Ep. 686: Ice in the Shadows

The permanently shadowed craters on the Moon are the focus of so much research. That’s because they seem to contain vast reserves of water ice. Water we could use for oxygen, propellant and so much more, but also, to help us understand where the Earth’s water came from.


(This is an automatically generated transcript)

Fraser Cain [00:01:35] Astronomy cast. Episode 686 ice in the shadows. Welcome to Astronomy Cast for weekly facts based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, I’m the publisher of Universe Today. With me, as always, is Doctor Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. How are you doing? 

Pamela Gay [00:01:57] I am doing well. It is a Monday. It is nearing summer hiatus, which I am actually sad about because I do enjoy getting to hang out with you every single Monday. But at the same time, like, my yard is green and it is warm. And yeah, these are all good things. 

Fraser Cain [00:02:17] Your bike is calling to you and yeah. Yes, yeah, yeah, I’m exactly the same way that there are all of these things, you know, like my dad wants me to come over and visit and I’m like, well, dad, I can, but I’m busy on Mondays and I’ve got to get I got to be near high speed internet, and I got this thing I got to do on Tuesday. I got an interview. On Wednesday, I got this other thing I didn’t. And then Fridays I do this other thing and, and and so nope. Now just day after day after day of sort of internet free existence where I can do work, but also be going places and seeing people. So no, I think it’s great. I, I hope that we are an inspiration to all of you to take a break. Yeah, you can or at least get away from the internet if you can highly recommend it. But yeah, so we have this episode, two more episodes, and then we are on summer hiatus. So just like whatever you need to do to come to grips emotionally with what’s about to happen, go to your happy place because it’s coming. The permanently shadowed craters on the moon are the focus of so much research. That’s because they seem to contain vast reserves of water, ice, water we could use for oxygen, propellant and so much more, but also to help us understand where the Earth’s water came from. Why? How could there, I guess why would we not expect there to be water? First, let’s start with this. Why would we not expect there to be water on the moon? 

Pamela Gay [00:03:50] Oh. Pretty simple. The moon doesn’t really have an atmosphere, which means liquid will evaporate away instantly. The surface of the moon, when exposed to sunlight, exceeds the melting point of water. So if anything hit by sunlight melts and anything that melts evaporates away and there’s no atmosphere. So anything in the very tenuous, exosphere, it’s not fully an atmosphere, will get blasted away by, like, solar, wind and stuff. Water is not going to hang around in general. 

Fraser Cain [00:04:31] And so why do we think that there are reserves of water on the moon? 

Pamela Gay [00:04:37] Well. 

Fraser Cain [00:04:38] Or I guess why did we think so before we confirmed them? Why did we think there were. 

Pamela Gay [00:04:44] Good. 

Fraser Cain [00:04:44] Catch? Yeah, yeah, yeah. 

Pamela Gay [00:04:46] So it was realized that, well, our earth is tilted about 23 degrees. And so as its orientation relative to the sun changes throughout the year, everything gets struck with sunlight, pretty much, there’s bottoms of wells and things like that that can avoid it. But on the surface, you’re pretty much good to go with. Everything will get sunlight. The moon, however, is only tilted like a degree and a half, and that little tiny tilt means that there are craters on the north and south pole that when you start working out the geometry and the depth of the craters, the sun literally doesn’t shine there. 

Fraser Cain [00:05:32] Ever. 

Pamela Gay [00:05:33] Ever. 

Fraser Cain [00:05:34] Yeah. 

Pamela Gay [00:05:34] You can go to the place where the sun don’t shine, right? 

Fraser Cain [00:05:37] And it’s weird because you can also go to the place where the sun always shines. 

Pamela Gay [00:05:41] Exactly. So there are peaks at the North and South Pole that are always in sunlight. And one of the coolest things about this is those regions that are permanently shadowed are like 25 to 70 degrees Kelvin, but they’re thermally stable at super cold temperatures. And those regions that are permanently in sunshine, they’re super hot, but again, they’re thermally stable. 

Fraser Cain [00:06:10] Yeah. All right. And so then how do we know that there is ice in these shadow craters? 

Pamela Gay [00:06:19] Because we bombed the moon in 2009. Now, that wasn’t the phrase that we used. That is the phrase Twitter used. The Lunar Reconnaissance Orbiter didn’t launch alone. It launched with a companion mission cross, where they essentially took a empty stage from their spacecraft, careened it into a South pole crater that had permanently shadowed regions, and El Crossed followed in that stage, flying through the debris cloud, looking to see what was present and measuring as it went. And what it measured was hundreds of kilograms of water vapor in that plume. 

Fraser Cain [00:07:05] And I mean, that’s I mean, that was amazing. But actually, the first spacecraft to discover water on the surface of the moon was India’s Chandrayaan one mission, which had a, a bunch of instruments on board, including a NASA instrument. And it was with one of those instruments, they were able to, to detect the presence of water on the moon. 

Pamela Gay [00:07:33] And, and that was a more tenuous. So, so that that was looking at what is the distribution of, I believe it was neutrons in the surface where when the sun has a flare, the high energy photons can cause neutrons to get bounced off. There are effects and things and stuff that the instrument can then detect. And because water is two hydrogen atoms and then that one oxygen, they tend to have a high ratio of neutrons to protons. And those neutrons can be knocked off fairly easily. So where you see a high density of neutrons beneath the surface, it is considered to be a reflection of a high amount of water being present. But the question was is it water for sure? Is it for realsies people? So it has to be confirmed. And the other question was, so you can have water that is locked up inside minerals and not necessarily accessible. And so if it is water, is it accessible water. 

Fraser Cain [00:08:45] So let’s talk about like as you say, the presence of like the presence of hydrogen was detected in these rocks. And there were other substances each for example. Yeah. Hydroxide or anything. It’s called. 

Pamela Gay [00:09:03] Hydroxyl groups. Yeah. 

Fraser Cain [00:09:04] Yeah, yeah. Like there are other things that look like water but they’re not water. And you know, you could do some chemistry to turn them into water, but they’re not just ready to melt and drink. Right. So I guess when do we figure out with much more certainty that there is indeed water, both in the permanently shadowed craters and even other parts of the of the moon, as you say? You know, we excavated some, we did some. 

Pamela Gay [00:09:32] So El Cross was kind of the way. Yes, yes, there is water that will end up in the in the plume created when you excavate into a permanently shadowed region. And since then, researchers have been working to figure out how to use different instruments to study how it is that water could first get to the moon and once there, migrate so that it builds up in the permanently shadowed regions, because you have two different problems to solve. The first is, is there actually water there? And again, how on earth did it get there? 

Fraser Cain [00:10:13] How on moon did it get there? 

Pamela Gay [00:10:15] Exactly, exactly. 

Fraser Cain [00:10:17] So? So like it? It’s not permanent. It didn’t form with the moon and just never got sunlit on it. 

Pamela Gay [00:10:28] That is true. And then the other thing that we heard was before it was understood just how common this is. It was thought that some of these permanently shadowed regions might have had water left over from whatever impacted into them, and that water was able to just kind of stay put, which really doesn’t make a lot of sense. 

Fraser Cain [00:10:52] Look like a comet smashed into a crater because it hit a shadowed crater. Then the ice remained inside the crater. 

Pamela Gay [00:10:59] Which which doesn’t make a ton of sense when you think through that. The formation of large craters, which are deep enough to have permanently shadowed regions, are going to end up with a lot of melting occurring when that comet hits the surface. And how are you simultaneously melting the regolith and leaving ice bath? Right. 

Fraser Cain [00:11:28] So you’re melting rock, and yet somehow ice is not being thrown away. 

Pamela Gay [00:11:34] Right? So you end up with this very special circumstance of something, goes in, excavates the really deep crater, and then a smaller crater gets formed that doesn’t actually melt stuff, but leaves the ice behind in the exact same spot. And it’s just sort of like, that’s a lot. 

Fraser Cain [00:11:52] Yeah. Like I’m imagining, like taking your frying pan and putting it on a way to hot burner to the point that it’s glowing hot red. And then you let it cool down, you’re like, whoa, there’s water down at the bottom of this. Like, if there was any water, that would have been the first thing to go. Like your pan melted because the water, boiled away. So, so so I guess what do they think is the mechanism that got all of this water into these craters? 

Pamela Gay [00:12:20] So this is one of the coolest things. I’m not a planetary science person, so I’m going to get excited about weird stuff. And this is one of the weird things I get. 

Fraser Cain [00:12:31] This is great. You can be forgiven. 

Pamela Gay [00:12:34] Yeah. 

Fraser Cain [00:12:35] It’s worth getting excited over. 

Pamela Gay [00:12:37] So water gets to the moon via an impact. That part is correct. Now, it also doesn’t stay liquid water. It ends up in the moon’s exosphere somehow. So you either have very small object with water strike surface ice ends up on surface and gets touched by sunlight and. The moon doesn’t have a thick atmosphere, but it does have particles that float around exo spheres. The word I’ve seen used a lot and seen is water. Molecules will rise up into the exo sphere and kind of drift around along the surface and then settle back down re melt. If they get touched again by sunlight, float around and there is the ability for the water to random walk itself into these permanently shadowed regions and then be like, no sun. I stay here and I just kind of love the fortuitous nature of this. 

Fraser Cain [00:13:48] Where you hold on. So you’ve got these comets blasting into the moon. They’re creating this very tenuous atmosphere that contains water particles, and they are sort of vaporized in they are going around the whole moon, and then they wander into this permanently shadowed crater and they go, this is home now. This is what. 

Pamela Gay [00:14:07] Happens. And they just. 

Fraser Cain [00:14:09] And they snow down, know some percentage of them. And yet in astronomical deep time, snow drifts form over long periods of time, like, like even like in some of the driest places in Antarctica where you’ve got these kilometer deep ice sheets, they only get a couple of centimeters of snow a year, and yet it just builds up over long periods of time. A million years of snowfall at that rate gets you somewhere. 

Pamela Gay [00:14:36] The fullness of time is a really amazing thing, and the randomness by which the universe is capable of accumulating ice in permanently shadowed regions is just really kind of fabulous. Yeah. 

Fraser Cain [00:14:52] Yeah. So the focus of a lot of the nations of the world in their space exploration plans are to go to these permanently shadowed craters of the moon. The Chinese have done are planning a sample return mission from the south pole of the moon. They’re planning to send astronauts to the South Pole, the Artemis mission. When they go back with Artemis three, they’re going to go to the South Pole. Like this is going to be the place. Why is it so valuable to go to the South Pole? The moon? 

Pamela Gay [00:15:21] Because there’s ice, we think. And and For All Mankind did an excellent season focused on this. The the idea is we have the South Aiken Basin, which is massive crater filled with craters. There’s a bunch of permanently shadowed regions in here. There’s over 300 known, permanently shadowed regions on the moon as a whole, but the biggest are down in the South Aiken Basin region. And if you have water ice that is accumulating by basically falling out of the exosphere, it’s going to be near the surface. There’s going to be dust. There’s dust everywhere on the moon. And that is the nature of the moon. It’s going to be like the end of winter snowdrifts that are completely covered in site. 

Fraser Cain [00:16:14] Right? 

Pamela Gay [00:16:16] But that’s accessible water without having to do significant mining. 

Fraser Cain [00:16:22] Yeah, I had heard this estimate that, like, we know that there is water mixed in with just the regolith in general across the moon, but it’s like a water bottle for a cubic meter. 

Pamela Gay [00:16:33] Which is that’s a whole lot of energy to liberate that. 

Fraser Cain [00:16:36] Water, right? To crunch it down, to boil off that water and get it out of there. 

Pamela Gay [00:16:41] And so the question becomes, what makes the most sense? Launching water from Earth, flying it from Earth to the moon and recycling it. And no matter how well you do recycling, there’s going to be gradual loss. Then you also have the dig up a cubic meter of regolith. Turn, turn, turn, turn. Get out. Not enough for one day of water or good one of these permanently shadowed regions and hope for baby icebergs. 

Fraser Cain [00:17:22] That would cool. 

Pamela Gay [00:17:23] Yeah. Super cool. 

Fraser Cain [00:17:24] Yeah, 100%. So then I guess, what could we use it for? We got water on the moon. What do we do with it? 

Pamela Gay [00:17:33] So water breaks apart into two hydrogens, which can get used as fuel, and oxygen which can get used as well. We breathe. 

Fraser Cain [00:17:43] It but also fuel like. 

Pamela Gay [00:17:45] But also fuel. 

Fraser Cain [00:17:46] For the. Yeah. I mean like the space shuttle was liquid hydrogen and liquid oxygen was broken up. 

Pamela Gay [00:17:52] Yes. And we need water to drink. We like to have water to clean. Water is a solvent that motivates so many different. Chemical reactions. Water really doesn’t have a whole lot of limits on what you can use it for. Yeah. It is the bringer of life, the bringer of death. If you get excessive amounts right and will dissolve all sorts of things. 

Fraser Cain [00:18:22] Yeah. Dihydrogen oxide poisoning? Yes, exactly. Yeah. And so, like, what would the future of space exploration look like if we’re sort of starting to see into the far future here and we envision like we’ve got. You know, NASA has set up a base, some kind of research station at the near the moon’s south pole. The Chinese have done this. Maybe the Russians have got this. You know, I was looking for all mankind. 

Pamela Gay [00:18:49] Yeah, yeah. 

Fraser Cain [00:18:50] So what are they doing to kind of turn this, these shadow craters into a usable resource? 

Pamela Gay [00:18:56] It’s. It’s not too different from what we do here on Earth with water. You take the water there, you’re going to have to heat it up into a liquid. And then you can use, all sorts of various, basically electronics to zap it apart, process it into whatever you need. But the thing that is most interesting to me, once you ignore all possible political implications of battling over resources, we’re going to ignore that part today. 

Fraser Cain [00:19:25] That will never happen. 

Pamela Gay [00:19:27] Right, right. So the moon is simply the nearest source of permanently shadowed craters. The reason it has them is that lack of tilt. And we have other objects with lack of tilt. The asteroid series has permanently shadowed craters. Mercury. Night. The planets snuggled up right next to the sun. Permanently shadowed craters. 

Fraser Cain [00:19:53] Same thing. Like you could land a spacecraft on Mercury. Just be bathed in sunlight. And then just peep over a crater rim and boom, it never sees the sun. And there is water ice in these. And this has been observed. Yeah. Right. 

Pamela Gay [00:20:08] Yeah. And what’s really awesome about these is on the moon. This is cool on Mercury. This is transformative. If you build your habitat within the permanently shadowed region. It only has to be designed to either keep you warm. Oh, really? If you’re in the permanently shadowed region, that’s all it has to do. It has to keep you warm. And you are hidden from so much of the direct radiation of the sun. And that’s a major benefit. You’re you’re not directly in that ionizing radiation. Then you have all of these resources there. And the top of the permanently shadowed crater is likely to have permanently sunny regions where there’s so many different ways to generate electricity, not just solar power. You can start imagining in California, there’s these imagining these amazing liquid sodium reactors that are now using. And you start to be able to imagine doing that kind of energy generation on the moon, then add in to all of that. Now you can also do that on series. You can also do that on Mercury. Now, I don’t know how you get human beings to Mercury in a reasonable way. I’m pretty sure that would kill us, but you can start to imagine getting a research robot there. And that’s just kind of awesome. 

Fraser Cain [00:21:39] Yeah. Yeah I mean who knows. I mean future missions fully fueled up starships have a tremendous amount of delta V. They could throw at it. You could, you could get down to Mercury and and set up shop. 

Pamela Gay [00:21:53] On that radiation field. That worries me. 

Fraser Cain [00:21:57] The radiation fields from the sun. 

Pamela Gay [00:21:59] Yeah. On the way to Mercury because you have to get so close. 

Fraser Cain [00:22:04] But if you’re in a permanently shadowed crater in Mercury and you’re also protected from the solar radiation. 

Pamela Gay [00:22:09] You just have to. 

Fraser Cain [00:22:10] Get there yourself to get there. Yeah, yeah. So does it. Is it really starting to feel like there are more like if it’s always thought that the inside of the solar system was bone dry, and then you get to the frost line, which is like the halfway point of the asteroid belt. And then the outer solar system is tons of ice. Like, you look at the moons of Jupiter. They’re huge amounts of of water ice on them, the moons of Saturn. You’re like all of it. The capabilities, potatoes, ice all the way out there. And yet when you’re inside, bone dry. So it’s starting to feel like there are secret, hidden reserves of water that that we just didn’t realize were there. 

Pamela Gay [00:22:47] I think a better way to put it is it looks like our, our solar system likes to throw snowballs at the inner solar system. And yes, a lot of things were on the surface back dry. But we’re now learning that on the inside they had water reserves. Yeah. And on worlds like Ceres, they’re erupting. All the series is out past the frost line. So different science. But the outer solar system is definitely throwing snowballs, and we’re keeping some of that water. 

Fraser Cain [00:23:20] It’s funny, like I analogy that I was like to think of is like here, like during the long, hot summer, you know, everything is bone dry, all the plants are withering. But you you move a log over. Yeah. The ground underneath is moist still. Yes. And and you don’t. 

Pamela Gay [00:23:37] Have to dig very deep. 

Fraser Cain [00:23:38] Don’t have to dig. Yeah, and plants are peeping out the side of the log because they’re being protected from the evaporation. Permanently shadowed until water can remain there for much longer. It’s. It’s kind of amazing how much water is mixed in and locked away. As long as it gets protected from that sunlight, then it’s here to stay. 

Pamela Gay [00:23:57] And our solar system likes to surprise us by doing things that we didn’t used to think were possible. And it’s going to make it easier for us to explore. Yeah, although I’m sure there are other things that will counterbalance that that also haven’t been discovered yet. 

Fraser Cain [00:24:13] Yeah. I mean, it’s such a gift that that you could launch a spacecraft to the Lunar Gateway area, which is like a gravitational halfway point between the Earth and the rest of the solar system. You you know, you could have mining robots are sending water ice propellant up to the gateway spacecraft dock there, completely refill their tanks, and then do full burn flights to places like Mars or Jupiter or what have you, and significantly decrease the flight time. Have to do that. And it’s like we have this the, the, the idea of this being the gateway, this being this place where you refuel before you head along is we’re so fortunate. And this water ice is going to be the most important piece of the puzzle. 

Pamela Gay [00:25:03] And. And I just want to make it clear. The key is the places that have these have no atmosphere. Venus does not have ice in permanently shadowed regions because atmospheres are insulating. But get rid of an atmosphere and amazing things happen. 

Fraser Cain [00:25:25] Yeah, but like, what else have we got? Like, Titan has an atmosphere and it’s got tons of water ice. 

Pamela Gay [00:25:29] Ice Titan doesn’t exactly have an atmosphere that is above the temperature. Freezing. So great small gifts for small. 

Fraser Cain [00:25:36] Yeah, yeah, yeah. All right. Thank you much. 

Pamela Gay [00:25:39] And thank you, Fraser. And thank you to all of the folks out there who are part of our Patreon. You lovely souls. Get this advertisment free. This week I would like to thank Boogie Net, Balthasar Jones, Jean-Baptiste Lee Martin, Daniel Donaldson, Frank Stewart, Christian Golding, Wil Hamilton, Michael Hodo, Jarvis Earl Galactic president, superstar mix scoops a lot. I love that name. Yeah. John Bass brewery. Gawain. Stephen. Vite. Jordan. Young, Zeenat. Wink, Andrew. Astra. Brian. Kegel, David. Trude. True. Boogie. Net. Gerhard. Shrike. Short. Sir. David. Buzz. Parsec. Zero. Chill, Greg. Davis, Laura. Kelson. Les. Howard. Robert. Plasma, Joe. Holstein, Frank. Tippin, Gordon. Davis, Adam. Annis. Brown, Richard. Drum, Alexis. Felix. Scoot. Wanderer, M 101 Astor. Sets William Andrews gold, Roland. Warmer, Dom Jeff Collins, Simon Parton, Kellyanne and David Parker, Jeremy. Kerwin, Stuart Miles, Baltasar Jones. Thank you. 

Fraser Cain [00:26:57] Thanks, everyone, and we’ll see you next week. 

Pamela Gay [00:26:59] Buh bye everyone. Astronomy cast is a joint product of the Universe Today and the Planetary Science Institute. Astronomy cast is released under a Creative Commons Attribution license. So love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you. Thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast. 

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