We’ve talked about water on the Moon many times here on Astronomy Cast, but there have been a bunch of big updates, thanks to new research from NASA and others. Today we’re going to give you an update on the state of water on the Moon and the plans to take advantage of it.
What is LCROSS, the Lunar Crater Observation and Sensing Satellite? (NASA Ames Research Center)
Hydroxy group (Wikipedia)
Water on the Moon (ISRO)
Ice Confirmed at the Moon’s Poles (NASA Ames Research Center)
Neutron spectroscopy (Science and Technology Facilities Council)
NASA’s Spitzer Space Telescope (Caltech)
Hubble Space Telescope (Hubblesite)
Absorption/emission lines (Khan Academy)
South Pole – Aitken Basin Landing Site Database (Lunar and Planetary Institute)
Here’s how we could mine the moon for rocket fuel (MIT Technology Review)
VIDEO: Interview: Alex Ignatiev and Manufacturing on the Moon (Fraser Cain)
The Expanse (imdb)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast Episode 589. Lunar Water Update. Welcome to Astronomy Cast. Our 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, publisher of Universe Today. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of CosmoQuest. Hey Pamala, how you doing?
Dr. Pamela Gay: I’m doing well. We are almost done with this year that shall not be named.
Fraser: Yeah. 2021’s gonna be so much better.
Dr. Pamela Gay: I don’t anyone agree to hold its beer. That’s all I have to say.
Fraser: 2021 is gonna be the same. It’s gonna be like the recovery from 2020. We got some fixing to do. It’s gonna be a lot of work to get everything reorganized. But I have hopes.
Dr. Pamela Gay: As long as all the slopes are in the correct direction, because right now all the slopes are in the wrong direction.
Fraser: Yeah. I think they’ll go in the wrong direction for a while in 2021 too. But we’re gonna go out with a bang, which is gonna be the Great Conjunction. Saturn-Jupiter, just within a couple of arc minutes of each other.
Dr. Pamela Gay: Arc minutes. Six arc minutes.
Fraser: And that’s gonna be on the 21st. And so, hopefully, you’re gonna be getting this on the 21st, on the morning of the 21st. And so, we just wanna give you one last reminder that this is your chance to see Jupiter and Saturn in the same telescope eyepiece.
Dr. Pamela Gay: And this is something that folks are already pulling off. They’re already close enough, and they will remain close enough for a little bit afterwards. And what’s amazing is this won’t happen again in our lifetime. And, in fact, the last time these worlds lined up this close together on the sky, no one got to see it. It was 400 years ago. And the objects were positioned such that you had to know where to look during the day. And 400 years ago, people weren’t looking during the day for Jupiter and Saturn.
Dr. Pamela Gay: So, instead we have now. We have only now. It’s winter in the north, but hopefully we’ll get some clear skies. I for one am gonna try and pull out telescopes this weekend.
Fraser: Yeah, and we’re gonna try to do a livestream of it, so that if you’ve got bad weather or no telescope, then you can see it. But, as everybody I hope has learned at this point, our ability to pull this kinda thing off is tough.
Dr. Pamela Gay: Yeah.
Fraser: Live astronomy is the worst. But we will do what we can. All right, we’ve talked about the moon and its water many times here on Astronomy Cast, but there have been a bunch of big updates thanks to new research from NASA and others. Today, we’re gonna give you and update on the state of water on the Moon, and the plans to take advantage of it. Water on the moon. All right Pamela, is there water on the moon?
Dr. Pamela Gay: Yes.
Fraser: Okay. So, you got some patrons for us this week? No. All right. So, up until the fairly interesting research that came out earlier this year, what did we think was the state of water on the moon?
Dr. Pamela Gay: So, we believed from the 2009 LCROSS data from when we essentially threw part of a rocket at the moon and then measured the contents of what it tossed up into the air on impact – we believed from that experiment that there was either hydroxyl groups or water ice. And we thought it was water ice mixed into the regolith on the moon.
Fraser: So, what’s a hydroxyl?
Dr. Pamela Gay: So, a hydroxyl is an OH group. It is something that is almost a water, but you can’t drink it.
Fraser: Don’t drink it. Right.
Dr. Pamela Gay: So, we thought there was either of these OH groups, which are energetically very similar to water but not exactly drinkable, or that there was water ice mixed up in the soil. And this is one of those frustrating things of, “We impacted the moon to stir this stuff up, so where, how deep, how far down do you have to go? How hard is it to get out of the minerals?” All these things were the questions that came out of that 2009 experiment.
Fraser: And, I think, we had known that there was significant amounts of water ice at the poles of the moon. The Chandrayaan mission had helped map out the location of the water in the moon’s permanently shadowed craters. And it’s thought there’s even deposits. But what LCROSS helped to show was that there’s actually water significantly away from the poles of the moon in areas that are lit by sunlight constantly, and this water should have been evaporated off into space.
Dr. Pamela Gay: And this did it in a way that was more certain about what was being looked at. There’s lots of ways to try and detect if water is there. One of the easiest ways – and this is something that we’ve done on Mars, on the moon, don’t need to do it on Earth. We know we have water. The technique is to look for neutrons. Neutron spectroscopy. And these can get scattered when a cosmic ray, a high energy particle, impacts with water. Now, unfortunately, it can also maybe happen with other reactions. So, when we are detecting these neutrons, it’s not for certain that it’s water. It’s for probably it’s water. And that’s less satisfying, and that was the point we were at in 2009, was there’s probably water. Theoretically, there should be water in these permanently shattered regions.
Fraser: Yeah. But, “Take a water bottle and hope” is not a good way to explore, right?
Dr. Pamela Gay: No, it’s really not.
Fraser: You want that certainty. Okay, so then 2020, we got an update to this story.
Dr. Pamela Gay: We did. And this was data that came to us from SOFIA. Now, between 2009 and 2020, lots of different people had been looking in different ways, including spacecraft on their way to other worlds, to see if they could see the spectral signature of sunlight being reflected off the moon in a way that said, “Hey, there’s water that is interacting with these photons. Look here, there’s water.” And, unfortunately again, we’re back to that confusion of, “Is it water, or is it hydroxyl groups?” Which we had earlier. And, so, while we had intermediate measurements that were probably water, they weren’t necessarily water until a graduate student working with the SOFIA team said, “Hey, while we’re transferring the aircraft from one point to another and don’t have science planned, can we look at the moon? Can we look in the infrared at this one particular molecular line that is indicative of water and only of water.”
Fraser: Ok, I need you to do two things now. One, you need to explain what SOFIA is.
Dr. Pamela Gay: So, SOFIA is an airborne observatory. It’s a 747 with a hole cut in the side, and a telescope that can stick its shutter in that hole and capture light. And this 747 flies high enough up in the atmosphere to get above a lot of the water and other things that prevent us from being able to do a lot of infrared observations here on the surface of the earth.
Fraser: And that’s leading into my second question, which is why was SOFIA the right tool for this job? Why could only SOFIA have been able to detect this water? You would think that there would be all kinds of telescopes on Earth that would be able to find this. Why SOFIA?
Dr. Pamela Gay: Well, unfortunately, our atmosphere has a lot of water in it. And that water is at the same wavelength that water on the moon is at, so we can’t see it from here. And it requires a cooled telescope. Spitzer ran out of coolant a long time ago, and during its cold phase, never looked for this particular line. And there just hasn’t really been anything else capable of making these observations.
Frasier: And so, you’ve got this – and if you haven’t already, you really should take a look at a picture of SOFIA, because it is a mind-bending piece of engineering. I forget how big the telescope is. Big. Several meters. Three meters? Four meters?
Dr. Pamela Gay: I don’t think it’s that big.
Fraser: Yeah. It’s a big telescope housed in this rear of a 747. And it’s got a beautiful mount that keeps it perfectly stable as the aircraft is flying really high. Above as much of the turbulence as possible. And for hour after hour after hour, they’re making these telescopic observations at this wavelength that no mountaintop observatory can view. Only a space-based observatory could do this. And so, you’ve got this best of both worlds where you’ve got the ability to come back down, modify your instrument, attach different science experiments, download your data. Whatever you need to do, but at the same time, you’re able to get above most of the atmosphere. It’s essentially the most pristine view you could have. It is halfway to a space telescope. And it is a wonder of engineering. It is one of my favorite instruments.
Dr. Pamela Gay: And this is a 2.7 m mirror. Nine feet essentially across, just for the mirror. And so, this is a massive system.
Fraser: Yeah, so that’s like a little bigger than Hubble.
Dr. Pamela Gay: Yeah. And it flies on a 747. And so, it has one of the coolest instrument stability systems that has been built by humans. And it’s capable of doing things that currently nothing else can do.
Fraser: Okay, so during this flyover, this redeployment, they took some imaging of the moon, and what did they find?
Dr. Pamela Gay: They saw that absorption line in the spectra. And the scattered light from the sun that was reflecting off of the moon, that indicated there was water absorbing the sunlight, and it told us that in the mid-latitudes, not at the equator, they looked a couple different places. They did not find water at the equator. But at the mid-latitudes, there is water in the regolith and the minerals that is absorbing that particular color of light that only water absorbs out of the scattered sunlight.
Fraser: And so, they were able to confirm, and so essentially, distinguish between water and that poisoned fake water.
Dr. Pamela Gay: Hydroxyl.
Fraser: Yeah. Okay, and so then, were they able to get a sense of how much water there is?
Dr. Pamela Gay: So, it doesn’t look like a lot. It’s kind of like a soda bottle’s worth every few sq m of dirt.
Fraser: Right. I had heard that compared to a fraction. Even the Sahara Desert. The driest parts of the Sahara Desert has more water mixed in than the moon. But it’s not zero.
Dr. Pamela Gay: It’s not zero. Now, what we don’t know is how mixed into the minerals it is. So, is this as- has been theorized to be able to form rocks of ice that are covered in dust, and thus partially protected? Is it individual molecules of water that are trapped inside the grains that would be super hard to extract. And it’s in try to find out how hard it is to get this water out that it starts to become a, “Well, can we rely on using this water, or is this just neat chemistry that we know happens to be true?”
Fraser: Right. So, then, I think when you had cued up the topic for this week’s episode, you had said Water and other volatiles. So, I think we sort of follow the conversation back. If we went back to the beginning of Astronomy Cast, I can’t be certain, but I would assume that the conversation was something like, “The inner solar system is bone dry. The outer solar system has lots of water. Water and other volatiles are gonna be really precious.” But now we know that in fact, there’s a surprising amount of water. We’re seeing this with the LCROSS impact, we’re seeing this with the sample returns that have come back from Hayabusa, and we’re going to assume from OSIRIS-REx as well. That it really looks like these asteroids have a surprising amount of water and other volatiles inside of them that will be- that could be used – well, like 1. To help you learn about the early solar system, but also 2. To use these as resources to be able to support exploration and so on. So, at this point, what do we think? How much of these other volatiles are there?
Dr. Pamela Gay: Well, we’re pretty sure that there is the Helium 3 that we’re looking for. We’re pretty sure that there’s probably some ammonia in there, and basically if something existed on a comet, it’s probably somewhere in the moon. And this is where we get into the really interesting physics of what are called “cold traps,” which feel particularly timely with the movie Dune coming out, which I may be a little overexcited to get to see. So, any of you who’ve read the book or seen earlier versions of trying to make this into a movie or a miniseries know that the desert world Arrakis has these catch traps that the wind blows in against the rocks, gets cycled down someplace cooler, and any moisture trapped in the air condenses out, and forms essentially ponds, puddles, depending on size, within these cold traps. Well, that’s what happens when you have an atmosphere and warmth. Moon has no atmosphere. It has warmth in sunlight, but not in shadow. And so, what can happen on the moon – and we’re now realizing this can happen at all scale sizes – is you can have something deposit water on the moon. So, incoming comet, incoming asteroid, and the volatiles that are deposited on the moon. The Carbon Dioxide ice, the Carbon Monoxide ice, the water ice. It can get excited, it can get sublimated, it can float around as individual particles in the atmosphere of the moon, and then settle down. Now, if where it settles down happens to be a cold trap, it just stays there. It’s not leaving. And it can build up over time. And if it settles someplace that isn’t a cold trap, it’s gonna keep moving Brownian motion, until eventually it ends up in a cold trap. And so, essentially what happens is all of these materials that sublimate away in sunlight will end up migrating to someplace cold where they can settle down to stay.
Fraser: Right. And when you say cold, is that the poles of the moon? Like those permanently shadowed craters, or are there other regions where we could find this as well?
Dr. Pamela Gay: Well, you can end up with permanently shattered regions in all sorts of different places. So, while we primarily think of the massive permanently shattered regions, particularly in the south pole Aitken Basin, where the geometry of the sunlight coming in at the equator, and glancing over the top of the moon means that anything below the horizon is going to be in shadow forever. That’s easy to understand, but we’ve all gone outside and dug a little hole that the sun never shines directly into.
Fraser: Sounds like our last week’s episode.
Dr. Pamela Gay: So, you can have these little holes of all sorts of different sizes. And they could represent places where water can stay. And it’s now estimated that order of 15,000 sq kms of the moon may be capable of trapping water.
Fraser: Wow. And so, there could be these deposits, these cold traps across the moon that you could be finding. And so, all of these impacts that are happening on the moon are releasing these volatiles, they’re finding some other spot, they’re condensing again, and they’re just waiting for people to go and find them. That’s super amazing. So, then what would it take for us to be able to get our hands on them. Because I mean, we’ve talked about this in the past. That water and other volatiles are a really critical piece to being able to continue your space exploration. To essentially refuel at the moon, you need water. Split it up. Hydrogen, oxygen, you’ve got rocket fuel. What would it take to get our hands on this stuff?
Dr. Pamela Gay: Well, this is where it gets to the, “We don’t know.” What else is bouncing around in the atmosphere? What else is in the cold traps? How does the moisture get layered? Are there any chunks of comet left hanging out in the bottom of a crater somewhere? We don’t know the answers to these questions. And there are models that basically say that some of these smaller cold traps may literally have essentially a rock of ice. But that’s not all the models. That’s not a consensus view, that’s a “We don’t have enough data to know what is most likely.” And so, while this may be possible, it could be that we’re gonna essentially have to do like we do when we’re processing ore here on Earth. You dig up a whole bunch of soil, you- well, in this case, bake it. Which is a highly energetic process, grind it up, and between the grinding it up and the baking it, you can release the volatiles. Again, highly energetic process. Not cheap. Cheaper maybe than carrying all of our water with us.
Fraser: Right. I guess that’s the point. If you’re look at $1 million a kilogram, or whatever it’s gonna cost to carry stuff all the way from the earth to the moon, then setting up some kind of machine that bakes- it was interesting, I did an interview with a scientist who’s developing a method to develop solar panels on the moon. And he was saying, “The first thing you really need on the moon is energy, and the second thing you need on the moon is energy, and the third thing that you need on the moon is energy.” And you can absolutely see that with being able to bake regolith to get at the volatiles, to these various ideas to turn regolith into bricks, to high-heat extract aluminum and titanium and all of these minerals that you might want off the surface of the moon. I’m gonna rabbit hole for one second here. People talk about this idea of mining the moon, and how difficult it’s gonna be to- or the incredible potential it’s gonna be for mining the moon. The moon is the worst.
Dr. Pamela Gay: Yes.
Fraser: It’s just terrible. It’s just a tangled shredded wasteland of glassy-
Dr. Pamela Gay: And it has more gravity than we want. It has too much gravity.
Fraser: Yeah. And so, it would be like trying to drink in the middle of the ocean. It would be like trying to grow in the middle of the desert. It’s terrible. No, we don’t want any of what the moon has to come back to Earth. But if all you’ve got is the moon, it beats the alternative of trying to bring this stuff from Earth.
Dr. Pamela Gay: And this is where ideas that have been going back for decades and decades, and that we currently see in TV Shows like The Expanse, which is also back with a new season which I am excited about.
Fraser: Except only three episodes. That is unkind. Let’s just say that things descended into chaos around the whole Cain household after we only got three episodes. One night, things were fine, we were in our new episodes, those are dark times.
Dr. Pamela Gay: Yeah. So, I’m gonna probably binge watch tomorrow using the Twitch watch feature, but that’s a different story. The story that I wanted to reference was one of the things that we see in The Expanse is this idea that there’s a whole lot of icy objects out there that aren’t very big. And we may in the future be able to go out and take these lower mass objects, mount engines on them, and move them where we need them. And it may be easier to build a fuel depot just beyond Earth, and use that instead, and not deal with the moon’s gravity at all.
Fraser: Wouldn’t it be cool if there was a comet that had been brought into the inner solar system that was, say, on a co-orbital position with the earth, and so would always be there at the Lagrange point, and it would be this permanent bright comet that’s always in the sky. And you would look at that, and you would say, “That is our fuel depot.” And yet, it would also jut have this enormous cometary tail trailing off behind it. Because it would be in the inner solar system, and it would be not even. It would be just a few hundred million km from the earth. It would be amazing.
Dr. Pamela Gay: So, I’m gonna say something I don’t think I’ve ever said to you before. You’re thinking too small.
Fraser: Oh, okay! Wow. Wait, what? That’s impossible!
Dr. Pamala Gay: So, one of the awesome things about orbital dynamics is if you put something in a slightly bigger orbit than the earth, it’s going to orbit more slowly. This is why we lost track of – well, we didn’t lose track of – this is why we lost ready communications with Spitzers that trailed behind us. Now, imagine that you grab five or 10 objects, distribute them equally, and a slightly larger orbit so that we’re always leaving one behind and moving towards the next.
Fraser: You would have to keep them stable. That would be tricky though.
Dr. Pamala Gay: Once they’re in orbit, they’re in orbit.
Fraser: Yes, but they would crash into each other. They would interact with each other. Are you talking about our orbit, or are you talking about their orbit? Around the sun, or around the earth?
Dr. Pamala Gay: Their orbit. They go in orbit around the sun. On a slightly bigger orbit than we do.
Fraser: Right, yeah.
Dr. Pamala Gay: On a similar ellipticity orbit with the same nodes.
Fraser: Right, okay. I got it.
Dr. Pamala Gay: And so, they should stay reasonably evenly spaced, because their comets are gonna out-gas, or because their icy bodies are gonna out-gas. And that is what you have to counteract.
Fraser: So, there will always be a bright comet in the sky, with an enormous tail, and that is a symbol of humanity’s gateway to the exploration of the rest of the solar system.
Dr. Pamela Gay: I think you’d probably want to eventually coat them over to stop the out-gassing, but the building of this system would be amazing.
Fraser: Yeah. I love it. That’s so cool. So, until then, we’re gonna have to go take ovens to the moon, bake the regolith, get at the volatiles and water, and hope to jumpstart that future where we bring in the comets to support the future exploration. I like this bold plan, Pamela. You’re right. I had never even conceived of such an idea. To have multiple ones so there’s one that’s always close. I love it.
Dr. Pamela Gay: Yeah. Basically, communication satellites that have water and allow us to communicate around the entire solar system. We’re gonna need this anyways. Make it out of stuff we can mine.
Fraser: That’s so cool. Fantastic. Well, do you have some names for us this week? For real this time.
Dr. Pamela Gay: I do. As always, we are supported through the generous contributions of people like you. And, this year, we had seen a decrease in those who are able to support us that we know represents that- a lot of you just aren’t doing okay. And we are so grateful to all of you who are doing financially okay and have taken the time to support us and allow us to just keep paying our humans to help us put together what you see before you. So, this week, I would like to thank Catherine McCabe, Jeannette Wink, Aurora Lipper, Emily Patterson, Just Joe, Ed Loves Science, Helge Bjørkhaug, Gordon Dewis, cacoseraph, Joshua Pierson, Bill Hamilton, Frank Tippin, Richard Rivera, Alexis, Jack Mudge, Thomas Sepstrup, William Andrews, Jeff Collins, Harald Bardenhagen, BenFloss, Marek Vydareny, ArcticFox, Ron Thorrsen, Nate Detwiler, Phillip Walker, Martin Dawson, Brian Gregory, and Elad Avron. Thank you all so much for being here and supporting us week after week through the years.
Fraser: And for those of you who are just getting the podcast now, just a reminder this is the last episode we’re gonna be doing for 2020. The next one comes out January 8th. So, you have three weeks to catch up on all the other podcasts that have been filling up your podcast player before the next episode. You’re welcome. I hope you all have a great holiday. Pamela as well. I will look forward to talking to you again in the new year!
Dr. Pamela Gay: See you after the year that shall not be named.
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