NOVA; To the Moon; Interview with Michael B. Duke, aerospace scientist and Principal Investigator for the Apollo Lunar Sample program, part 2 of 2

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A chemical signature found in some of the Apollo 12 samples. And it was quite distinctive from the composition of the basaltic rocks, the lava rocks that we had returned from Apollo 11 or Apollo 12. Creep is an acronym. It stands for potassium, rare earth elements and phosphorus. And those are the main elements that were enriched in this. It's taken 30 years to figure out what it is. And we're not really quite sure we know what it is now. But in the lunar prospector mission that was just recently carried out, the initial data show a very big, let's call it, a hotspot on the near side of the moon. And that hotspot is a spot that is enriched in creep kinds of compositions. We now think that the creep was a product of the initial differentiation, separation of the moon into a core, mantle, and crust.

And that at one time the moon was essentially completely covered with molten rock. And that it started to crystallize from the top and the bottom. And the creep was trapped in between at the time that it finally solidified. And then big craters like Mariambrium excavated that and distributed the creep around the moon. So we're still fine, you're still making discoveries? Oh yeah, no doubt about it. We don't know yet some major things about the moon, like where it came from. There are some good hypothesis better than we had before the Apollo program. What its total composition, we're still not sure that it has a core. The lunar prospector team thinks that they have determined that there is a small metallic core in the moon, but we're not absolutely sure. And it's really important that we study the moon because it is the only sample that's accessible to us of a planet that preserves the first billion years or so of the history of a planet.

We can't see that on the earth. The earth has been turned over and around so many times that it's completely lost. So what we learn on the moon can be extrapolated to the other planets, to the earth, to Venus, to Mars, to Mercury. It's very important. Do you think we should go back to the moon? So I've been advocating it for a long time with humans to establish a permanent facility there. The reasons I think that we should do that are not entirely scientific. In fact, they're dominated by my belief that we could in fact use materials made on the moon to augment our capabilities in space and to reduce the cost of operating in space. Well, the promise of the recent lunar prospector data is that there may be deposits of water at the lunar poles in the cold polar craters. There may be substantial amounts, tons and tons and tons of water. From water you can make propellant.

propellant is the major commodity which makes our space transportation systems work. If you go from the earth to Mars, you take a spacecraft to low Earth orbit and launch it from low Earth orbit. At the time it's launched from low Earth orbit, three quarters of the mass is propellant. One quarter actually goes to the planet. There's an immense amount of propellant that is taken into space and transportation costs are very high. Transportation costs could be a lot lower from the moon because you don't have to get out of the gravity well as you do on the Earth. And so if there are abundant deposits of water on the moon, there may actually be exploration or possibly commercial development of the moon. Tell me that's great. Tell me when you handle some of these samples even today. What goes through your life? Well, I have always been thankful for the opportunity to have participated in the Apollo program. I mean how many people could have done that.

And as a scientist looking at and worrying about the rocks, I mean a lot of the things I think about the rocks are remembering problems that we had one time or another. Which we overcame came for the most part. But it still is the case that the lunar samples are the only documented sample of another non terrestrial of another body outside of the Earth that we have. And as you see, they are treated as if they're national treasures, which they are. And we, of course, advocate doing the same thing for as many other planets as we can get to. Mars looks like it may be the next. But in principle, we can do the same thing on any of the planets in the solar system, at least any of the rocky ones. Just give me a highlight. What was the highlight of Apollo 15, your Genesis rock? What was that about?

Well, the Genesis rock was interesting because that was a case where one of the astronauts trained as a field geologist Dave Scott recognized that the rock was unusual and actually had to deviate from his timeline to go get it. And it turned out to be we think a sample of the original crust of the moon made four and a half billion years ago, right after the initial formation of the moon. So in itself, it just is a data point along with all of the other samples that we've collected from the Maria, from the Highlands, were able to put together a picture of how the moon formed and evolved. Great. Highlight through 16? What was the highlight from 16? Or 17? Either one. I'm just looking for a 17.

Well, the obvious highlight from Apollo 17 was the orange soil, which Jack Schmidt discovered, and they got samples of. And has ever since been a very interesting and exciting topic to work on. Turns out the orange soil represents little drops of glass that were formed in a fire fountain of a lunar volcano and were collected there around the volcano. And since then, we have learned that deposits like that exist a lot of places on the moon. So when we know something about the orange soil from Apollo 17, we can infer things about other places on the moon using remote sensing to get the data on them. We can extrapolate from what we know. And so the orange soil was very important in terms of defining a volcanic process, which nobody had even thought about before, as well as allowing us to extrapolate and integrate a lot of data that was gotten in totally different ways. Did we find out the origin of the moon? Well, there are a lot of people who think they know the answer to that question. Before we went to the moon, we had three competing hypotheses, none of which satisfied anybody, or none of which satisfied everybody.

Through studies of the moon, and studies of the earth, and models of the origin of the solar system, the current hypothesis that best explains all of the data is that after the earth formed four and a half billion years ago, it was impacted by a very large planet, maybe the size of Mars. And which blew off the moon into orbit, it didn't blow it off as a piece, it blew it off as dust and gas that then re-coagulated in orbit around the earth. And to some extent, that is sort of an integration of all of the three hypotheses that we had before Apollo. So far, it has stood up, it's withstood scrutiny for about ten years, and nobody has challenged it in the sense of getting a better hypothesis, but there's still a lot of people who don't believe it. Great. What's the hot moon called? Well, that's a long time ago, I haven't paid attention to that recently, but there were some people who thought that the history of the moon was pretty simple, that it had collected debris from the formation of the solar system that was sort of like the meteorites that fall now on earth.

There's a common kind of meteorite called con-drites, which we've studied a lot and goes back to the origin of the solar system. Some people felt that the moon had just accreted this pile of stuff, and then impacts had, of course, modified the surface. There were others who believed in a volcanic moon, one that formed, and then Lava's came from the interior and float out on the surface, and volcanoes formed, and they thought, at the extreme of that argument, they thought that all of the craters on the moon were volcanic, that meteorite impact craters were a minor feature. So those were sort of two extremes, and it was pretty clear with the first samples that the moon had differentiated, that some of the material in the Apollo 11 samples was clearly rock that had been molten or volcanic.

Now, we know now that impact melts rocks too, and so the answer is somewhere in the middle, not either one of the extremes. Well, neither was right. The answer is called hot moon. Well, in the hot moon, cold moon debate, neither was right. The moon is differentiated, but it also has also had a lot of meteorite impact, so the answer is somewhere in between. Do you remember the story of the public lined up at the Smithsonian to do the first rock moon rocks that came out from Apollo 11? I wasn't there at the Smithsonian. No, I don't remember that one. Tell me about the Russians. Did you exchange rocks? Well, yeah, the Russians were trying to beat us to the moon, but after they found they couldn't beat us with manned missions, they devised an unmanned mission that went to the mooner surface, dug up a core, wrapped it up, and sent it back to Moscow. And so when they had received their first rocks back from the moon, 100 grams of material from that far below the surface,

they, they, an exchange agreement was, was consummated, in which they agreed with NASA that they would provide us with three grams. That's about a tenth of an ounce of material from each of their missions. And we would do the same thing for them, from each of our successful missions, we, we would give them three grams. From the first sample that was returned from the Russians, we got three grams, we used about a gram of it for analysis and wrote a book. There's just that much information in, in the lunar samples. We gave them samples of each of our Apollo missions. They ultimately conducted two more sample return missions from, from different places on the moon. And we had a very, very good relation scientifically with the Russians, even through some times when, when there was some, some quite some trauma between the nations on, on a governmental level.

That's a good question. The NASA was very careful about the way the rocks were given out. They had, had a program, a competitive program that for Apollo 11 had selected, I think, about a hundred scientific teams around the world, based on proposals which demonstrated what they could do in their laboratories, what they expected to learn from the samples, how they would handle them, how they would keep them secure. And these people were, were admitted to the program. Then, when the samples came back, there was a separate team, which was called the lunar sample analysis planning team, that looked at all of the data from the preliminary examination, looked at all of the work that had been proposed by the scientists, and matched up samples with, with scientists. Then, those directions for sample preparation were given to the curator, the curator over a period of a few days actually went to the sample collection, and got the chips of rock and the little scoops of soil and put them in packages.

And then, they were given out to the, to the PIs who were told, you can come on this day, so everybody came and, and stood in line, and, and then it was sort of like, oh, anyplace else where you have to sign papers and, and, and to receive something, you know, registered mail or something like that. You, you go to the post office, you pick it up, you sign for it. Well, associated with the Apollo program was a very strict security responsibility. These people had to guarantee that they were going to keep the sample safe, they were not going to lose it, they were not going to use it outside of what they had said they would. So, there was a lot of documentation, each one came and had to sign papers again, and had to look to see that their sample was the right one, and so forth. And, you know, there were 100 teams, and everybody wanted their samples first.

And, I don't really quite remember whether there was a lottery or whether they went alphabetically, but, but there were lines of people waiting to pick up their samples. What about, what's in there? Well, these are three principal rock types of the moon. The one on the right is a volcanic basalt. It was formed about three and a half billion years ago at the Apollo 15 site, and crystallized from a melt, from molten rock. The little holes that you see is where gas was trying to escape as the rock crystallized. These rocks are principally found on the front side of the moon and are responsible for making the parts that are dark. Now, these two, this rock in the center is from the Apollo 16 mission, and it is actually also a molten rock, but it's not a volcanic rock. It was molten in a huge meteorite impact.

One of these very large basins, which is 100 kilometers in diameter, was formed by a huge explosion, or essentially explosion, collision of a big object, and that melts a lot of material, and this is a sample of that kind of melt rock. What are these rocks, these rocks right here, just looking at these? Well, one of the things that we found out from rocks like this is when did it happen? Because whenever a rock is molten and crystallizes, the crystals remember when they formed. They do that by through their contents of radioactive materials, which decay after that, and you can come back in at a later time and measure how long it's been decaying in that place. You can tell the age of these rocks, and those rocks typically are about 3.9 billion years, our rocks that were formed after the moon had differentiated into a core metal and crust, but largely before the rocks filled the marine.

This rock on the left is also an impact rock. It was formed by one of the major collisions early in the moon's history, and the importance of this is that it contains fragments that are from earlier, from before. This is the type of rock that we go to to get samples of the original lunar crust, and we can tell what its composition was, what its age was, over what period of time it formed, and so forth. Thanks for watching.

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