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LCROSS Results
Back-to-School Special Transcript

 
LCROSS spacecraft above the Moon's surface

Watch archive of the November 3 Webcast

Read the transcript

Participants:

Tony Colaprete, Principal Investigator

Jennifer Heldmann, LCROSS Co-Investigator

Diane Wooden, LCROSS Astronomer

Brian Day, LCROSS E/PO Lead

Also Available: Archive of the December 2 Webcast

Brian:
Good afternoon and welcome to the Webcast about the results of the mission of the Lunar Crater Observation and Sensing Satellite or LCROSS. We are fortunate to today to have with us key members of the LCROSS science team. At the far end of the table we have the principal investigator for the mission, Dr. Anthony Colaprete, next to him is the astronomer for the mission, Dr. Diane Wooden, next to me here is planetary scientist, Dr. Jennifer Heldmann. My name is Brian Day. I was the education and public outreach lead for the mission.

So this past November we actually had the announcement that water had been discovered on the Moon by the LCROSS impact. That’s pretty exciting. We know more now, but perhaps the best thing to start out with is a little bit of an overview; real quickly, what were the components of LCROSS and how did it work?

Tony:
I can take that Brian if you’d like. I just happened to have a model right here, that’s good! The LCROSS mission was a secondary mission. It flew with the Lunar Reconnaissance Orbiter Mission, which is in orbit still now around the Moon, making lots of measurements, really mapping the Moon at unprecedented detail, and LCROSS road with it. It was an opportunity; they had some extra throw capacity/lift capacity to the Moon, meaning the rocket could carry more than just LRO so NASA wanted to do something with it. So we came up with this idea of LCROSS. You see in this model of LCROSS here, LCROSS is technically just this small satellite rights here, this little spacecraft. It actually connected to the upper stage of the Centaur of the Atlas V (actually the Atlas V took both LRO and LCROSS to the Moon) the upper stage or top part of the rocket had this piece here called the Centaur. The Centaur is about 12 meters long or so and about 2 ½ meters wide. It’s a big rocket. It’s mostly fuel tanks with some large engines on it. Normally this is ditched and it’s dropped into the ocean, burns up on entry, and is thrown away. We wanted to hold onto it and use it as an impactor. So we built, with our colleagues at Northrop Grumman, this small spacecraft. We called it the shepherding spacecraft because it shepherded the Centaur around. I held onto it instead of its being thrown away after it pushed LRO and LCROSS to the moon. We held onto it for four months as we orbited the Earth. And what we were doing there was we were drying this thing out, getting it completely dry, no water in it, no other contaminants as best we could. We calibrated our instruments; on this spacecraft (LCROSS shepherding spacecraft) we had a number of instruments and you’ll hear about the observations from those instruments in a bit, but we had a variety of cameras, and instruments called spectrometers on this spacecraft here.

After four months in orbit around Earth, it so happened that basically the Moon got in our way – Now it was timed just to do that, and that’s how we actually created the impact. We timed our orbits around Earth so that as the Moon came around we came around and met it at the South Pole. What impacted was this part (the Centaur). About 9 hours before impact, we separated from it and turned our instruments around to watch. This piece (Centaur) went into the moon, and came in just like so (this is not to scale, but the way), and we followed it about 4 behind it. So both were moving at about 2 ½ kilometers per second. This impacted the Moon; we observed the impact plume (the ejecta cloud, vapors and whatnot) and the final crater with this spacecraft (LCROSS) and it then eventually impacted the Moon as well. So in a nutshell that was the LCROSS Mission and the hardware involved.

Brian:
Excellent! So, again, last November we found out water was observed in that plume that came up, but I think now we have a better idea of how much, so how much water did come up out of that impact plume?

Tony:
Basically, as Dan put it, I think well: about one us/ one of me -- about 160 kilograms or so in terms of mass of what we saw in our field of view. That may not seem like a whole lot, but when you compare it to the amount of dirt that actually we could see too, it equates to about 5% or so by weight in terms of mixing ratio. So, how much dirt--there’s about 5% of the dirt was actually water ice.

Brian:
That’s a lot more than people think of…

Tony:
Based on observations from hydrogen measurements…we’ve never had a measurement actually of water in on of these craters. So this is the first real measurement of such. We thought there might be something like maybe 1%, maybe upwards of about 1 ½ % perhaps. That assumed that it was evenly distributed in the crater. So we were excited to see that there was this much water, but maybe not necessarily surprised.

Brian:
So Jen, what else did we find besides water ice?

Jem: We found a lot of different types of ices and what we call volatiles, which is a fancy science word, and basically, it just means something, when it’s in the ground on the Moon in these very cold areas it’s a solid, and then when it gets into sunlight or it gets warmed up it turns into a gas. So I think that Diane said it nicely, it’s like something in your house that starts to smell because there are some vapors coming off. So that’s what we talk about as volatile. Tony has some data you might want to show to indicate the different types of materials that were found.

Tony:
Sure, we can describe the spectroscopy of it…That’s one way to go about it and I think we’ve got that video that I showed you a bit ago that gives an example of spectroscopy. Maybe Diane, who is the expert spectroscopist on the team, would like to talk to it….

Diane:
Sure, I’d love to. Well, spectroscopy is a tool where we break the light into its wavelengths, and we look at how the molecules vibrate. Every molecule and every atom has its own vibration pattern. Right here we’re seeing the light curve of how much energy was emitted: First there was a flash. Actually there was duration where we didn’t see any light, and then there was a flash and decay, and from that measurement we know … why don’t you take over here…

Tony:
This is just showing the ejecta plume as it came up into light. This is the Cabeus Crater, and we zoom in and this is the ejecta cloud that we saw at about 20 seconds after impact. That red circle is the field of view of our spectrometers that are making these spectroscopic measurements.

Diane:
And this is a spectroscopy. So the first thing that we do is we try to basically add things together and be a geological sleuth. So here we’re adding water to the continuum of the sunlight and you see that the upper curve is dropping down, better matching. Then we add water vapor, and we get a better match. Then we add some more volatile materials including methanol and C2H2, and we get a best match. So we have primarily water and water ice. But we also have more volatile materials of methanol and formaldehyde and C2H4. This is very exciting because we never imagined we would see these materials besides water. This is a part what we call the curtain phase where the light is not evolving as bright and Tony can describe the figure here.

Tony:
What we did with that spectroscopy you just saw is we can monitor these species over time and see how they’re changing, and that figure you just saw in animation was basically how water vapor was evolving after the impact. In this figure right her you can see it’s relatively low. What we’re looking at here is the depth of one of those features and the spectrum, and the color of light: where there’s water it’s absorbing or eating away a bit of the light, and if we measure how deep that bite is, that’s what shown here and you can see that red line indicates where the impact was relative in time. Before it’s relatively flat, around zero. After it rises quite quickly and it kind of holds steadily over the entire four minute period as we observe the ejecta plume. So, this is how we can determine what’s in a cloud and how much there is and how it’s evolving over time. The rest of this video basically shows the final evolution of the light plume. One of the interesting things, Brian, is that we did actually fly through the ejecta cloud in the very end with the spacecraft, and we were able to detect that ejecta cloud in our instruments, which is really exciting.

Brian:
That is exciting, to actually have the spacecraft flying through this cloud of debris, and when you think of that Centaur that created that cloud of debris, sometimes its fun to think of it as something approaching the size of a school bus, but a school bus moving at 5600 miles an hour. This becomes a fun job!

So it sounds like basically the spectrometers on board the spacecraft broke up the light from that cloud into a series of rainbow colors that actually had the fingerprints, if you will, of all the chemicals that were in that cloud, and then the job that you did was kind of like putting together a puzzle. You take the known patterns of existing chemicals and you fit them together to match the pattern that we saw from the spacecraft. Is that how it worked?

Diane:
That’s right and the finger prints that we saw were not only of water vapor and water ice (icy grains like little tiny ice particles) but we also saw molecules much more complex than what we thought we were going to see, and those molecules are fairly common in comets.

Brian:
Wow. So what do the chemicals that were detected tell us about where the ice and the volatiles came from? Did they originate on the Moon? Or did the come from somewhere else?

Diane:
I’ll take that one. From the abundances that we saw, well, we saw molecules that were very similar to comets. Comets are very good, over the last billion years, comets hit the Moon and the materials would have migrated and gotten stuck in these very cold regions on the poles of the Moon where it’s very cold. We hit the south pole, but it’s true of the north pole also that the sunlight never reaches those craters and so the energy is very, very minimal and they get very, very cold, so anything that gets there sticks and stays. So over the last billion years comets could have hit anywhere on the Moon and those materials would have created a little vapor cloud and the vapor would have hopped and finally gotten into those. So it’s like an attic where the last billion years of what’s been happening we can see what’s there.

But the surprise is that the amounts of molecules that we saw compared to water were higher than what we see in comets. We came to think that maybe these molecules are actually forming in those really cold regions.

Brian:
So there’s actual active chemistry going on, on the surface of the Moon?

Diane:
In these cold regions, over a long time scale.

Another cincher for that idea was the Lunar Reconnaissance Orbiter, which was the satellite attached to here that is orbiting the Moon, they saw at the impact, molecular hydrogen and carbon monoxide and those two molecules are really volatile. Molecular hydrogen is enough to put up airships. So molecular hydrogen would probably not stay around for more than about a million years at the temperature of the cold craters (40 degrees Kelvin). So we know that the material had to have been made there. It’s really exciting that we discovered that on the cold airless body of the Moon, the very harsh environment there actually might be a nurturing place for molecules that are important for life.

Brian:
Wow. That is exciting. One of the things, Tony, that you became kind of famous for before the impact, was describing how the water ice on the Moon might be distributed. I think you used the analogy: smooth style peanut butter versus chunky style peanut butter, so whether the water ice was evenly distributed or located in clumps. What did we find? Do we have an answer to that question?

Tony:
We’re one step closer to maybe understanding the complexity of the question, which is a good way to say: We know for sure now you can’t just say its this way or that way. I think what we’ve learned is that there’s a complexity to the Moon now and in particular complexity to the water cycle on the Moon that we never appreciated a couple of years ago. Where we hit we saw as I mentioned, about 5% water. If you took the remote sensing data, the data from the spacecraft in orbit that tell us how much hydrogen there is (a part of water – water is 2 hydrogen atoms and 1 oxygen atom combined), from orbit we can measure where the hydrogen is, but there’s other things that contain hydrogen and the area over which you measure is very broad, so it’s kind of averaged or smoothed out. So when we were thinking about LCROSS, one of the tests we wanted to make was exactly what you just described: is it uniformly distributed or is it in patches, in pockets. I always think about food, so I use the peanut butter analogy; but another analogy is it a thin frosting, (there I am thinking about food again) like a thin layer of frost or is it ice cubes in the dirt? And if you take our observation, with the latest neutron data (the neutron data is what determines how much hydrogen there is) it points to the chunky model being preferred. There are other observations that support this idea. What we’ve learned about some of the craters is that a lot of the craters at the poles are extremely cold, but a lot of these extremely cold craters don’t show signs of hydrogen from orbit. So it’s not just good enough to be cold, to retain water ice or other hydrogen-bearing species. There are some other observations from radar that also suggest some areas perhaps that have slabs of ice in them. Other observations show large veneers of very small amounts of water even in sunlight. So what we’re learning is, you can’t generalize the Moon, just like you couldn’t generalize the Earth and say it’s this way and only this way. There’s everything from, I think, the very thin, uniform veneers to blocks of ice, perhaps. And LCROSS hit in one of those places where it was rather enhanced.

Brian:
Let’s talk a little more about the nature of the ground that got hit by LCROSS. You mentioned already that it’s probably 5% by weight water ice, but there were a lot of other volatiles there, so how would you describe the nature of the ground that we actually impacted?

Tony: It’s been described in a lot of ways actually, and we were surprised by this, but certainly fluffy.

Diane: Fairy castle-like?

Tony:
Fairy castle-like, yea, and the reason we say that is, we measured the flash of the impact. The flash is a part of the impact that comes out first. The flash, and it happens when all of that dirt and structure from the crashing impactor compress and rub against each other and create heat. You mentioned that we were a fast impactor; we were actually really slow compared to a natural impactor. Meteorites striking the Moon hit ten times faster easily than what we hit, and so the same sized impactor, a natural asteroid impactor would have to be the size of a lemon to generate the same kind of energy we generated with this big rocket. When those things hit that fast, they create a bright flash of visible light, white light. We didn’t see that, and what we saw was a very delayed thermal flash, so we got temperatures up to about 1000 degrees Kelvin, or so. We saw that. But it was delayed from the initial impact time. So what that means to us is we hit into something that was really fluffy, fairy “castle-ish”, and with all these volatiles you might imagine it could be like what’s called it hoarfrost, I don’t know if anyone is familiar with hoarfrost but if you live in areas that have very cool mornings and you get a lot of water vapor in there you can have water vapor freeze and create this very light fluffy matrix. Maybe that’s something akin to what we hit.

Diane:
Is that like when you walk across it, it goes crunch, crunch, crunch?

Tony:
Yes, with a lot of empty space between all those crystals.

Brian:
So 5% of that was water ice. But then there’s all this other stuff mixed in. How much of that was ice of some sort, do we think?

Tony: Diane, do you want to take that? Diane: I think that we decided about 1/3 of it – frozen volatiles, icy stuff. Tony: And those are the things we could see. LCROSS was very specifically designed to look for water, because it was a strategic resource mission for NASA. It really begs the question: What all is in there? You know, if we had better instruments, the right kind of instruments to look beyond what we could see, wonder what else is in there?

Diane:
Some people might ask, “Well, I can imagine what ice is, water ice, and ice cubes, but what other kind of ices?” Well, I know one of them that we often see is dry ice. Like when we’re trying to make a real scary (we just had Halloween), a big scary, you know, fog or something, that’s another kind, that’s frozen carbon dioxide, and so that’s another kind of ice. And if you ever have a chance to crush it with a hammer, it’s not as solid as water ice, so it’s kind of an example of how fluffy friable that is and mix that with dirt, let’s call it lunar soil – it’s not the same as Earth dirt, but lunar soil, and you’re basically going to get a fluffy structure. This is really exciting for us because we really thought it was just maybe a thin layer of powder on something solid.

Tony:
Right, you bring up a good point, I know Jen, you’ve got a lot of experience digging in frozen debris in Antarctica, and if you put a little bit, even 5% water ice in the dirt, it gets pretty firm pretty quick.

Jem:
Very, very hard! So what we’re finding on the Moon is very different from what we find near the poles of the Earth, because when you get water ice in dirt, like Tony said, it’s very hard, but that’s not what we’re seeing here on the Moon. So its surprising that we’ve all looked at the moon, at night, and seen it up in the sky, and you think you know what it is and then we send this mission to the poles, and then we realize, Wow, there’s a lot more that we don’t know and we’re surprised about still.

Brian:
So it sounds like there was a good place chosen to go. This crater, Cabeus, sounds to be a very interesting target. How is Cabeus special? What makes it different than, say, other areas on the Moon, where maybe the Apollo astronauts went? What is so different about Cabeus?

Jem:
If we look at the Moon globe we have here, the Apollo astronauts – the Moon spins on its axis, pretty slowly and it’s pretty much straight up and down, the Moon doesn’t tilt too much, so it’s like this, and the Apollo astronauts mostly went towards the equator, so in this part of the Moon. LCROSS went to the South Pole, so way down here. The poles are very, very special on the Moon: because there’s not much tilt there, the sunlight comes in at a very low angle and some of these craters near the poles of the Moon, there’s no sunlight that’s getting in there for a billion years or more. So if there’s no sunlight that’s reaching there, no direct sunlight, it’s very, very cold. And so that’s why we were interested in going there, because it’s very, very cold, and like Diane and Tony told you, once you have ices and volatiles that get trapped in these what we call “cold traps” the stuff stays there for a long time. And so that’s what we wanted to go and explore.

And then also another thing about this particular Cabeus Crater near the South Pole, as Tony mentioned, we were looking at hydrogen, because we have maps of hydrogen, and we know that water ice is H2O, which has two hydrogen in it, and so we wanted to go somewhere where there was a high hydrogen signal, and that happens to be in the Cabeus region as well. So there are a lot of reasons why we picked Cabeus to go to. And, we haven’t really explored the poles very much before because it’s hard. Imagine you’re working, there’s no sunlight, it’s completely dark. It’s really, really hard to explore.

Diane:
There’s one more reason, Jen, which is that Cabeus is actually not as close to the pole as other regions that show excess hydrogen, so we had a little bit better chance of knowing more about it from Earth’s radar as you’ve already mentioned. And also we were hoping that we would be able to see the plume from Earth-based telescopes, because we would have to be peering over a fairly big mountaintop in front, but we would be looking grazingly in at a crater that wasn’t really right at the poles.

Brian:
So that’s again very interesting in that we had this place that was far enough away from the pole that we were hoping to get a good view, but that it was this very, very fluffy ground that we hit, so when the Centaur hit, instead of bursting into a big fireball on the surface, what happened?

Diane:
It went cush!

Tony:
It went cush! That’s a good way to put it. It went cush. The other thing to keep in mind is the Centaur was a giant empty thermos if you will. They’re big tanks, they’re empty, so this, while it’s big and it’s heavy, it’s mostly hollow, so it’s really low density, so we had a very unique impact – very much not like a normal, natural impact. And luckily we had a co-investigator who worked here at NASA Ames, doing experiments at the vertical gun to test out exactly what happened, but when you have this low density impactor, impacting into a low density fluff you just get all this compaction, everything: this crumples, the ground compresses; and actually what happened was that this penetrated, we think, deep into that fluff and created a vacuum, a pocket behind it if you will, and that creates a cavitation; everything races in behind it to fill in, and that created a jet, if you will, of debris that went straight up, a very thin but fast debris cloud that went up as high as 10 or 15 kilometers, so ten miles up – almost straight up, very narrow cloud. They’ve been able to reproduce that in the lab doing similar shots. So, this was an experiment in a lot of ways. We had to make do with what we had, the space junk that we were otherwise utilizing and went to someplace that we’d never been before. So it was full of surprises. That’s for sure.

Diane:
We’ve still got hot enough to melt glass—I think about 1000 Kelvin, is about 1300 degrees Celsius, which is about the temperature that you might be able to melt glass or blow glass. I just want to make sure they understand, we got hot, but just not that hot.

Tony:
A normal, natural impact would get 6,000 degrees or so or 5000 degrees. We only got to a 1000.

Diane:
So, we’ve already shown pictures of the plume, and I think what you were saying Tony, is that you had some part of the plume that went straight up very narrow, but there’s another part that went out like a blanket and that most of what you saw in that picture was that blanket part, but because we saw material so late, even as late as a few seconds before we impacted, that’s this material that went straight up really far distance and then came down. It took a long time to go up and down. That’s why it was still there when we actually flew through it.

Tony:
And a pencil is an excellent analog because it was pencil thin. That jet that shoots straight up can be very, very narrow, maybe just a degree or two or three. Jen?

Jem:
One to three degrees.

Brian:
So the big question then, based on what you were able to measure in the plume coming out, can you make an estimate as to how much water ice there is in these dark areas or around the dark areas of the Moon?

Tony:
That’s hard as I mentioned, what we learned is it’s not the same anywhere – it’s certainly variable, so there needs to be a lot more work that takes into consideration the new observations from LRO (The Lunar Reconnaissance Orbiter) of hydrogen, of temperature, topography. There’s an instrument called LAMP (Lyman-alpha spectrometer). It looks at starlight and how starlight reflects off of the surface of the Moon, and it’s going to give us some clues as to how this hydrogen is distributed. So it’s going to take time for us to really reassess how much water is on the Moon. In the past we have kind of naively, or just because of lack of data, simply said, “Hey, you have this much dark shadowed area. If it’s at 1%, you have this much water.” Now we know, well just being dark and shadowed is not a sure thing for water ice, and it’s not 1%. Some places are 5%; some may even be more than that. They might be like I said, blocks of ice. So it’s going to take some time to really assess things like that. Now, that said, the area where we hit in Cabeus, the cold area (we hit a place on Cabeus that was particularly cold – less than 40 Kelvin)….

Brian:
How does that compare to like, say the surface of Pluto?

Tony:
It is as cold or colder than the calculated surface temperatures of Pluto. So the Moon is, as the lead for the instrument that measured it put it, Dave Page at UCLA; he said, “As of now, there is no other place in the solar system with a temperature as cold as the Moon estimated.” Now we have not measured Pluto yet. We’ve calculated it. We did the same thing for the Moon: we calculated and found out we were off by factors of 2 in terms of how cold it was. So it remains to be seen, but as of now, the Moon holds the record for the coldest measured place in the solar system. It’s colder than the moons of Saturn, which we have measured the temperatures – that’s why I bring that up. But if you took that area where we impacted and you said, OK, in a 5-kilometer radius around our impact site, let’s say there’s 5% water ice there. It’s about the same as what we saw in a 5-kilometer radius around us. Then in the top meter of dirt you’d have about a billion gallons of water at 5%. It’s not insignificant; it’s quite a bit.

Brian:
So there could be a lot of water there on the Moon.

Diane:
Did you know Brian that water is really expensive to transport to the Moon?

Brian:
That’s probably one of the main reasons that we were interested in finding water on the Moon, right? How much does it cost to get say a gallon of water from the surface of the Earth to the surface of the Moon?

Diane:
Well, since we’ve never done it, we don’t know exactly, but I think I’ve heard…

Jem:
It’s on the order of $100,000 per gallon.

Brian:
That’s for a single gallon, and if some of our students out there some day might be living and working on the surface of the Moon, just think of that: that’s for one gallon of water. You’d probably want a whole lot more than one gallon of water if you’re living and working on the Moon. Water’s important not just for drinking, but breaking apart the constituent hydrogen and oxygen; oxygen you need to breathe – that’s something that you’ll really, really want to do if you’re living and working on the Moon. So water’s clearly a very valuable substance, and having found it in such large quantities on the Moon, that’s exciting. But that brings up another really important question: How has our view of the Moon changed? If you look at how we understood the Moon to be before the LCROSS mission, and now we look at our understanding of Moon, after the LCROSS mission, how has that view of the Moon changed?

Jem:
Before LCROSS we pretty much thought that the Moon was dry, not much water, and then we sent LCROSS, and we found that there’s all of this water ice near the poles of the Moon. So we completely changed our view of the Moon: we went from this dry, barren world to all of a sudden a place that has vast amounts of water near the poles. So that, in itself, is interesting. So we’re having to rewrite the textbooks. The things that you learn in school are changing because of these missions where we go and explore these places where we haven’t been before.

It’s also very exiting too because now, as Diane and Tony were talking about, we found all these other molecules and all these other types of ices in the permanently shadowed region. We didn’t know that those were there before. Now we’re trying to figure out how they got there: was it comet impacts, asteroid impacts, and as we’re learning it’s probably a whole combination of a bunch of different things – a lot of impacts, and also active chemistry going on on the Moon to form these molecules. So now we think there’s an active chemistry cycle that is going on here as well. And then there’s been some other observations of other water across the Moon and what we call OH (hydroxyl). Now we’re talking about a lunar hydrology cycle, which we would never have talked about just a few years ago. Before we sent some of these missions. So our whole understanding of the Moon is changing based on this new data and based on this exploration, which is one of the really exciting parts about doing one of these missions – learning these new things.

Diane:
Wow Jen, you did a great job of summarizing. I’ll just highlight a couple of the things you said, which was in the weeks before LCROSS we found out that there was OH, which is a part of water H2O, so that’s like HOH. It’s just the OH part we saw in the rocks on the Moon, and we didn’t realize so clearly until we hit with LCROSS that there’s water in the form of water, not just water bound in the rocks. So that’s one really important thing and the idea that all the Moon, on the poles of the Moon, it is so cold and so dark (or the fact that it’s dark means it’s so cold) is that there’s actually possible molecule formation. Before this time, we only though those molecules would form in very early stages, before suns and solar systems formed in very cold, dense dark clouds; those are the kind of clouds that obscure the stars along the Milky Way. We thought that that kind of molecule formation happened maybe in the outer regions of our early protoplanetary disk, beyond where Pluto formed, primarily in the dark clouds out of which new suns formed. But here, we’ve discovered that perhaps, those same kind of molecules might be forming on a body somewhat close to our sun in a fairly harsh environment of the strong solar wind, and this is really amazing, because those molecules, if they get evaporated by impacts, which happen all the time, they could become part of other aspects of the Moon, or perhaps incorporated into rocks. It could be delivered by small lunar meteorites to the surface of the Earth. It’s really amazing to discover that chemistry that we thought only happened in really early conditions, more than 5 billion years ago, in a cold black cloud, before our sun was born actually is happening on our Moon, so close to home. So, maybe I’ll pass the ball…

Tony:
I don’t know how I could actually add much to that. I think maybe Jen you said it, we rewrote some textbooks. It reminds me of a story that one of our engineers told us, Steve Board, who said that his daughter had a quiz and part of the quiz was basically, Which of these bodies in the solar system has no water? The Moon was on there and Steve’s like, What do I do here? Do I tell my daughter to know the answer is: Yes, the Moon has water, when they were expecting a “No” of course. So it just goes to show, our thinking about the Moon in the last two or three years because of the literal armada of space traffic that have been there from all sorts of countries: Japan, China, India, the United States has revealed this world that is right there next to us that still remains to be explored. We’ve been to the Moon near the equator with the Apollo missions. The poles of the Moon are an entirely new world, and they’re as rich and as diverse as any part of the world, Earth. So that for me has been the most exciting aspect of the results of the past few years.

Diane:
If you could compare where we hit to any places here on Earth, what kind of water concentration would that compare to?

Tony:
On average, the Sahara Desert has about 2 – 3% in the top meter or so. It’s got a little more water down below, as you might imagine, but that’s one number that I found in the literature was about 2-3% on average for the Sahara Desert. There is a place on the Moon wetter than a place on Earth, which is kind of neat. Kind of amazing, actually.

Brian:
So were do we go from here? What’s our next step?

Tony: One of our next steps is to understand further this water cycle. Jen mentioned and Diane too that there’s OH and water in sunlit parts of the Moon, and that a lot of the things we see trapped in the cold traps, these cold places, are potentially from impacts occurring elsewhere and processes occurring elsewhere on the Moon and those things, those impacts, for example, or chemical processes, causing a migration of materials to these cold traps.

There’s a mission called LADEE (Lunar Atmospheric Dust Environment Explorer) will be launched by NASA in a couple of years and its purpose is to study the very tenuous atmosphere of the Moon. There is an atmosphere on the Moon, it’s really an exosphere, meaning the poor little molecules never really see each other, and in an atmosphere they’ll bump into each other and can say hi. On the Moon there’s so few of them that as they leave the surface they may never see another one again. That’s really a sad life, but it’s a critical life, because those individual molecules, as Diane put it, opting around on the Moon may be part of the process, they’ve certainly got to be part of the process of accumulating these ices and other things at the poles, so LADEE will study that and will study dust potentially lifts off the surface and migrates around the Moon as well, so that’s one extra piece of the puzzle that we’ll be studying soon.

Brian:
Excellent. Now I believe Linda Conrad has some questions that you, our viewers have been sending in.

Linda::
You guys are doing an excellent job of answering the questions before you get them, but just to mention, our friend from India, Dibyendu because he’s been on for several hours and it’s after midnight there, he asked: I want to know the details about the South Pole of the Moon where ice is found. You’ve pretty well covered it, but maybe you want to put a cap on it.

Tony:
A polar cap? Sorry!
If you went back to the image of the dust cloud in that animation, that’s one place we can start. There’s a good deal of material online that you can find if you go to the www.nasa.gov/mission_pages/lcross <http://www.nasa.gov/mission_pages/lcross> webpage under the media tab there’s a headline there about a media briefing, if you click to read more you can see details from all the investigators who contributed recently papers in the magazine SCIENCE, which detail specifically the Cabeus region, which is shown here. So Cabeus is that large crater that you see right in the middle. It’s about 84 and a half degrees south, so it’s about five degrees off the South Pole of the Moon. For those of you who are enthusiasts, Shackleton is another famous crater at the South Pole. It’s almost right at the pole. This crater is about 100 or so kilometers across. It’s very old and degraded. You can see it’s not particularly round anymore, and it’s been beat up pretty bad – that shows its age. It’s probably about three, three and a half, three point eight billion years old. The large ridge, that hill there, M-1 that was the bane of many ground-based observers, is actually part of the outer ejecta ring from the Aechin Basin impact, which is on the other side of the South Pole. So this is a very old, heavily eroded part of the Moon. It is on the Earth side (the Earth would be up in this image, or in the direction of Earth.) Now where we impacted was right next to that little dimple on the upper left hand corner. There’s a little dimple there, a large crater, and we impacted just to the inside of that where it was very, very cold.

But more information specifically on the details can be found at the LCROSS website online at NASA, but also at some of the individual missions who were observing, in particular if you go to the LROC website (that’s LROC: the Lunar Reconnaissance Orbiter Camera - http://lroc.sese.asu.edu/). They’ve got a beautiful mosaic of the South Pole of the Moon at 400-meter resolution, and other instruments are the Lunar Laser Altimeter (LOLA) has beautiful digital elevation maps of the South Pole of the Moon. All of this is public information now, and that’s one of the great things about these NASA missions, is they are required to provide their data to the public. All of the LCROSS data is actually online too if you go to the Planetary Data System and search LCROSS you can find all the LCROSS data, all of our image data and spectral data are located there.

Diane:
You know, Tony, I also saw a really great image on the Astronomy Picture of the Day, in about the last week. It was a wonderful composite. It showed sort of a candy cane stick-up of the pole and the whole Cabeus region in a sort of 3-d projection with the colors: blue for where there’s hydrogen excess and a little bit or a squirrelly line showing where the permanently shadowed region is, and that came out of the science articles that were released, so if people don’t have access to the science articles, then, after they’ve looked at the NASA site, that a wonderful kind of global view. Tony That’s a very nice picture that the LEND team (the Lunar Exploration Neutron Detector Team) put together with LOLA, so it’s an excellent image.

Brian:
So again if you look at the archive section of Astronomy Picture of the Day, you’ll be able to see some of our best imagery so far of the terrain near the South Pole of the Moon.

Linda::
A question here from Owens: Would there have been a better place to land so that we could have seen the flash?

Diane:
I’ll take that, because I’m the astronomer.

Tony:
And you were up there observing it.

Diane: And I was up there observing it -- I led four international teams at some of the biggest telescopes on Mauna Kea. The reason we went to Cabeus was the high hydrogen content that was located by the Lunar Reconnaissance Orbiter, LEND instrument on that spacecraft before we hit. We had the option of pointing in several different regions, up to a few weeks before impact. It was a hard decision; I had many conversations with Tony about “There’s a big mountain in the way,” but it was very important that we went to a place that was hydrogen rich. We had discussed about going to a couple of other regions at about that same latitude, and they would have been easier to see from Earth, but since we haven’t been there, to impact, to really understand what’s there, it’s possible that the richness of what we discovered would not have been so great if we chosen to really push towards Earth based observations. So I think that the plume that we saw and the camera was very diffuse that you saw in the imager earlier in the broadcast, or that you can see on the lcross.arc.nasa.gov <http://lcross.arc.nasa.gov> website. That same image is available. Yes, we could have gone to a bunch of different locations, but we chose a location with the best chance of observing water, and we did see water. And I think that that’s where the ground observers were challenged and yet, I’m really very happy that we went there.

Tony:
And I can add to that, that we got as many eyes on it, different eyes on it, everything from the Hubble Space Telescope, to orbiting satellites (Jen Heldmann was actually the coordinator of all these assets and there were what, 30ish or more. And we had LRO. We had hoped to have Chandrayaan, the Indian spacecraft observing, but it was lost just a month before impact – we were really disappointed, saddened by that. One of the reasons we had so many things looking was because this was an experiment. We’ve never crashed the empty upper stage of a rocket into the Moon at the Southern Pole into the permanently dark crater, and so we did the best we could beforehand to predict what would happen, and as Diane said, we had to go someplace that was relevant to the goals of the mission, and that was a very difficult decision for all of us to make – to pull away from our best Earth-observing assets, because we had lined up such fantastic teams, but if we had impacted where there was no hydrogen, as it turned out, that would have been maybe a nice show for some Earth-based observers, and we might have learned something about impacts and things like that, but it wouldn’t have addressed the principal question, which is: What is that hydrogen? That’s what we had to go after, so that’s why we went deep into a crater. I remember honestly when LCROSS first started, four odd years ago, we were talking about all the various craters on the Moon’s poles to go to, and I said to the team, “We are never going into Cabeus. It’s too big a hole and it’s got a big mountain between it and Earth.” And, in the end, it was the one place that had the most hydrogen, was the most compelling in terms of relevance, and so we had to go there.

Jem:
And there were a couple of detections from ground-based observatories. Kitt Peak Observatory in Arizona and McDonald Observatory observed sodium, so they saw some of the gases that were coming out from the impact.

Tony:
Likewise HST has tentative detection of hydroxyl, as well.

Brian:
So that’s the Hubble Space Telescope.

Diane:
That was very exciting, Jen, because it was really a team effort by many astronomers at many different observatories and you coordinated it all and had us all knowing exactly what was happening as the spacecraft was coming down, and Rosemary Killen who led the Kitt Peak Observations, she was observing at the impact site where many of us were, and didn’t see anything initially, and moved her spectrometer to look just off the limb of the Moon and then discovered a very bright emission. So by being a very good experimentalist, she saw the material that went up, that was hot, that went up really fast. And that was a really great discovery. We’ve known that there’s sodium in the exosphere of the Moon, but to see so much of it released by an impact is very exciting.

Linda::
A question here from Westhill High School: Was the amount of water found expected, and also, are there other locations on the Moon where water can be found?

Tony:
I can take that. The water, as I mentioned earlier, was maybe higher than some would have expected if you assumed a uniform distribution. And others would argue that it’s completely reasonable to have that kind of concentration. One of the things it tells us is that the water is not nice and uniform, but it is probably concentrated in pockets. Some people believed that this was the case. Other people thought it would be much more uniform. So, I wouldn’t say that it was unexpected. We went in with kind of an attitude that it was going to help to determine, at least where we impacted, which it was: either uniform or concentrated, but we weren’t particularly surprised.

Diane:
Tony, did you want to say something about the fact that they’re seeing water in areas where there’s sunlight?

Tony:
Well, they’re seeing hydrogen. That’s one of the other interesting discoveries from LRO, is that the neutron spectrometer appears to detect hydrogen enhancement in areas where there is not permanent shadow, but, what we call “temporarily lit regions,” so there’s a permafrost if you get below the top layer of soil (and I just mean 5 or 10 centimeters) the temperatures can be very cold. It’s because the lunar dirt is such a good insulator (it doesn’t conduct heat), and so if it only gets sunlight for a few days out of the day (Earth days) then at ten centimeters down, you’re at minus 200 degrees centigrade, and water can be stable. So there is this potential that in areas that are not permanently shadowed, you can have water just underneath the surface.

Diane:
So are you saying that because the soil is fluffy, there could be ice, excuse me, there could be hydrogen there, and that maybe the soils fluffy because there’s ice there?

Tony:
We don’t know. We don’t know if it’s the same in the sunlight. Where we hit it was 40 degree Kelvin, and the top surface could be very different from where it gets some sunlight. So what we found is, it really gets to the question: Where else could you find water?” Well, we’re thinking now that there could be permafrost below the surface that really extends to a wide area of the Moon that could potentially be holding water ice. We just don’t know. We can’t tell for sure. LCROSS sampled one place so it really begs the question about going back and sampling some other places.

Brian:
There are a lot of favorite moments from a mission like this, but one of my favorite moments I remember in a news interview before the impact: a reporter asking Tony, “What do you expect?” And Tony’s answer was: “I expect to be surprised.” That’s kind of one of the beauties of carrying out an experiment like this, because if what you find is exactly what you thought you were going to find, you haven’t necessarily learned a whole lot. But then, when things come out that surprise you, that’s a really excellent opportunity to do some learning.

Tony:
We went to a completely uncharted place, part of the Moon we’d never been before, can’t see, haven’t explored. It was really terra incognita, both the impact, the place, everything. That’s why we looked at it in so many different ways, and we tried to keep our eyes wide opened because we knew that if we thought we knew just exactly what was going to happen we’d probably be wrong and miss something. So we tried to come in as open to any possibility as possible.

Linda::
We have a couple more here on the Moon. Since we feel now that the Moon was probably part of Earth at one time, is it possible that the water being found on the Moon now was actually from the Earth at the time of impact or breaking off from the Earth?

Tony:
That’s a good question.

Jen to Diane:
You had comments on that.

Diane:
Well, I think Tony was saying that it’s a part per million; tens of parts per million, so that’s less than a tenth or a hundredth of percent of water has been found in the rocks; tiny vesicles vacuum with water inside of them in the samples that were brought back by the astronauts. And these were reported in the 1970s, and had brought some skepticism to the origin. But since we now see OH (that’s a part or water we talked about before), the OH in the rocks, more of this has been discussed about how volcanism on the Moon could have brought some of the water in the rocks that originated from Earth when the Moon was ripped off by a big impact and formed from mantle material of the Earth, that that water could actually be part of the rocks. But it’s such a low concentration; you can’t really say that that water in the rocks is the water that we saw in the LCROSS, because the reservoirs just don’t add up. You have 600 times the amount, if my math is correct, 600 times the amount of concentration that we saw in LCROSS versus what is known to be in rocks due to the material that was there originally from its formation.

Brian:
So we’re talking about different sources of water. We’re talking about water inside the Moon, incorporated into the rocks that might have come from that early separation of the Earth and the Moon. But then we’ve got these big concentrations of water ice at the poles that probably came from somewhere entirely different.

Tony:
That’s right.

Diane:
That’s right and your point again that we said it was water ice; we actually saw ice particles, and those ice particles have to be fairly pure to have lasted for four minutes. If you mix ice with dirt, the sunlight is absorbed more easily, warms up the particle, and that ice turns into water vapor. So the fact that there’s ice particles, that’s very different than water being in the rock.

Brian:
The Moon has a very complicated story to tell, and water on the Moon seems to be coming from: maybe some of it came from early stages when it separated from the Earth, but a lot of it is coming from comets,

Diane:
…and water rich asteroids…

Brian:
…and maybe even the solar wind, the hydrogen streaming from the sun. So the Moon’s a complicated place. It has a much more dynamically interesting story to tell than perhaps we had thought.

Tony:
One point along those lines is: What I’ve really been inspired by in the last number of years is where we are discovering water, active water systems, and these kind of chemistries that we’re talked about on the Moon, Enceladus in Saturn; we see geysers coming from its South Pole. The entire E ring of Saturn is made of water ice crystals coming out of the moon Enceladus. That’s incredible! It’s probably, in my mind, the greatest discovery in the last ten years, or fifty years. A few weeks ago when we were at a scientific meeting, and they were showing the composition or some of the other things they were seeing in that ice, it looked a lot like the ice stuff that we saw on LCROSS. And now at Mercury, we have a spacecraft getting to Mercury, the Messenger spacecraft, they’ve been finding some interesting things at Mercury. It’s long been speculated that the poles of Mercury have, in their craters, just like the Moon, water ice. We suspect this from radar. So we’re seeing this trend, this thread that ties the entire solar system together, and it’s what we’re finding in these dark craters of the Moon.

Linda::
I have several questions that have come in relating to the saying, “Where there is water there is life.” When searching for water, are we also looking for organisms or life?

Tony:
I know that Jen has thought about this.

Jem:
Well, one thing to keep in mind is that these places near the pole of the Moon that we’re talking about…since we’ve told you that you don’t get direct sunlight there, they’re extremely cold: near absolute zero, 40 Kelvin – that’s really, really cold. That’s too cold for any life, as we know it, and life as we know it on Earth, requires liquid water. We’re not talking about liquid water near the poles of the Moon, because it’s too cold. It’s frozen, so we’re talking about very, very cold frozen water. So it’s very difficult: we’re not looking for life right now near the poles of the Moon. It’s just too cold, there’s not liquid water. But like Diane was talking about, there’s some chemistry going on there that’s very, very interesting that can be creating the types of molecules that are precursors to life.

Diane:
So what’s so important about liquid water for life?

Jem:
We know that all life forms on Earth require it. We haven’t found any form of life, anywhere on Earth that doesn’t need some liquid water. Some need very small amounts of liquid water, but they have to have liquid water, and it’s just too cold by the poles of the Moon to have it.

Diane:
So water is either solid or vapor on the Moon in the poles.

Jem:
Right

Linda::
My favorite question is always: “Do you like your job as a scientist, and what can a sixth grade student do now to prepare for a life in aerospace and science engineering?

Jem:
I think it’s safe to say that we all like our jobs.

Tony:
Mostly.

Jem:
It’s pretty fun. We get the chance to answer really interesting science questions. We get to explore places. I mean, our job is to explore the Moon. How cool is that! So that’s pretty fun. For starting in sixth grade, one thing you can do is come to Webcasts like this. That’s great so you can learn more about: What is NASA doing? What are other countries doing? What are we learning about space? What do we know about the planets? And I would say, going to your local science museums, going to the planetarium, going to astronomy star parties, if you’re interested in that, reading books from the library, all sorts of things like that. Do you guys have other suggestions?

Diane:
We all know that math and physics will become part of your daily tools when you’re a scientist, and I love my job. But I think it’s also very important to develop tools of critical thinking. So that it’s not just the knowledge, but it’s how we think. It’s how we think as a team. It was together that we came up with these ideas about what must be happening on the poles of the Moon, by brainstorming. Just keep in mind that it’s important to always bring your attention to everything that you do and see.

Tony:
I know we’re short on time, but just to emphasize those two point that I think are really important is that teamwork, that getting involved with groups, doing the kinds of things that we do in groups is what makes a great scientist and a great engineer. Nobody does this alone. It takes a huge team effort, and that’s important: Get involved in groups.

Brian:
Well, I think that that probably a good note to end on there. I will point out that what has happened here is: It looks like we’ve gained an entirely new view of the Moon. The Moon is something very different than we thought it to be. But in answering some of these initial questions from LCROSS, it sounds like what you’ve done is raised a large number of new questions. So what that means is, there is a vast new area of exploration that is going to be available to our next generation of explorers. We have a team here that is doing some amazing work, but they are raising new questions that we’re going to need a new generation of people to answer, and we’re looking forward to seeing the answers that you, the next generation of explorers, come up with.

I want to thank our team of scientists here who’ve done such a wonderful job of the LCROSS mission. Again: Tony Colaprete, Diane Wooden, and Jennifer Heldmann. Thank you all, and thank you for joining us.

 

 FirstGov  NASA


Editor: Brian Day
NASA Official: Daniel Andrews
Last Updated: October 2010