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Dr. Anthony Colaprete Lectures on LCROSS
"Prospecting for Water on the Moon: The Upcoming LCROSS Mission"
Good evening, everyone. My name is Andrew Fraknoi. I'm the astronomy instructor here at Foothill College, and it's my pleasure to welcome everyone in the auditorium and all those of you listening or watching on the web to the first 2009 Silicon Valley Astronomy Lecture Series.
This is a program sponsored by NASA Ames Research Center, the Foothill College Astronomy Program, the Astronomical Society of the Pacific, and the SETE Institute, to bring new ideas and new discovery in astronomy to a wider public.
This evening we're very pleased to welcome a speaker who is going to talk to us about crashing on the moon...on purpose.
Our speaker is Dr. Anthony Colaprete, a planetary scientist at NASA Ames, and the principal investigator for the LCROSS mission.
He received both his undergraduate and graduate degrees from the University of Colorado, and worked on a number of sounding rocket, space shuttle and small satellite projects before graduating to crashing the moon, because that's what LCROSS is going to do.
His research specialties include the climates and clouds of other planets, particularly Mars, and impacts in the clouds of dust that they generate.
And you'll see how important impacts will be in the discussion of the mission that he's the scientific leader of.
At Ames, he's also the leader in the development of future instruments for exploring Mars and the moon. So, ladies and gentlemen, here to tell us about this unique experiment of crashing into the moon on purpose, it's my pleasure to introduce Dr. Anthony Colaprete.
Thank you. It's great to be here tonight. I'm a first time visitor. But hopefully that will change. This looks like a really great series. And just by the show of repeats, it says a lot about how great it really is.
I will try to stay near the podium, I've been told, but I do tend to wander a bit. So we'll see how this goes. I'm also going to turn off my wireless to save my battery here. It would be a shame if we quit halfway through.
I'm the principal investigator for LCROSS, as was mentioned. I'm also the payload manager, which we'll get into later, but I've frequently had fights with myself. We want more science, you can't afford it. We want more, can't afford it. But as you'll see in a minute, LCROSS is actually a very unique mission in a lot of ways, but it's also a unique mission for NASA. It represents a different flavor of mission than NASA typically does.
And you'll see how that is a little bit later in the presentation. Now I want to talk about first what LCROSS is about, what is it trying to do, what is its motivation, why are we doing it, a little bit about the expectations, what we'll learn, that sort of thing, and then jump into the actual project itself.
LCROSS was really motivated about 10 years ago by another NASA Ames mission called Lunar Prospector. Lunar Prospector was another low cost mission. It was one of the very first, if not the first discovery class missions that NASA flew, it was so simple it didn't even have a computer on board. But it studied the moon. In particular it had an instrument that studied neutrons. These neutrons emitted from the soil of the moon are absorbed by a variety of elements, including hydrogen.
Now, one of the things that it discovered was hydrogen was in abundance in excess near the poles of the moon. I have this little figure here from Bill Ferrell's original paper. What this just shows is the amount of neutrons measured. Where it's bright, there's more neutrons; where it's dark, there's fewer neutrons.
So what that means, you interpret that as, there's less hydrogen here and more hydrogen here. And it was interesting that the hydrogen was in excess at the poles. People immediately thought what's unique about the poles on the moon. Ah, it might be colder there. So maybe there's some volatility related to the increase of these hydrogen atoms at the poles of the moon.
Now, that was the thing. The instrument on Lunar Prospector could only measure hydrogen. It couldn't tell you what form it was in. So we don't know that it's water. So that's one of the principal questions that's remained ever since and been heavily debated since Lunar Prospector discovered this 10 years ago is what's the form in the hydrogen.
That's what LCROSS is all about, it's trying to understand what is the form of this hydrogen, what's its distribution and where is it located. So that's kind of what I've written out here, is the debate over the form and concentration of this hydrogen has really been raging, and I'll get into this later. Some extreme camps have been established. It's this way. It's this way.
And that's usually the case when there's very little data. This is about all the data that we have right now. So LCROSS and future missions will really add to this.
So adding to this, then, got some kind of motherhood statements that you usually see in a project presentation. And I had to include them here. So this is the LCROSS mission rationale listed out here. It's what I just said. We want to understand what this hydrogen is. We want to know quantity form and distribution. We want to use these measurements as ground truths for the other measurements that will be made by the lunar reconnaissance orbiter. LRO, Lunar Reconnaissance Orbiter, is the spacecraft we're hitching a ride to the moon. It has a neutron measuring instrument on it as well that will make better measurements. We want to provide a ground truth, meaning we'll sample the dirt you're measuring and then so you can tie the two together, kind of calibrate your measurements.
One of the interesting parts about LCROSS and LRO, for that matter, is these are ESMD missions. What does ESMD mean? It's a particular division within NASA. There's a science mission directorate. This is the explorations systems missions directorate. The exploration systems is the directorate or vision within NASA that's building the Aries rocket, the Orion capsule. They're the directorate that's responsible for bringing humans back to the moon.
So they are the ones who are sponsoring these missions as exploration tools, robotic precursors, to understand what it is, where we're going and where we need to go and consider.
LROs, as you'll see later, will map the moon at unprecedented detail, providing the kind of information to do highly precise landings on the moon in more hazardous places than we went to with Apollo.
LCROSS actually provides a bit of information that will be decisive. We're very interested in the poles for a lot of reasons. One of the reasons is water. It could be a valuable resource.
So moving on past this, then. There are a lot of science mission objectives associated with this mission as well. So we have the support of the science mission directorate within NASA, and we're working very closely with them. And I've listed some of the basic questions here.
Fundamentally, we're going someplace we've never been before. We've never been to the poles of the moon. We've always all the other landers on the moon have landed near the equator in the tropics. We've never been to the poles with a lander.
We've never explored inside one of these craters that has never seen the light of day. The floors of some of these craters have not seen the light of day for maybe two, three billion years. So we really are going someplace unique never before seen.
So a lot of the basic questions we understand about the moon like what's the dirt made out of we're asking again, is it made the same here at the poles where things could be very different.
So we want to ask these questions. So we are really going to look at this is the primary objective: What is that hydrogen that we see? But also what's the regular, the moon dirt made of? What's its strength, depth, grain size, composition. Is it even similar to Apollo sites. That will help us decide whether we need to do follow on missions to explore it some more.
One of the aspects I'm very interested in is the lunar atmosphere. Usually you hear there's no atmosphere. You could argue it's an exosphere, not an atmosphere. But there is and there are volatile processes that occur on the moon. And it's these volatile processes that are potentially responsible for that hydrogen.
So we're very interested in how that lunar atmosphere respond to our impact. You'll hear in a minute how did the water get there? It could have been from impacts from astroids or comets. We're in a sense mimicking one of those impacts. We get to study that process and understand it a little bitbetter. What are the time scales for it to recover, and how do these volatiles, like water or dust, migrate around the moon. These are just basic fundamental planetary questions that apply to any body without an atmosphere in the solar system, which are quite a few, and also have fundamental bearings on the delivery of volatiles to earth in the inner solar system. So there's a lot of very exciting, interesting aspects to this mission.
So some of you probably know this, but some of you might not. And I think it's really kind of a cool characteristic of the lunar poles of the moon. How do you get a permanently shadowed crater? And that's how you actually get the water at the moon.
So I phrase it here: How could you get water at the poles? Well, if you don't have an atmosphere, it volatiles, it evaporates off or sublimes off very quickly.
Well, in some of these dark craters, this is an image of the south pole of the moon from Clementine. These craters that are right near the pole, the south pool is actually about right about where this red dot is, on Shackleton crater. This is Shackleton. And the sun is very low on the horizon at the poles all the time. The moon doesn't have a lot of tilt to it, so the sun never gets by the horizon by more than a degree or two.
This little cartoon here, you can see that the sun may never actually get to the bottom of this crater, even as it goes around in a circle around this crater. And first test of a video here, we'll see if it works.
An excellent example of this is this beautiful animation made from new selenoid data, cargo data from a Japanese satellite, showing the allometry of the moon and then a model to represent the lighting. And you can pick a particular spot on the moon. For example, inside this crater here, right where I'm pointing, and you can see the black represents shadow. There are parts within these craters that no matter where the sun is, during a lunar day, you never get sunshine down there.
And without an atmosphere to transfer heat from one place to another, if you don't have sunshine, you get cold.
So in one of these really dark craters that never gets sunshine, you can get exceedingly cold. You can get down to minus 200 degrees below zero centigrade.
The permanently shadowed craters on the moon are among the coldest places in the entire solar system, which is kind of a fascinating fact. So LCROSS will be the first thing to land hard in one of these permanently shadowed craters, and bring the material up into sunlight so we can study it. And that's the only way we can study it without much more extensive capabilities.
So why do we want to do this from an exploration standpoint? Water is expensive to haul to the moon. So if I'm interested in bringing water to the moon, something about this big, depends on how you do the math, it's going to cost you $50,000 at a minimum. So I've drank about $25,000 worth of water here. Talking with some of the guys in Houston, who are in charge of the astronauts, one of them, in particular, told me there's no way in a great Houston drawl, there's no way I'm going to have my astronauts drink moon water. I'm not going to have them suck the water out of the dirt; we're going to bring the water. But, he said, we're really interested in not bringing our fuel to return home, our fuel to go to Mars or fuel to go somewhere else. Every time we launch a shuttle it's a couple million pounds of hydrogen and oxygen. That's a lot of fuel if you want to bring it to the moon.
So we're very interested in extracting hydrogen and oxygen from the moon, the basic parts of water, and using that to actually make rocket fuel. Actually doing this on the moon, too, proves to us that we can do it on Mars, which is one of the fundamental mission architectures for a human venture to Mars, is the insitu to produce your fuel for the return home. Much rather try that first when you're two and a half days away from earth than two years away from earth. So what this plot shows is how the poles could help you.
There's hydrogen and oxygen all over the moon. It's locked up in the minerals of the dirt at various concentrations. And at the equator, for example, there's about 100 parts per million of hydrogen in the lunar dirt. You can extract that by heating it up and driving off that hydrogen.
At the pole, if there's 1% water ice, we think there's about 1% water ice in some of these permanently shadowed craters, that would explain the hydrogen we see.
This is the energy in kilowatts per kilogram. So how much heat you've got to put in to get the hydrogen out. To get it out of the dirt you've got to get it real hot. You need to have about 2200 kilowatt hours to get the dirt out; whereas, if it's water ice, you know how easy it is to boil water or melt ice and extract a hydrogen from it. So while it might be easier to go to the equator and dig up dirt as opposed to going to a minus 200 degree shadowed crater to dig up dirt, when you actually work out the cost production ratios, it's easily five to 10 times more efficient to dig up ice out of the poles than it is to extract dirt.
Those are some estimates, some studies. So the fundamental position going in or question we want answered is, hey, do we really have this kind of ice at the poles? Is it worth exploring this further? Or should we just say, no, we're going to settle and going to the equator or sticking to Apollo like landing sites in the future.
So we're really interested in understanding the water at the poles for what's called insitu resource utilization. It's a buzzword you'll hear a lot. If it's above 1% or so, then it makes polar mining very efficient.
So that's the exploration side of the equation here. That's why the ESMD, the Exploration Systems Mission Directorate, commissioned the LCROSS mission.
So what do we know about the polar hydrogen? Here are some pretty colorful figures of the south pole. Here's some craters. If you remember, I was pointing to that Shackleton crater, the dark crater with the pole right there. This is it.
What's shown here is the white areas are calculated shadowed regions. So these are these permanently shadowed regions, cleverly shadowed like snow. And the colors show where we see the hydrogen maps. Or the hydrogen from the Lunar Prospector mission.
The Lunar Prospector instrument had a very big footprint, big view. We're not exactly sure where the hydrogen is, about 70 kilometers or so across depending on its altitude at any particular time. You can see the distribution of blue, the blue means high hydrogen concentrations. It's kind of just smeared everywhere.
So we really don't know where, if it's here or here or where. The theory is if it's indeed volatile and associated with cold places, it's stuck in these cold traps. And these cold permanently shadowed regions are trapping this volatile. So a number of experts have deconvolved the data. They say, okay, if it's actually inside these cold traps, we can do some very clever processing techniques and kind of stuff it back in. And it's oversimplifying a very complicated process.
But when you do that, here's a map that Rick Elfick, who is also at NASA Ames, generated showing the percent water, water equivalent hydrogen, percent of water in these permanently shadowed regions. Here's Shackleton. It's about a half a percent. Here's Fostena, a little bit less than half and so on.
So these are kind of the water percentages we're interested in. You can see, just from this map, though, still we don't have the resolution or the understanding to understand what's going on within this crater. This is a pretty big crater. This is about 35 kilometers across. It's big. So where in that crater is the hydrogen? Is it everywhere in that crater? Smooth? Why is this crater so much wetter, if it is indeed water, than this crater and that crater? Why is this so high? These are fundamental questions that indicate something about the process or the retention or the history of these regions that we just don't understand at this point.
So there's a fundamental question that we have to address: Is it uniform? Or heterogeneous? From one query to another. And how is it at smaller scales? Obviously it differs on these big scales from 50 to 100 kilometers, but what about different smaller scales. This is really critical. This is what I'll get into in the next few slides.
So at the smaller scales what we're really interested in is it smooth. So is it evenly distributed at low concentrations. So you can imagine, this auditorium as a crater. And you measured from space on average across the auditorium 1% water. Now, you could create that measurement in a couple different ways. One, you have 1% water evenly distributed across the entire auditorium. Just a thin frost. Or you could have a glass of ice cubes right in the middle or in the corner. If all you see is your view is just the auditorium, you can have a high concentration, look exactly the same as a very uniform field.
That's the problem. There are fundamental processes that are affecting those two possible solutions and members.
So I call that these low concentrations, nice and uniform. The smooth approach, our smooth representation.
And somehow within the project we got to start talking about peanut butter. That's the smooth peanut butter. I don't know how, but it stuck. Here's another peanut butter pun. But I didn't mean that actually.
Another is chunky. Patches of ice. I think originally it was said raisins and pudding to me, and then we got into peanut butter. We were hungry that day or something. Chunky is you have a big block of ice over here and everywhere else it's dry. That would make the same measurement that we've seen from Lunar Prospector. That, of course, is chunky peanut butter.
That's really what LCROSS is all about. Or one of the things. First, is it water? That's a fundamental question we have to answer. And then is it smooth or chunky? That's critical to understanding from the scientific standpoint, the processes, the distribution, how it came to be, but also about mining.
Do I have to go find the one ice block in the middle of this 20 kilometer crater, or do I just get to scoop it up just about anywhere I like to go? That's really important. So craters. They're important. They're important across the solar system. You should all have great respect for craters. They are the dominant surfacing erosional process across the solar system. They occur today. And they're very important to the question that I just brought up.
A point I like to make always is that there are about two to three LCROSS size impacts occurring on the moon now per month. We observe them by impact flashes. You can observe them with a 10 inch telescope and high speed video pretty easily.
The neat thing about LCROSS is we know exactly when and where this impact is going to occur. The impact crater that LCROSS is going to make is about 20 to 30 meters. It's about the size of the East Crater. This is the Apollo 11 landing site. Here's the landing module here. This is East Crater. They flew right over this on their way to here. This is about a 10 meter or so crater.
These are important craters in the scheme of things when it comes down to hydrogen, because of their excavation depth. And an important thing to know about the Lunar Prospector hydrogen measurements is they can only penetrate the sense to about a meter, about 77 meters or 100 centimeters or so into the lunar dirt. They're really only seeing the top meter of lunar dirt. We know the hydrogen concentration is in the top meter, and we don't know what's going on below that.
These craters, a 10 meter crater, like this guy, excavates, rule of thumb, about a meter deep. These kinds of craters are affecting what we see from Lunar Prospector. And that's very important.
This shows kind of the distribution of these. This is a 30 meter crater here, the distribution of these craters. There's so many of these size craters per area on the moon.
And this is important to determining whether or not you have smooth or chunky peanut butter I mean water. Here's a little schematic I've drawn of the depth. This is the depth in the dirt and this is some kind of horizontal distance across the lunar surface.
So you have these craters with five meter diameters that excavate to about half a meter deep. The rule of thumb is, if you really want to know, crater depth is about a tenth its diameter.
These happen about every one million years per square kilometer. If I stood around on the moon for a million years within a kilometer of me or so, you would see an impact that would create a five meter crater.
A 10 meter crater, which excavates down to about a meter deep, the depth at which we sensed with Lunar Prospector, happens about every 15 million years. That's a pretty long time, actually. And the kinds of processes that we think that bring the hydrogen, if it's water, into equilibrium, mainly diffusion and thermal gradients and things like that, have shorter time scales than this.
So between these craters we think things should be uniform. So when this crater hits, however, this impact hits and makes this crater, it disrupts everything. It throws out ejecta. Buries some. Excavates some, heats up. It's volatile. Sublimes some water. Some of that escapes. It makes a mess of things. So you can actually kind of quantify exactly how disrupted that top meter should be if you had a perfectly uniform frost, how disrupted it should be. And when you do the math, for a 10 meter crater, it's rather simple math here, crater diameter squared divided by the crater spacing, meaning the distance between a 10 meter crater, which is about 100 meters or so on the moon. And you get about 99 percent is undisrupted. So that's quite a large number.
That means, if the peanut butter is smooth, 99 percent of the area should have about 1% water content. That's what the hydrogen measurement is.
So that predicts a smooth peanut butter, or water. Now, if it's chunky, yeah, there's one large commentary impact, for example, which happens much less frequently than astroid impacts. But it delivered a big chunk of ice, or a large concentration of ice, enough to result in the observations Lunar Prospector made, and it may never get disrupted in the last billion years because you need just the right kind of impacts to disrupt it and distribute it evenly, so on and so forth. So the two end members are testable in this scenario.
If LCROSS hits and sees nothing at its detection level, and its detection level is below half a percent of water, then we would say, well, we don't have evenly chances are really good, better than 99 percent, that we don't have uniform water everywhere. It is actually heterogeneous. And that's really important.
So we've immediately confirmed or favored one model over another. And then we can think ahead about what we do next. If we do see water at the half percent or better, then that says actually it is uniform.
So we aren't talking about chunks of ice everywhere. We're talking about a uniform smooth layer. If we actually get lucky and hit a chunk of ice and we see 5% water, 2%, 3% water, then that says yes that's the same as not seeing water. It's heterogeneously distributed.
So that's one of the principal results or contributions LCROSS will make. And that will hopefully settle some of the debate we've had for the last 10 years over what is producing this hydrogen signal.
A little bit now about the LCROSS mission. The LCROSS mission is really a mission of opportunity. It's one of the several times I've been impressed with NASA's wisdom, one of the few times. And there are a few. LRO needed a larger launch vehicle. It was going to go on a Delta 2. And its mass grew. So they needed a larger launch vehicle. Unfortunately, there's no Delta 2 plus. So they had to go to an Atlas. And Atlas carries a lot more weight, a lot more mass to the moon.
Suddenly, NASA had an extra 1,000 kilograms of lift capacity to the moon with LRO. LRO had already been working on their project for two years at this point. But NASA says: Let's go and see what people can do. So they put out a call to all the centers and said: What can you guys think of? And at NASA Ames we formed a quick group called Blue Ice. Really looked at this. We submitted six proposals out of Ames. 19 in total were submitted to NASA. Down selected to four. We were selected. All that occurred in a span of about four to five months. We knew we had to hurry. And, oh, by the way, you only have $80 million to do it. So our budget is actually 79 million. And you had to get it done in about two and a half years.
So that's how LCROSS was born, was: You have a thousand kilograms of the moon, what can you do with it? There were orbiters. There were several other impacter ideas, so on and so forth.
The unique thing about LCROSS that tipped the scales for us, and there's two things actually. One is we didn't use that thousand kilogram extra allotment for our impacter. We used that for what we call the shepherding spacecraft. This little bit here you see on the end. I'll describe it a little bit more in a minute.
What we used as our impacter was the space junk that they would otherwise throw away. This 2300 kilogram centaur booster that pushes ourselves and LRO to the moon. In a way, we cheated. We got more than 3,000 kilograms out of the deal for the cost of 1,000 kilograms.
We also then got then a very unique observing position. We got the best seats in the house for observing the impact. That's how we're very different from Deep Impact.
Our mission is frequently compared to Deep Impact. And a lot of our science team members are Deep Impact science team members. But Deep Impact was never closer than a thousand kilometers from the impact.
We're never farther than 600 kilometers from the impact. We actually fly through the ejecta plume before becoming an impact ourselves.
There's essentially four stages, I can show you a movie on this real quick, for the LCROSS mission. There's the launch, where we launch stacked LRO, lunar reconnaissance orbiters on top of us. We're underneath. Here's the big centaur motor that pushes us to the moon. LRO detaches, goes on its way to the moon, starts its commissioning and mapping phases. And we go on a three to four month cruise around the earth. Doesn't say, but it got cut off, earth.
It's really hard to see here. Here's the ecliptic plane. We do a swing by the moon and get into a highly ecliptic orbit around the earth. Very large, 700,000 kilometers at times. And we do that to get position to impact either pole of the moon. So we get into an orbit that times things just right so the moon comes around and we run into it. And we can go swing by the south or swing by the north depending on which pole we want to hit. A very clever way to do this at very low fuel costs.
So we do that for three to four months. We have a few calibration events in there, so on and so forth, but it's pretty boring. But then it all comes down to the last nine hours. At nine hours from the moon we separate from the centaur. We target it on its way. We separate this part of this spacecraft from the centaur. The instruments turn and look at it, as it heads into the moon. And then we generate a four minute separation between us, meaning we're four minutes behind the centaur going in. It impacts. We take four minutes worth of data. We're actually on for an hour, but there's four minutes of useful real critical data, and then we impact ourselves.
I can show a movie, but I don't think it adds much more than what I just described.
Prospecting with six and a half billion joules. That's what the LCROSS impact is. And that's what makes it unique. We have relatively slow speeds hitting the moon, compared to Deep Impact. Deep Impact had a closing speed that was in excess of 10 kilometers a second into Temple 1. We have much slower impact velocities, because we're just going to the moon. It's about two and a half kilometers per second. But we have a lot more mass. Like I mentioned, we have about 2300 kilograms worth of mass. So when you do the math, that works out to over six and a half billion joules of energy.
It's all about the impact. Very early on we had a large team of varying impact specialists. They all have their opinions and their different methods for calculating what to see. But that's what we would see, but that was critical. We did a lot of very sophisticated analytical modeling. This is called smooth particle hydrodynamic modeling, where they simulate each grain of dirt. We had some running on super computers with over 11 million grains of particles of dirt that are a few centimeters in size. And the simulations last all about five seconds. Meaning we can only simulate the first five seconds of the impact. That's essentially the crater formation time. And then we do different codes to calculate the ballistic trajectories out from that.
We also do really cool gunshots at Ames, using the vertical gun.
There's a large vertical gun that's actually Apollo vintage that's been maintained. And I'll show a neat video. Pete Schultz, who many of you probably have heard of, has been using this gun for years and years to actually study impacts.
And he's one of our team members. And this shows an impact from looking above in the vertical gun the way LCROSS will see it. What we did, we simulated the permanently shadowed crater rim, the impact angle of about 60 degrees, our impact angle. It's going to be better than 65 from the horizontal. And the position of the spacecraft.
So the sun's coming in from the side. I'll play it again. What you see is the flash, that first area right there. You saw the flash. We'll see that. You'll see a high velocity vapor plume come up the middle. It's very unique to low velocity impact. Some new impact signs Pete's been doing. And you see the ejecta start to come out. We call that the sunrise. You can't see the crater floor. You can just maybe see it. That's light from scattered light coming off the particles, and then the ejecta continues to come out in a spectacular form way for several minutes. In the real world, it will last several minutes.
We've done all kinds of work to try to understand this impact. And, again, this impact is going to be quite unique. How is it different from other lunar impacts? Some of you may know we've impacted the moon quite a bit. Our first missions to the moon were just hit the moon, the Ranger missions, and we finally got right, I think, on Ranger 4, we finally hit it.
We've also impacted it more recently. Lunar Prospector, the mission that discovered the hydrogen, you run out of fuel. You're in orbit around the moon. There's only one place you're going to end up is the moon. Lunar Prospector said let's try an experiment, the same kind of experiment we're talking about with LCROSS. They impacted inside of Shoemaker Crater, one of these permanently shadowed craters. But it was a very small spacecraft, about 150 kilograms. And it came in, because it was in a low orbit around the moon, comes in at a grazing angle. Very low angle.
What this diagram here shows is a total mass of ejecta, stuff coming up as a function of the impact angle for a couple of different impacts. So here's Lunar Prospector way down here, this little dot. Because it's coming in at a grazing angle, such low mass, it hardly would have thrown up any mass at all. Nothing was seen. A few telescopes tried to observe it from the ground on earth but nothing was seen.
Smart 1 impacted almost a year and a half ago, I think, now, was a European mission to the moon, it was a technology demonstration mission. It too ran out of fuel. They brought it in about 20 degrees south of the equator, not at the poles. But it was comparable to Lunar Prospector.
It was a couple hundred by 240 kilograms, a little bit heavier. But it was also coming in at grazing angle, coming in at three or four degrees. They were actually worried they were going to clip a mountain. That's exactly what we think did, they clipped a mountain before hitting the surface. So we made predictions with them. And we actually had observatories in Hawaii observing it practicing for LCROSS. It could either be down here, or, if it hit a hillside impact on models, predicted it could be around here.
The Canadian/French/Hawaii telescope actually did observe the flash and they did observe ejecta dust being lifted up into sunlight. And there are papers coming out on that soon.
So this was proof of concept that with the new telescopes that have been commissioned in the last 10 years or so, with very fantastic detectors, you can even see a very small impact like this. Not just the flash of the impact, but actually the dust coming up and being illuminated by sunlight.
Now, LCROSS is way up here. It's, again, we come in at a very steep angle. We have 2300 kilograms. So we're throwing up a lot more mass. Our shepherding spacecraft, when it impacts, it's about 700, 720 kilograms. Starts out near 1000. But it burns a lot of fuel just getting to the moon.
We actually have two very respectable ejecta clouds. You saw the impact video from looking above. That's how we'll see it on our shepherding spacecraft. But from the side it will look like this.
This actually shows the height above this. This is a south pole. So that's why it's going down. This shows a heightened kilometer. 1740, 1760. So it's a radius.
This height right here represents about 20 kilometers above the lunar surface. What this shows is a density of particles. I didn't put the scale on here on purpose. It will be just too confusing. The point I want to make most of the ejecta is going to be constrained in the lowest five or 10 kilometers above the surface. Some material does get very high. It has high velocity component to it. Not as much as Deep Impact would, for example, because we're slower impact, but some. It lasts, this is 95 seconds later. Our predictions say this ejecta will finally fall out and settle out in about three minutes' time. But you can actually, I'll comment about how bright that is from earth.
It should be bright enough to observe with a 10 or 12 inch telescope on a clear night. So where are we impacting? This has been very difficult. Hey, it's a crater. You find a crater, you impact.
Well, it's hard because we don't dictate when we launch. LRO does. We have to be prepared for any possible launch they have on their books. That said, we want to also make sure that there's a ground base component that can observe the impact. So it has to impact at a certain time and place.
We need to impact such that there's the maximum amount of sunlight above the crater, so that the ejecta comes up, the sooner it sees sunlight, the sooner we get information. So we have to consider that.
We have to also consider the target properties. So we're trying to make an impact ejecta thrown up in the sunlight, not good if you hit a slope this way because the ejecta goes out sideways. And, likewise, we want to hit something nice, fluffy, like flour, as opposed to gravel or rocks. If we impact into gravel or rocks, our energy, the six and a half billion joules, goes into crunching rocks rather than throwing it up into space. You can do this experiment at home with your kids. Get a sack of flour, pour some in a pot. Get a sack of beans. Pour that in a pot. Have your kids hit it and see which makes the bigger mess.
It's exactly the same thing we're worried about here. We want the bigger mess. We want the flour to go out.
So we have to consider all these things. As I mentioned, the LCROSS crater is only going to be about 20 or 30 meters across. So we are worrying at a scale that we have very little data on for the moon. LRO will finally provide this data. Actually, the Japanese mission is providing this data now. And the PI for the terrain camera is actually coming out to Ames in a few weeks to visit with me to talk about this sort of thing.
So we only now finally have the kind of data we need to really understand where we're going. The problem is, of course, we're going into a dark crater. So you can't see down there. So imaging doesn't really help you. The Japanese have demonstrated that you can actually, by adding a bunch of images together, see the bottom of these shadow craters, things to light reflecting, scattering off the walls of the crater.
So we really have the technology now and the missions and the data now to actually support this mission in a proper way.
And, of course, there has to be some hint of hydrogen there, too. So when you throw all these things together, you actually you run out of actually sites that you can impact. So this is the north pole. These are candidate north pole craters. We examine several just to get a flavor. We have a targeting accuracy of about a kilometer. We'll be able to hit to within a kilometer, three sigma. The navigation team wouldn't let me take advantage of that full capability. They started to sweat too much when I started showing them smaller and smaller craters.
So we have a rule that I can target a three and a half kilometer area. And so the craters we're looking at now for our April launch dates are crater this region, this white area here represents shadowed regions, permanently shadowed regions within this crater. This is a radar data set, by the way, made by the earth. So actually we can illuminate certain parts of these shadowed craters with radar. Very helpful. So we're looking at Crater A and Crater F. A lot of these other craters, either the illumination isn't good or the surface isn't good. For example, Crater C was thrown out, thanks to the Japanese data that showed that slopes were just too steep. So we're avoiding it.
E is on the far side. So this is the far side of the moon from here down. Can't see it from earth. So when you kind of throw all this together, you end up with this little slice, just a couple craters that you really want to focus in on. So those are craters we're planning on going to for our upcoming launch.
The spacecraft and payload: As I mentioned at the beginning, the whole project is an experiment within NASA. Can you build to a fixed price? Which is not normally how NASA does missions.
Usually there's a cost bogey. There's a cap you build to. But then there's requirements change. You can go over it. We were told by exploration mission directorate you go over your $79 million and you're dead. We mean it.
And so that, plus we only had two and a half years to put this all together, said that we had to do something innovative compared to how we normally would do missions.
And what we came up with, along with our primary contractor Northrop Grumman, is capability driven products, meaning rather than meet a scientist and the science team saying we need to do A, B and C, let's go do it, those are requirements. And we're going to negotiate a little, but we've got to meet those. That's how a typical NASA mission is frequently done. What that does is it drives very unique systems, very expensive systems, very lengthy development schedules.
What we did is we started from the bottom up and said what capabilities exist. We did this on the spacecraft side. We did this on the payload side. So, for example, on the spacecraft, we couldn't say we're going to build a new spacecraft, what exists out there that we can take advantage of. One was LRO. LRO had been at this two years. We said can we have your spare avionics or build a set like it? That's a good idea. Let's do that, that will save us development time. Then we looked around and we said Northrop Grumman came up with this brilliant idea, what can we build the spacecraft out of. You're putting something between the rocket booster and LRO. LRO's going to be pretty dissatisfied if you put a cheap something in between them and an unproven something.
And proving something costs money. So they had the idea of going with this giant piece of yellow sewer pipe. This is called the ESPA ring. It's an acronym in an acronym, so I won't go into what ESPA stands for. But it's an adapter ring that was designed to bring secondary payloads Atlas missions.
So it's already been designed and tested and qualified to stick between the primary payload and the motor. It's a giant chunk of aluminum. About 150 kilograms. There's no worries. You just you can complain about it, but no one would take you seriously. That made LRO very satisfied that they essentially were mounting straight to something that was meant to be mounted to. And all they had to worry about was the peripheral. The peripheral we could demonstrate was very robust. Also saved us a lot of money. It was built.
So this piece of sewer pipe has these little ports on it. Normally you put a little small spacecraft on each of these ports, little secondary missions. What Northrop Grumman came up with is really ingenious. Made this possible, was they used each of those ports as a little panel, little module that contained various spacecraft parts. The batteries are over here. The computer's over here. The navigation system's over here with the star tracker and so on and so forth. And over here is the payload. This is a large solar panel. So it's modular. All these things just come on and off and so on and so forth. Very accessible. The tank in the middle, that's the fuel tank. That's a leftover tank from a satellite, series of satellites called a Tetris satellites, that was left over in a warehouse. We got it, changed the plumbing a little bit, went with it.
The kind of philosophical overpinning or underpinning was glue it. Don't develop it. Find things that all you have to do is glue them together. And that's what we did.
And what it also allowed was this payload panel to come up to NASA Ames. NASA Ames developed and integrated and tested the entire payload. We went down to Northrop Grumman, got the panel, brought it up to Ames, integrated everything on it, drove it back down there in a FedEx truck, like web service, and stuck it on the spacecraft, plugged it in. And that's how it had to be to make these things work out. This is the spacecraft going into a thermal vacuum chamber. This is a chamber that simulates the space environment at Northrop Grumman. This was in June of last year. So we were ready. Our original launch date was October 28 through the 31st of last year. We were ready actually to be strapped on and go at that launch date. So we met the schedule both under budget and with schedule slack across the board.
So this is the payload. Developed here at Ames. It's in what we call the POD, the payload observation deck. It's this large aluminum housing that acts as an optical bench. Everything's mounted to a single piece of aluminum. If you align that one piece of aluminum, you know everything else is aligned. It's got a lot of instruments in it. That's what's exciting, for this very inexpensive mission, we have nine instruments onboard.
And, again, we used the philosophy of looking at what capabilities existed, rather than say we need an instrument that does this, this and this, we said, well, these are the things we're interested in. What exists that can accomplish those things?
And, for example, our near infrared spectrometers, which is this telescope here, one of the workhorses for looking for water for us. This instrument was developed by a company on the East Coast. The spectrometer was, called Polychromix. The instrument is used in assembly lines for measuring alcohol content in beer.
It's really actually used quite heavily now for recycling carpet. And so it's rugged because they have it on their belt and they actually go up and measure carpet and so on. We essentially talked with them and said: Your instrument measures the kinds of things we're interested in. It's built. Will you work with us to rapidly prototype a flight rugged one? We'll work with you to make it able to go in space. And that's what we did. The instrument providers delivered their instruments from requirements, from the contract signature to when they delivered their flight units in nine months. Incredibly fast and way under, way under budget. So really exciting.
We have ultraviolet spectrometers. We have a visible camera, near infrared cameras, mid infrared cameras and a flash photometer, special radiometer for looking at the flash.
I'm going to play a little video here. I'm running long. I'm about done. This is what we'll see from about 40 minutes out. Starts about 40 minutes out from our visible camera. That's about the field and view aspect ratio of our visible camera, called a context camera. That little yellow circle is the field of view of our near infrared and visible spectrometers. And this is us flying into the moon, not at real speed. From the time it starts to impact is 40 minutes.
But what you can see is it's going to be heck of a ride. We will be streaming the video from the cameras real time via the net, and so this is another aspect of the mission that I was really keen on making happen, was making this a real time event to experience for everyone to experience with us. It's not I was so impressed with Deep Impact. Ground observers saw the impact before NASA saw the impact on Deep Impact.
And that's really important for generating the excitement, the interest. Also, I am now on a couple of Apollo hoax websites as someone who is propagating the hoax. I think it will be hard if we stream the video and see the impact simultaneously for us to really pull that off. So in a hoax like fashion. So hopefully this will convince everybody that it really happened, seeing the video the same time you see the flash up in the heavens.
So we've got a few cameras. This is the visible camera. But we've got five cameras in total. This is me in front of the various colors of the cameras. Here's the visible camera. And they're rotating different ways because of the way they're rotating in that pod.
And me in the near infrared wavelengths and the thermal wavelengths. All these will contribute information about the impact event, from the beginning to the end. Even seeing the crater we made we think we will be able to see the crater we actually generated in the infrared in the very last seconds of our mission.
An interesting aspect about these two images. We have filters on the two cameras so that they enhance water features. Near infrared will enhance ice features, water ice and mid infrared will enhance water features. You can see the difference in my skin tone and hair, and that is attributed to differences in actually the water and chemical and the reflected properties of my skin. So you can see by differencing these two images, you can actually learn about the distribution of the composition of whatever it is you're looking at. And that's one of the principal purposes of those cameras.
So ground based observations. I'll wrap it up with this. Again, they're equally important to the space base observations are the ground and orbiting observations. It's part of the robustness of the mission. So we go to great lengths to make sure the impact occurs over Hawaii at a good time. And this shows the impact geometry for Hawaii for the April 25th launch. Here's the West Coast of the United States.
This shows, this circle shows a 45 degree elevation angle to the moon, which is a requirement. So we're right at the edge of it here for Hawaii.
It's going to be low on the horizon for us on the West Coast, but it should still be quite observable. Hopefully with good weather, not like tonight.
And we essentially had to do this for every single possible launch date that LRO presented us.
We had a selection of a number of astronomers that are being funded directly to help us do these observations. And we had the first telecon with the entire team today. And these are the folks who are planning and are supporting the observations all the way down from the Hubbell space telescope. We have five orbits from Hubbell observing it. Oden, which is a space based platform, European space platform, will be observing it. And then a number of assets, most of which are in Hawaii, but some in New Mexico, some in Arizona, and also even in Korea.
So we also have interests from other European colleagues who want to observe it. The impact lasts four minutes. But the effect on the atmosphere could last hours to days. And we have the right kind of instruments now to really detect these kinds of things.
So there's a large part of the community that's interested in monitoring the event as it occurs and then following the impact for several hours to a day or two.
For those of you who are astronomers, this is the apparent predicted magnitude or predicted apparent magnitude at time after impact. You can see it lasts a minute and a half or so. Really starts to dim out as the ejecta gets more and more faint. The height of the cloud that this kind of brightness represents is an average, is about 10 arc seconds or so, so it's fairly large and it's fairly bright.
So we really think that this should be, with a good telescope and a clear night, observable from the ground by just about anyone. Don't need a professional to observe it.
So last slide, thank you for your patience. We'll talk hopefully in seven months with some really exciting results. Definitely going to be observable. So if you're keen on that, there's a large amateur astronomy group that Brian Day is heading up to support us.
The amateurs are supporting us now. I didn't talk about it. But there's an incredible process of actually pointing a three and a half or 10 meter. We have the CEC telescope, ten meter class telescope looking at this. How do you point that at the moon? They hate the moon. Now they're asked to point at it. Dan Wooden at Ames, a Deep Impact member, and is our chief astronomer there goes my battery. Good timing, huh?
He developed over the last six months, with a lot of hours on IOTF, the procedures for observing, actually, these events and using guide craters rather than guide stars. Normally you use a star to hold your pointing on an object. They developed a whole routine for using guide craters on the moon to point to a particular spot on the moon. They've demonstrated half arc second repeatability.
That's pointing at the moon a 10 meter theirs was a three and a half or two meter telescope to about 500 meters, kilometer or so. Incredible.
And they've been using amateur observations of the moon. Hardly amateur. Some of these images are just spectacular, because we need to get, look to the moon at all different illuminations and angles so they can understand for any given launch date what the guide crater is. So it's actually been a really good productive relationship with a lot of astronomers in the amateur community with this project. And I'll leave it at that. Thanks.
And I hope you don't have questions about the slides.
Okay, we do have times for questions. Thank you very much for an illuminating talk. We are going to ask people if you have questions to line up at the two microphones in the middle of the auditorium. Please do try to keep your questions brief so everyone has a chance to participate. I'll ask Dr. Colaprete to take questions.
>> Can the chemistry of any planet, be it the moon or Mars, can it be manipulated to eventually, you know, be able to sustain life there?
Tera forming. It would be hard to tera form the moon. It's a small body. Doesn't retain much of an atmosphere. Mars, there's lots of speculation or thoughts on that matter. There's a colleague at Ames, Chris McKay, who is a pretty strong proponent of tera forming Mars. I think it's something that's grandiose. And I'm more worried about just getting LCROSS off the ground. So it's an interesting discussion point. I actually haven't given it much thought.
>> Let's do one question per person.
I can stick around if you have a few more questions afterwards. Over here.
>> You mentioned that this impact vehicle has five cameras going in to record what happens when going in. But seems like you're more interested in recording what happens within the four minutes after the impact. Do these cameras have any useful information, usefulness after the impact, or are they gone? And if they're gone, what is your primary source of information for those four minutes?
The cameras are on the shepherding spacecraft, the following spacecraft. So that centaur, the space of the stage of the rocket is our primary impact. We're four minutes behind it. Ejecta cloud is coming up. We are flying at that ejecta cloud with our spacecraft with our instruments beaming in real time to earth all of our data.
We eventually fly through the ejecta cloud coming up. We have a side viewing spectrometer looks at the sun, watches the sunset behind the ejecta. And we monitor and then we get imaging of the impact and the ejecta cloud all the way down until we lose communication with our shepherding spacecraft, which will occur as we duck behind the crater rim ourselves, which is about two or three seconds before impact.
We're moving at about two and a half kilometers per second. So, yeah, we get all the data from the shepherding spacecraft. I'm sorry if I wasn't clear on that, in that four minutes' time. Then it impacts. And those cameras are then six feet down, and I don't think they'll survive.
But all the ground base observers will be able to see that second impact. And so we are very interested in, that could give us information on the distribution as well. Yeah. So hopefully that answers the question. Another one here.
>> Since all of this information and speculation is based on there being hydrogen in these areas, what are the other explanations of hydrogen in these areas, what are the chances of it actually working?
I didn't cover that. I should have mentioned it at least. Excellent question. That actually explains why we've got such a broad range of wavelengths, different data sets. Everything from the ultraviolet through the visible through the near infrared to the thermal. It could be water. It could be hydrated minerals. Minerals that just [claise], for example, take up water, bind water in them. So it's not water ice but it's hydrogen bound in these minerals. It could be free protons. The sun is shedding protons in the solar wind all the time. Solar protons rattle around the lunar surface. Typically they escape. And the very cold regions they can linger long enough they get trapped, chemically bound to some of the minerals. It could be free protons that we're seeing here that's just hydrogen. It's not water. It's not anything. So that's really important.
We can detect everything fairly easily, convincingly, except free hydrogen. Because you need a mass spectrometer. So we rule out water, or rule in water, hydrogen minerals, a number of hydrated minerals. Even organics.
It could be organic species. If the hydrogen is from cometary sources, which many think it is, it could be in the form we know there are organics in comets. And that's one of the things about these shadowed regions. They could be treasure troves, time capsules of all kinds of gunk that's hit the moon. All kinds of volatiles. We think there's probably C02 in there, S02. Methane can be trapped in there, it's so cold. Water. All this could be, if it found its way and somehow got buried deep enough or diffused deep enough to be protected from cosmic rays and sputtering, then it should still be there. And we are going to go take a look for it.
>> Got a quick two part question. First, what is the angle of the lunar surface as seen from the earth at the time of the impact? And, second, are there any planned spectroscopic measurements from telescopes on the earth or orbiting telescopes that will complement the capabilities in your shepherding spacecraft?
Absolutely. Unfortunately, because of, again, we don't dictate our launch date. LRO does. We're impacting just after northern summer. So the moon's got this vibration, this wobble back and forth relative to the sun and earth. And so right at the time of our impact, I think it's a little under a degree. I'll have to check. It's going to be pointed towards the earth and it's not going to be optimum. The optimum is a little bit earlier, like in June, but it will still be enough so that earth based astronomers can view it. That was a requirement and a really hard one to meet. We actually pushed back on LRO trying to move their launch dates when we run into trouble.
There are absolutely spectroscopic measurements being planned. There's a lot of imaging at different wavelengths, high speed imaging. Near spec, for example, is a very high resolution spectrometer at CEC in Hawaii. And it can see non telluric, non earth water lines. The problem for looking for 1% water in a dust cloud on the moon when you're on earth is you're surrounded by 10% water even at 40,000 feet there's water everywhere. You have to find special lines in the spectrum that are not of earth's origin, and there are some that can be viewed by these special instruments.
And they think they can see to less than 1% from the ground. And so they'll be observing. HST we're using a different approach. First, we image the moon with its ultraviolet camera to observe the impact and image the impact, and then we go to a spectrometer, a prism, to observe an emission line from the hydroxyl radical OH, and it emits at 308 nanometers in the near ultraviolet. And it's a product of water photolysis, so there's water ice or water vapor in the plume and it starts to photorize due to ultraviolet sunlight. We can see that emission line.
So we'll actually watch for that on subsequent orbits as it goes on. So, yeah, we are looking there are other folks looking for water lines out past three microns and four microns and so on. So that's some of the hot non telluric water lines I mentioned.
The flash itself is interesting. The brightness of that flash is a function of volatile content. And so if we hit someplace with even just 1% water ice, it would be maybe a factor of 100 times fainter than if you hit just dry dirt. Unfortunately, there's other things that can cause it to be 100 times fainter, too, like rocks. So that's why we're going to take all these data sets together and overlay them, so to speak, to really come up with a most convincing conclusion.
>> Hi, I'm Lu. And you mentioned there's going to be many scientists going to be observing as a team. And I was wondering if you could go into more details, such as if there's airplanes going to be going up to get out of the clouds and where you personally are going to find a cloudless observation.
Well, that's another reason why we have many observers all over the world, because if it's a clouded out in Hawaii, we're going to be very disappointed, absolutely.
SOFIA should be just the airplane stationed out of Dryden, out of Ames, will just be commissioning its science instruments at about that time. So we're definitely working with Sophia to hopefully get some measurements, some observations with them, and the instruments that will be on board.
HST. Hopefully no clouds for HST or Oden, which are very good. Speaking of spectroscopy. Oden looks in a way at the microwave for interstellar water. It's looking for molecules here and there in the interstellar space. We're thrilled. They just got a mission extension that we were hoping for. And they just got it. We just found out a couple weeks ago. That's another part of the robustness we tried to build into this, was not rely on one observatory in one place, not rely on one particular wavelength or color to look at. Really try to spread yourself around so you can take advantage.
We had a lot unfortunately, the impact itself only lasts four minutes. So you had to pick someplace where that was going to happen. Hawaii has the best instruments, in our opinion, for making these measurements. God willing it's a clear night. We've had luck. New Year's Day we had an observation on the north pole and it was blizzarding up there. And so they didn't for the safety of actually the engineers, we said don't drive up the mountain to open the dome. Stay.
So that's a risk. And we appreciate that. But that's why we have measurements on our spacecraft. That's why we have measurements on HST. There will be follow on measurements by LRO. LRO has a hard time observing it. It's at a very low altitude over the moon when the impact occurs.
And it's going to be zipping by pretty fast, and it's not designed to watch something quickly as it goes by. So they're doing a lot of preimpact characterization of this site. And then they will try to see the impact. And then they'll do a lot of post impact characterization.
And some of their instruments, if, for example, we hit some water and it recondenses out onto the surface, they'll be able to see that at very small fractions, very small amounts. They'll also be able to see the atmosphere effects very well.
So hopefully some of these assets will return enough information to answer the questions. Hopefully that answered your question.
But the team is from all over the world right now, actually.
>> I wanted to thank you for your talk. And my question has to do with the impacter. So this is an object belong centaur rocket booster.
>> And so like using your pot of flour analogy, if I were to throw a ball point pen at flour, it could hit straight in. Or if I sent it spinning end over end, maybe I'll get a better impact. Do you have any control over that?
And I showed actually some of the smooth particle hydrodynamic code data. We modeled the tin can. Pete Schultz is now just doing some impact tests with hollow cans. And actually if I had to pick an impact for this experiment I'd pick a tin can.
I wouldn't pick a Deep Impact impacter, which is a higher density copper slug. 350 kilogram slug. But we only measure down to that meter.
So if I had something that was higher density, more compact, it would penetrate to five meters, six meters deep and actually the material that would get ejected into the atmosphere, into the sunlight, would be from deeper than a meter.
A tin can, and this is a great experiment again to do with your flour, do exactly what you said. Get something hollow like a tin can. Make it a little heavier so it has a bigger impact. And then get a golf ball. And throw those various objects at it. You will get very different impacts. The tin can pancakes. It's like a belly flop. You actually only dig down a meter or two deep and so you excavate. But you throw up about the same amount of material because it's the same energy. So what happens is you get a broader, wider area that's excavated more shallow. And that's exactly what we want. We want the one meter or one and a half meter stuff. We don't want the five meter stuff.
Regarding can we control it? As I mentioned, centaur's never flown 120 days in space and then done their separation system. They've done a lot of qualification work for us to show that it will survive. There are eight springs that go around that kick them off. All their studies and tests indicate that the wobble will be minimal. And we shouldn't teeter too much during that nine hours' flight in.
We have actually, right after that separation, we turn around and we turn on some of our cameras in high speed mode to watch the centaur float away from us. Precisely to understand your concern.
Did we get a tip off? Are we going and then can we expect an end on hit or a dumbbell hit, as we call it. Most of the mass in the centaurs are in the front and back with a thin shell in between. If it hits like you said downward like this, you get a very different impact. You actually will see in the flash, the light from the flash, we'll see the two ends hit. We'll see the first and then the second on top of it.
It will still pancake flat, though, because those are relatively low density. If they hit side wards, essentially you get two different smaller impacts that are co joined by this dumbbell bar between them. It does produce a different crater. That's one reason why we want to actually do a lot of good post imaging analysis.
We really think we can image the crater with LRO both in the radar and in the visible by using the same trick that Sophia has demonstrated, imaging sky light to actually see the crater. It will help us actually understand where that ejecta material came from. Eventually we're going to use code models to put the ejecta back in and understand the depth distribution of the hydrogen as best we can or the depth of [Inaudible] that we saw as best we can from the impact. Hopefully that answers your question. It's a real fact, and we're trying to account for it as best we can. We don't have control over it. Once it goes, it's a free flyer.
>> All right. Let's thank Dr. Colaprete.
Dare I say your lecture was a hit, and we'd like to thank everyone for coming. We'll see you at the next Silicon Valley Astronomy Lecture. Drive carefully.
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