyways, hi, Sara.
Sara Whitlock: 03:11 Hey, Shane.
Vicky Thompson: 03:13 Wait, what could the moon possibly steal?
Sara Whitlock: 03:15 So that’s where things get a little bit surprising. Most of us probably imagine the moon as a big dusty ball and that’s not totally wrong, it’s actually hiding water though, water that’s been frozen into ice if you know where to look for that water, and ice water came from somewhere else, it didn’t start off on the moon.
Vicky Thompson: 03:31 So it stole its water?
Sara Whitlock: 03:33 That’s right. But the big mystery is how it happened. Scientists have a couple ideas about the way the moon snatched its ice water and today we’re talking to two scientists, Kathleen Mandt and Nicholas Hasson, who each came up with ideas about how this heist happened, that they both published this year.
Shane Hanlon: 03:47 I love this idea of the moon as an extraterrestrial thief, sneaking water past everyone. All right, let’s get into it.
Kathleen Mandt: 03:57 I’m Kathy Mandt, I’m a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
Nicholas Hasson: 04:06 My name is Nicholas Hasson, I’m a Geoscientist at the University of Alaska, currently working on my PhD in studying the cryosphere in earth’s polar region.
Sara Whitlock: 04:19 So can you give me a little bit of background about how people first learned that there was ice on the moon?
Kathleen Mandt: 04:24 Yeah, the theory that ice could exist on the moon first came about when we started studying the geography or the topography of the moon, and we observed that there were regions on the poles of the moons that never experienced any sunlight, so they were permanently cold, they were permanently in shadow.
And when we realized that these conditions existed in the poles of the moon, we started to theorize about what could be stable there, because if you look at the regions of the moon that experienced sunlight end up heating up to such temperatures that water is not going to be stable on the surface at all, but in these regions, the temperatures are cold enough that water could be stable on time scales of millions of years.
Nicholas Hasson: 05:13 Actually, I believe the coldest recorded temperature in our solar system, as we know, as measured, are inside of these lunar craters, something like near absolute zero in Kelvin, and so, recent experiments have actually sent things into the craters causing the craters to sort of explode and send out material, and that’s how partly we know that there’s signatures of water ice, perhaps as clathrates which form in these extreme temperatures, right?
Sara Whitlock: 05:49 So yeah, that would be a good moment to maybe take a step back and give us an overview of the different ways that people think water might have gotten on the moon.
Nicholas Hasson: 05:57 Basically, there’s kind of these five major hypotheses, and the first one, the sort of foundational evidence is that the moon formed from a giant collision with a planetesimal called, “Theia,” so this was like a Mars-sized planet that hit earth about four and a half billion years ago, and so that would’ve formed a giant ring of debris around earth, so earth would’ve had a big ring like Saturn and that condensed into the moon, and all of that kinetic energy that’s balled up into the moon would’ve allowed a very active geological process for example, volcanism.
Kathleen Mandt: 06:37 And that was back in the ancient history of the moon, the moon was much more volcanically active and there was lava flowing on the surface and lava gases being released into the atmosphere of the moon. Right now, the moon doesn’t have an atmosphere, so to say, we call it an, “Exosphere,” because there are a few molecules that are surrounding the moon and there’s a cycle of the atmosphere or the exosphere.
But when volcanic outgassing was present, there’s theories that the atmosphere of the moon could have become pretty thick and collisional and full of lots of gases, so that could have potentially delivered very ancient volatiles to the permanently shaded regions of the moon.
Sara Whitlock: 07:25 Just to make sure I’m understanding you correctly, can you talk a little bit about what a volatile is?
Kathleen Mandt: 07:29 Yeah. A volatile is a molecule that is generally in gassiest form on the earth surface, so things like methane, is a volatile, but also water is also considered a volatile as well, that’s not a very good definition on earth’s surface.
Sara Whitlock: 07:49 So even though water is usually, we find it in a liquid form, it’s considered volatile?
Kathleen Mandt: 07:54 Yeah.
Nicholas Hasson: 07:56 The other leading sort of foundational thing is what do you observe when you see the moon? You see all these craters. So we know that asteroids or chondrites have been slamming into the moon, particularly during the late heavy bombardment and that comets would’ve deposited water, and asteroids would’ve deposited water, but still this is process that maybe happened a billion or two billion years ago.
Kathleen Mandt: 08:22 And then there’s also micrometeoroids, which are these small rocks throughout the solar system, and they’re constantly impacting the surface of the moon on a regular basis. We don’t have the problem of those impacting the surface of the earth because they’re so small that they would burn up in our atmosphere, but the surface of the moon is subjected to these impacts on an ongoing basis of micrometeoroids.
So those are the three types of impactors that can be a source of water and other volatiles for the moon. And then the final one is from the sun itself, the sun is constantly sending out a flow of ions and electrons into the solar system, and this flow is traveling at billions of miles per hour, and it’s called, “The solar wind,” and the primary ion in the solar wind is hydrogen, or it’s just basically a proton, and when the hydrogen or the protons impact the surface of the moon, it can combine with oxygen that’s in the soil or the regolith on the surface of the moon and form OH and then later combine with another hydrogen to form H20 or water, so that is an ongoing source of water on the moon that is happening all the time.
Sara Whitlock: 09:42 That’s a lot of different sources, it sounds like volcanoes, three different types of things hitting the moon and solar wind.
Vicky Thompson: 09:58 So how will scientists figure out which of these different sources were how ice got to the moon?
Sara Whitlock: 10:04 Experiments to pinpoint the source of the moon ice are actually already happening. Kathleen published a paper this year with new evidence about which way the moon snatched its ice, her paper is based on a NASA experiment where they actually crashed a rocket from a ship called, “The Lunar Crater Observation and Sensing Satellite,” which goes by LCROSS for short, and they crashed this into the moon and then studied dust from the impact.
Kathleen Mandt: 10:24 Yeah. So the LCROSS spacecraft launched with the Lunar Reconnaissance Orbiter, and so, these two missions went to the moon together and LRO started orbiting the moon, and then the upper stage of the Centaur rocket, it was complete, it had all of the fuels had been used, so the fuel wasn’t remaining in there, but they crashed it into intentionally this specific permanently shaded region because the conditions are super cold, so we expected that to be the richest for one of the richest locations, for searching for volatiles. And when it impacted, there was a shepherding spacecraft that followed behind it, and that shepherding spacecraft took measurements in the infrared invisible of the volatiles that were coming off of the surface with time, as it went in and then crashed behind the Centaur rocket. At the same time, the Lunar Reconnaissance Orbiter was orbiting the moon and came back into view and was able to watch the plume as it expanded and make measurements of the plume as well.
Sara Whitlock: 11:37 That sounds like a lot of timing to get lined up.
Kathleen Mandt: 11:40 A lot of crazy orbital dynamics and timing, yes.
Sara Whitlock: 11:44 And so, this rocket was kind of at the end of its lifespan, it sounds like there wasn’t any fuel left.
Kathleen Mandt: 11:49 Yeah. It was intentionally emptied for that because if it had any fuel left in it, we would be concerned that what we were seeing was something we brought with us, so it was important that when we crashed it into the moon, it was empty, and then we tried to take into account any composition of the rocket itself, that it was contributed to the plume, so that was taken into account when determining the composition of the volatiles on the moon.
Sara Whitlock: 12:14 Okay. And what did those different species tell you about where that water ice on the moon might have come from?
Kathleen Mandt: 12:21 Yeah, so what we found was a lot of water and in addition to water, we saw ammonia and carbon monoxide, carbon dioxide, methane, and sulfur bearing species. Sulfur dioxide, and hydrogen sulfide. And each of these species was very interesting because they could be indicators of the source of the water itself because whenever water is delivered, it’s delivered with other stuff. And it could also be an indication of processes that have been occurring on the moon and in that permanently shaded region.
Sara Whitlock: 12:58 Okay. And what did those different species tell you about where that water ice on the moon might have come from?
Kathleen Mandt: 13:05 Yeah. So what we found when we did our analysis of the composition was we focused not on the individual molecules, like sulfur dioxide or ammonia. We focused on the elements that made up those molecules because when water is delivered to the moon, there are processes that can change the molecules into different molecules, like chemistry on the grain surfaces, and then there could be molecules that are lost in the atmosphere, so we couldn’t just use the molecules, we went down to the elements themselves.
And then what we did was we took the ratio of different elements relative to carbon and compared those to the sources and the processes that could cause the ratio to change. What was the two ratios of elements that was really important for us was the amount of nitrogen relative to carbon, and then the amount of sulfur relative to carbon. And this is important because we wanted to differentiate between volatiles that were delivered by volcanoes in the ancient history of the moon, where volcanic activity was releasing so much gas that it could be trapped in these permanently shaded regions and stored for millions to billions of years, or if it was delivered by the impact of either comets or asteroids onto the surface of the moon, and then trapped in these cold traps of the moon.
And we found that in general, a volcanic source was impossible to include, even in mixtures with other sources, and the reason is because volcanoes have a lot of sulfur and a lot of carbon, but very little nitrogen, and we took the most extreme values in nitrogen we could for any possible volcanic source and could not have any contribution from volcanic gas and have the amount of nitrogen that was observed to be present in the plume relative to carbon and relative to sulfur. So the composition of volcanic gas and the composition of the plume were basically incompatible, and we were able to rule out that source.
Sara Whitlock: 15:31 Wow, that seems really exciting, because that means that the water ice had to come from outside of the moon itself.
Shane Hanlon: 15:45 So it’s looking more and more like the moon stole its ice from somewhere else, it didn’t come from the volcanoes that used to be on the moon.
Sara Whitlock: 15:53 That’s right, and it’s still a little unclear how all of the ice got to the moon or if there actually a couple different ways that the moon snatched ice. But Nick Hasson published his own paper this year with a new idea about ice, his group actually thinks that the moon is stealing its water from the earth’s atmosphere as the moon passes through part of the earth’s magnetic field for a couple days in every lunar cycle.
Nicholas Hasson: 16:14 When the moon moves behind earth, it’s engulfed by earth’s magnetotail, so in textbooks you typically see earth is like a giant magnet, you have these field lines, it creates this magnetic bubble, but in reality, the entire magnetosphere is like a teardrop shape or like a tadpole and the tail, the magnetotail or the plasma tail is behind earth, and it’s always there because the solar winds are forming the shape of this magnetotail.
Well, now, imagine the moon as a half crescent and then a full moon, the moon becomes engulfed in this ion shower of earth magnetic fields, but what it’s actually doing is it’s disturbing these field lines and can cause them to reconnect, which diverts the ions from earth back to earth and this is measured. But some portion of the ions are missing, and one hypothesis is that the ions from earth are actually depositing on the moon.
And there’s evidence for this in… As we’ll talk about, there’s evidence of nitrogen and noble gases in the lunar regolith that form an enigma, these don’t seem to come from the early formation or comments, perhaps they’re coming from the solar winds, and so, there’s a way to differentiate what kind of ions are ending up on the moon either if they’re from earth or from the sun.
And so, the recent measurements, really, since 2017… So this is quite new, show that significant a number of earth ions, or terrestrial ions are actually interacting with the lunar environment when the moon is behind earth in the magnetotail or the plasma tail, and so this provided the necessary evidence for us to examine the hypothesis that maybe some of these gravitational anomalies that sure look like water phase have been deposited from earth itself.
Sara Whitlock: 18:24 Okay. So just to make sure I’m understanding correctly, it sounds like the moon is moving through the tail of the earth’s atmosphere when it’s behind, and as it’s doing that because of the way the magnetic field works, ions, so pieces that will become water are raining down on the poles of the moon, is that correct?
Nicholas Hasson: 18:42 That’s correct. And what’s nice is we can test this hypothesis, isotopes from the ice samples returned by the NASA astronauts will tell us the origins and depositional pathways, say, from more recent earth atmospheric escape or long ago by say comets or asteroids or by vulcanism.
And I know they’re going to be doing a lot of this return mission to the moon, the Artemis plan is really focused on geological and geochemistry and active processes and ancient processes, so this is really we’re going back to the moon as an open laboratory, whereas before it was a little bit of nations competing, now we’re going back to really do fundamental science, and so, I would like to see known deposits of ice or water phase that are actually extracted from the surface and subsurface returned, and they’ve even built a fancy new laboratory to look at these isotopic signatures.
So yeah, I’m really interested in the geochemistry there. And so you can use nitrogen and carbon and different isotopes that are really like fingerprints of how these ice deposits formed, and all of that, it’s not like we’re going to maybe know one day, it’s actually, I think by the end of the decade, we’ll have evidence for, or against our hypothesis, and we’re excited to see it tested. And so science works in this beautiful way that we’ll be able to falsify and determine, which is the leading explanation, and we’re happy by this to know, is it comets that could help us understand how water got on earth or is it these more perplexing processes? And really altogether, it’s just the pleasure of finding things out, and so that’s really driving us, is to seek the unknown and dare to discover.
Vicky Thompson: 20:48 The end of the decade, that’s pretty soon in the scheme of science.
Sara Whitlock: 21:01 It is, we’ll know how the moon snatched its ice in no time and having ice water on the moon is actually useful for a lot of different reasons.
Kathleen Mandt: 21:08 So there’s two different reasons to be excited about ice on the moon, for me personally, it’s science. The ice on the moon is a record of the history of volatiles in the earth moon system, so whatever’s been impacting the moon over the history of its existence has also been impacting the earth.
And impacts on the earth’s surface have mostly been erased by the processes that take place on the surface of the earth that allow us to live here, which I don’t want to change that, but we have these volatiles stored on the surface and in these permanently shaded regions of the moon that have been stored there for millions to billions of years, that provide us with a time capsule of the history of our system and can tell us what has been delivered to the earth throughout its history that has helped to support life.
Like, we need water for life, so this source of water is important for us to understand, so that’s one of the things that is really exciting about water and other volatiles on the moon. The other thing that is exciting is that it does create an opportunity for a resource for human presence on the moon long term, which I am also really excited about, and I would love to see humans on the moon on an ongoing basis, doing science, doing exploration, and just bringing to life, these science fiction stories that many of us enjoy reading.
Sara Whitlock: 22:48 Do you think there’s enough ice that we can both use it for human life on the moon and be able to study it?
Kathleen Mandt: 22:55 Yes, because in order to study it, we don’t have to take all of it and then sample all of it and analyze all of it, what we could do is working with humans that are exploring and digging and accessing these resources, is as they access the resources, if you sample the composition as you’re doing so in enough detail, you can still use it because then you’re creating that record that is a record long term that can go for generations to be used for understanding, and it’s the only chance you’re going to get to get that record.
Sara Whitlock: 23:35 That’s super exciting, and it makes me wonder whether astronauts someday will just be able to drill down to these reserves of liquid water and have a well, is that how that would work?
Nicholas Hasson: 23:44 Yeah, well, it would truly require new engineering and ingenuity and that’s what’s so cool about science and about particularly NASA, is that it’s like, “Dare to discover,£ because when we discover new things, we always come up with new ways to develop those resources.
So technology means the manipulation of physical phenomena, so when you find a new physical phenomena, like, say, aquifers on the moon, how would you pull that water up? It’s so cold on the moon and so hot, depending on the orientation with the sun, and furthermore, there could be new technology, like I was talking about ion traps, it’s potentially possible that we could actually harness some of the active ions coming from earth to form our own water, so if you’re getting oxygen and you’re getting hydrogen and you form, OH, you can bond the oxygen with the hydroxyl radical and potentially garden water from the earth atmospheric escape.
Sara Whitlock: 24:55 So instead of maybe carrying our own water, we could cast some sort of net and catch water from the earth as we go by?
Nicholas Hasson: 25:01 That’s right.
Sara Whitlock: 25:03 And it sounds like we wouldn’t have to worry about running out of water on the moon if your ideas about the escape from the earth’s atmosphere are correct for where this water is coming from.
Nicholas Hasson: 25:13 That’s right. And just to be clear, the atmosphere is losing a very minute amount of oxygen or part of its atmosphere, and so this process is likely very slow, whereas, previous hypotheses that are, I think, more well-developed, like chondrites and comets, bringing water there, those would deposit significant amounts of not just water, but other rare earth metals in this case, rare lunar metals.
And so, what’s waiting for us in the subsurface of the moon? Is it aquifers? Is it helium-3? And so the moon is of our extension of earth, and it challenges the notion that in the ’70s was popular, that there’s limits to growth on earth, we’re going to run out of resources, and we got to be sustainable, which is valid and sound, but now, we realize the moon may have all of this potential energy, for example, helium-3, water deposits to make propellant.
Some people like to say the moon will be the industrial zone of earth one day and earth will be a giant garden or a park, so the moon offers us a way to grow from this planet, but the evidence shows that the moon is actually an extension of earth, both geologically and potentially actively part of our hydrosphere and cryosphere.
Sara Whitlock: 26:49 I guess that would argue though, that we should be thinking about conservation on the moon as well, right? Rather than just outsourcing all of our mining without thinking about it.
Nicholas Hasson: 26:59 That’s a really good point because whatever you do on the moon, it’s going to stay put because there’s no way to kind of wash away the activity, so that’s really opening up all of these topics about who owns the moon, what will we do there? How do we conserve areas of the moon or how much activity do we want to do there?
I mean, very rarely will you hear people talk about this, other than in these very highly technical fields, and so really, I think this is a dawn of a new era for the moon, the moon has always been there romantically, we even call crazy people, “Lunatics,” right? And so what kind of folklore and what kind of values and ethics will we have in the future, as we learn more about the moon and more about really ourselves in this incredible sort of solar system dance?
Vicky Thompson: 28:10 Conserving the moon, so maybe someday we’ll have Moon Day, but not just an anniversary celebrating the moon landing more like a version of Earth Day where we can serve the moon’s resources.
Sara Whitlock: 28:22 Wait, we have a slogan for moon day? Isn’t the one for Earth Day, “Make everyday Earth Day?”
Shane Hanlon: 28:31 “Make every other Day Moon Day,” is that-
Vicky Thompson: 28:39 “Make some days Moon Day?”
Shane Hanlon: 28:40 “Make some days Moon Day.” That’s real bad, we’ll work on that one, maybe someone else could help us out with that.
Vicky Thompson: 28:46 Let’s circle back.
Shane Hanlon: 28:48 But in the meantime, that’s all from Third Pod from the Sun.
Vicky Thompson: 28:52 Thanks so much to Sara for bringing us this story, and to Kathy and Nick for sharing their work with us.
Shane Hanlon: 28:58 This episode was produced by Sara with production assistance from Jace Steiner and audio engineering from Colin Warren.
Vicky Thompson: 29:04 We’d love to hear your thoughts on this podcast, please rate and review us, and you can find new episodes on your favorite podcasting app or at thirdpodfromthesun.com.
Shane Hanlon: 29:13 Thanks, all. And we’ll see you next week.
Sara Whitlock: 29:20 Her paper’s based on a NASA experiment where they crashed a rocket from a ship called, “The Lunar Crater…” Oh, no, that was bad.
Vicky Thompson: 29:31 Oh, no.
Sara Whitlock: 29:31 It’s like coming out, I was just like, “Oh, no.” Lunar Crater-
Shane Hanlon: 29:34 Oh.
Sara Whitlock: 29:35 … Observation and Sensing Satellite. Okay. Whoo.
Shane Hanlon: 29:37 That’s amazing.
Vicky Thompson: 29:38 Wait, is the sentence that I said is grammatically correct?
Shane Hanlon: 29:42 “How scientist figure out which of these different sources was how…”
Vicky Thompson: 29:46 “Was how-”
Shane Hanlon: 29:46 “Was how-”