>> From the Library Of Congress in Washington, D.C. >> Michelle Cadoree Bradley: I'm Michelle Cadoree Bradley, a research specialist in the Science Technology and Business division of the Library of Congress, and I'd like to welcome you to today's program. Walking With the Last Men on the Moon. Revisiting the Apollo 17 landing site, with the Lunar Reconnaissance Orbiter. Tomorrow, December 7th, is the 44th anniversary of the Apollo 17 launch. The last manned mission to the moon. Today, we will revisit the landing site with our guide from NASA, Dr. Noah Petro. He is a lunar geologist and the deputy project scientist for the Lunar Reconnaissance Orbiter, which launched in 2009. Dr. Petro became interested in geology in high school. He has received a BS in geology from Bates College where he was introduced to the field of planetary geology. He has a PhD in geological sciences from Brown and was a NASA Post Doc before becoming a research scientist there in 2009. I also understand that he has a familial history with NASA, which perhaps he will go into, but if not, I encourage you to review his NASA scientist interview which is available from the NASA website. Please help me welcome Noah Petro to the Library of Congress. [applause] >> Noah Petro: Wow. Alright, well thank you very much for that awesome introduction. I'm really quite humbled to be here today to talk to you about something that I care deeply about. As mentioned, space exploration is sort of in my DNA. My father, when he graduated from college in the early 1960's immediately took a job working for a contractor working for NASA building parts for the Lunar Module and for the backpack that the astronauts wore when they were on the surface of the moon. So for instance, in this picture here of Jack Schmidt standing on the Apollo 17 landing site, my dad built parts for the backpack there. And actually, as a kid, that really didn't resonate with me too much. I don't think most kids really care all that much about what their parents do, as long as they're there to take them to baseball games or whatever it is. But we were at a museum, The Cradle of Aviation Museum in Long Island and he started, he never really made a big deal about it, we go to the air and space museum as a kid of course and that was awesome and we talked about Apollo. And hey, kid, people went to the moon. And things like that. But then at the museum, he said, oh you see this piece? This was part of the backpack and I helped build that. Wow! And you know, one of the things that we did and nobody knows this, he told me. And he pulled me aside and said, see that piece of metal that sort of holds the whole thing together, it doesn't really do anything except hold the backpack together, the guts of the backpack together? Well, all of the engineers, when we were finished building one, we take out the etcher, the metal etcher, and sign our names on it. So at some point in the future, although we know that each of the Apollo landing sites are preserved or intended to be preserved, if someone were to go and crack open one of the twelve backpacks that are left on the surface of the moon, there will be the scribble that if you could decipher it, it would say Dennis Petro. So it is a proud heritage of studying the moon and revisiting some of the work that he did in the 1960's to help get the astronauts to the moon. If you've ever seen the Apollo 13 movie, there's the famous scene where the astronauts are trying to take the round connector and put it in the square hole. He built the round oxygen exchange canister that was in the lunar module. So it's with a lot of gratitude that I come to talk about Apollo 17. As mentioned, tomorrow morning, the wee hours of 12:33 in the morning will be the anniversary of launch and really start the celebrations, as limited as they may be, for the 45th anniversary of the Apollo 17 landing which will occur next year. Before I get started, though, I want to take a moment to talk about why I care about or why I think I care about the moon. I got a colleague of mine, Jim Zimmlin, who works at the Air and Space Museum and the Center of Earth and Planetary Studies, if you were to ask him this question he would have a different answer perhaps. So this reflects my thinking on why we think the moon is important. And I'm talking about my home team here. I was vested interest in the moon, obviously, but I think of the moon of the cornerstone of understanding how planets work. We can learn about a lot by studying the Earth. That's why we go out and study lava flows in Hawaii. How do planets work? But the Earth is not the best example of a planet. We have our lovely atmosphere, we've got water that erodes the surface. If you look at the other planets, large objects in our solar system, outside on the table outside in the hall, I encourage you to pick up the information about the new Verizon's mission which flew by Pluto several months back. Those images of Pluto reveal a world that's unlike anything, at least I expected. But our understanding of the moon is what helps us interpret the record of the surface of Pluto, of Mercury, ultimately of any object in the solar system. My mind goes back to understanding what's going on on the lunar surface. Because the moon is close to the Earth, it took the astronauts three days to get there. It is a neighbor. I like to think of the moon as sort of the Earth's attic. It's where the ancient record of the inter-solar system, our corner of the solar system, is recorded. In the rocks on the surface of the moon. And because we have the six Apollo landing sites, we have those successful missions that brought rocks back to the Earth. Those samples tell us something very important about how the moon evolved, and by association we can use those rocks to understand how the moon evolved and how planets work in general. But one of the things that we get from our mission that's orbiting the moon right now, The Lunar Reconnaissance Orbiter, is the context for those samples. A rock is a wonderful thing, but a rock with context where you know exactly where it came from, where it's history is that you can use to tell a story, tells a lot about how a planet works. And so what I'm going to talk about in the latter half of my presentation, is the context of some samples that we got form Apollo 17 and how the new data we have helps us better understand what those rocks are telling us. We're here and building a facility that's devoted to the history of the written word. The rocks, I like to think of rocks as kind of like little books. It's up to us to understand what those books are telling us. A rock without context is like one of the middle books of a volume. If you took book three of Harry Potter, well you don't know what went on on either sides. But if you have context, the full volume of an encyclopedia or Harry Potter, you get a better sense of the whole story. And so when we get the context of these samples, whether it's through the images the Apollo astronauts took or those images in the context of the entire planet and the globe of the moon, that tells us something very important about how the moon works. So that's my preamble about why I think the moon is important. Hopefully, if you're convinced, that's wonderful. If not, well let's at least enjoy talking about some of the things that I do on a daily basis. This is one of those awesome external rocket camera footage that we get from rocket launches. This was in the late afternoon of June 18th, 2009. The launch of the Lunar Reconnaissance Orbiter. This is in the pre hi-def day, by the way. I sort of shutter to show this. But it is still pretty spectacular, the launch of LRO. Now, LRO has been at the moon for over seven years. That feels like it's gone by pretty quickly to me. But the seven years that LRO has been at the moon is important, and not just because that's seven years of funding for someone like me to work on the mission. But it's seven years of studying the moon in a way that we've never been able to do before. Oftentimes, what we do in planetary science is we go to a new object, we go to Mars, we either fly by it as we did in the case of Pluto or we orbit it very shortly. What's happened at Mars with our long duration of orbital missions and indeed now what's happening at the moon, is we're not measuring the moon in ways we've never been able to do before. We're actually able to [inaudible] the changes that occur on the surface of the moon. We're finding new impact craters that have formed in the last seven years. Now if you're like me, first of all I apologize for that, but if you're like me you go to Google Earth and maybe you look at your neighborhood, and you use the little slider to see what your neighborhood looked like ten years ago, twenty years ago. We can do that for areas of the moon now. We can see images from eight years ago, not eight, six years ago, and images taken yesterday and compare them and actually see changes that are occurring on the surface of the moon. Why is that important? Well, before LRO we had no idea the rate at which the surface of the moon changed. And as I said before, our understanding of the moon is what we use to leverage our understanding of all other objects in the solar system. So when we learn that the moon is dynamic, it's changing at a very slow rate but still changing, that tells us something important about what's happening on asteroids, Mercury, throughout the solar system. Indeed, one of the most interesting implications relevant to the Apollo landing sites is those beautiful footprints. We're all familiar with the image from Apollo 11 of Buzz Aldrin's boot print. And the thought for years was that that boot print would be visible for millions of years. It turns out that the rate of change, the new impacts and the turning of the surface of the moon is happening much faster than we expected and that boot print may disappear in the scale of 100,000 years, not a million years. Now that may not seem all that important but again, we are using the moon as a natural laboratory to understand the process that are affecting all of the planets in the solar system, including the Earth. So LRO, and I'm going to show a lot of pictures today. Because pictures are worth 1,000 words but LRO has many, many instruments. Seven instruments, in fact. When LRO was launched in 2009, there was a plan that we would eventually send humans and robots back to the surface of the moon. And so we wanted a Reconnaissance mission. A mission that would find the safe and interesting landing sites. That would tell us where to go and how to stay at the moon safely. And so these instruments were selected to find safe places to basically pave the way for human exploration into deep space. They're also selected to help us find places where you might find water or [inaudible] at the moon. One of the objectives was originally to send humans to the moon to live off the land. And one of the ways to do that is to not have to bring all of the water and oxygen with you. So we wanted to find places where we could get water from the lunar surface. And so we have instruments ranging from a radiation detector that measures how much radiation damage a human might expect when they're traveling to the moon. We have a thermal instrument that measures the surface temperature of the moon, an instrument that will measure reflected starlight that's light not form our sun, but light from all the other stars in the galaxy that reflect off the nice side off the moon to suggest where water might be. We have a neutron detector that can map out where hydrogen is present, commonly in the form of oxygen or OOH. We have a laser instrument that measures the surface topography of the moon with a precision greater than any object that we have in the solar system. We have the best topography, not to sound like a future President. We have the best Topography in the solar system at the moon thanks to the Lola instrument. The L Rock instrument, a camera which is actually 3 different cameras, has mapped the moon at resolutions of approximately fifty centimeters per pixel. We're going to see a lot of those pictures today. And a radar instrument that allows us to peer beneath the surface. Kind of 3D glasses, x-ray glasses to see what's going on in the first upper meter or so of the surface. That gives us a sense of what's happening to the lunar surface. Also, it's been used to map out the presence of ice deposits near the lunar poles. So all of these instruments combined gibe us this really incredible view of the moon that we've never had before. Because we've been to the moon, we went with the Apollo mission six times, several times to lunar orbit with Apollo, we have a misguided sense that we know everything about the moon. And I think one of the things that we're learning from LRO is a lot of our presumptions about the moon have been wrong, or if nothing else, incorrect. Now just a few other moments of promotion, I encourage everyone if you haven't gone to the second floor of the Air and Space Museum, there's an exhibit devoted to the results coming back from LRO, particularly from the camera. This is Mt. Marilyn and again for those of you who remember the Apollo 13 movie, Jim Lovell who had orbited the moon previously on Apollo 8, named this mountain after his wife. So sometimes in the movie you'll hear him talking about it. This is an LROC image again high resolution, oblique out of the, I think of it as the window view although we don't actually have windows on the spacecraft, we tilt the spacecraft to the side to get an image like this. But there's an entire gallery devoted to images from the LROC instrument. The gallery will be open at least through the end of this year, so you have at least one more month but I've been told that it's likely going to be there into the early part of next year until they find something to replace it. It's definitely worth the visit. I would normally say it's on the side where the lunar module was but that doesn't help. It's like getting directions from someone in Maine. You go to where that place used to be. It's on the McDonald's side of the-- everybody knows that. It's on the McDonald's side of the museum. The second floor. A few other just upcoming events that we want to make sure everyone is aware of. On August 21st, there will be a total solar eclipse. The path of totality crisscrosses the country going from Oregon all the way across through South Carolina and out to sea. Even in D.C., we'll get a really nice show of partially obscured sun but we want to remind everyone that the central player in a solar eclipse is the moon. And again, because we have a very accurate representation, we have an accurate dataset of the topography of the moon, we can actually predict with a really high degree of accuracy, the exact shape and path of that eclipse that goes across the central part of the United States. In fact, we have an understanding of the topography of the moon to such a degree that the uncertainty is down to about a second or so of the timing of the eclipse are not due to any uncertainty of the shape of the Earth or the moon, it's actually uncertainty to the shape of the sun. So basically, we can blame all of our friends in helio-physics for not standing up and getting enough information to us. So that should be a really great event next summer. October 28th of next year also is another event that the LRO mission supports and that's going to be International Observe the Moon night. If you go to observethemoonnight.org you can learn more about that but there are events all across the world actually where we get people out looking through telescopes and thinking and learning about the moon. Ok, so Apollo 17 and 44 years later. So I would highly recommend that everyone wake up, when you turn your phone back off of sleep mode, wake up at 12:33, go to the website, a friend of mine Ben Feist who is here today created Apollo17.org and at 12:33 the mission will play out in real time over the next ten days or so, as the mission unravels. And it's a shameless plug. There's no money gained from it, it's just for the sake of knowledge. But Apollo 17, they saved the best for last ultimately. It was the first night launch of the Apollo mission was viewed up and down the East coast and really was the climax of the entire space program up to that point. You had the Mercury, Gemini, and the preceding Apollo missions all in my mind building up to this moment, where we could get astronauts to go to the moon, live on the moon for three days, work, drive a car, commute, no traffic not like here. But it also represents the last time that humans traveled into deep space. The astronauts were very fortunate. In August of 1972, some months before a large solar flare passed through the sun, passed through the Earth moon system. Had astronauts been on the moon at that time, there could have been potentially serious medical effects to them. They dodged a solar bullet, as it were. There are hazards to exploring deep space and they were very fortunate. All of the Apollo astronauts were very fortunate to make the roundtrip as President Kennedy outlined. So for a little context of what lunar expiration is like, this is a map put together by the camera team. Normally I like to wander towards the screen. I like to gravitate towards the moon. I'm going to try to stay close to the microphones for a moment here. This is the hemisphere of the moon that we're most familiar looking at. And actually, the image of the moon here you see is stitched together with hundreds of smaller images to make this beautiful map of the moon showing the relief of the moon, the texture of the moon. Now in grain and barely visible here are all of the Apollo landing sites. Apollo 17 is here, Apollo 11 landed to the South, 12 and 14, 15, 16, 17 now. Just as a reminder, there's an entire half of the moon that's not shown here. An entire hemisphere that has never been explored on the surface. And as I very gingerly lean over out in front here is a lithograph of both the near and far side. I would encourage everyone to grab a copy. I say that because there is a whole half of the moon that has not been explored. The surface area of the moon is roughly the size of Africa. If I were to tell you that we've been, I've been to Africa six times and I've seen everything, I've learned everything there is to learn about Africa, I'd be laughed off the stage. We've been to the moon six times with humans, we have three robotic sample return missions sent by the Soviets, all in a line here. And several other landers all across the near side. But again, there's an entire half of the moon that remains unexplored. Just as a bit of a preview, there's a feature I'm going to be talking about a little later on. The tycho crater here. This is a very bright feature that's visible to the naked eye when the moon is full, but I do that as a bit of a preview to call back. The LROC team has an amazing website with clickable, searchable images. I encourage you. There's a lot of wonderful time-syncs, real news that you can explore by seeing what's going on with the camera. It's amazing images that the camera is returning. Ok. So again as a bit of context for what's going on in 1972, and again because we're at the Library of Congress, I hold up the Apollo 17 preliminary science report. Nice, light reading. This was drafted sort of in the immediate aftermath. Each of the missions had a preliminary science report. But what that served as the first digestion of what we learned. It's really an impressive document and I spend fafr too mich time leafing through it because there's so many wonderful nuggets. Now this is a bit of inside baseball information here. I was not born in 1972, so looking back at what was going on really offers an insight into what was happening with science at the time. And there's this quote that I pulled from the preliminary science report which sort of blew my mind. In the past decade, there have been two revolutions in planetary science studies. There has been a revolution in new global tectonics, describing the motions of continents and the generation and destruction of the sea floor. That's right, I forgot-- 1960's, this revolution. The theory of plate tectonics was deposited and shown to be feasible. This is happening almost contemporaneously with the Apollo program. With our return of samples. And so the second half of this quote, and it's investigations of the origin, history, and formation of the moon, the Apollo program has led to a-- and you can all read. I'm just reading this because-- providing the first deep understanding of a planet other than the Earth through the development of new techniques of exploration, investigation, and analysis. And through the integration of scientific knowledge, gained an interdisciplinary fields. And another really important side effect benefit from Apollo is the advancement in analytical techniques and also bringing in of researchers into studying samples. Now I'm very fortunate to work with a number of people who are on the front lines studying Apollo samples. And they're still active today. Fewer and fewer every year. Every year at our conferences, the old timer group is getting a little bit smaller. Still as vocal as ever, but smaller and smaller. But it was this period in time where there was an advancement of scientific analysis techniques of the instrumentation, partially because of the samples coming back that we knew we needed to study these samples to really make the scientific investment in Apollo worthwhile. So all of this revolution [inaudible] the Earth is being accompanied by our understanding of the moon and our sort of advancement in exploration through the rest of the solar system. Earlier, I mentioned that Apollo 17 was the final mission. It was the last of what we call the J missions. Heavy-duty scientific experiment laden missions with the rovers. It had ten surface experiments to take on the lunar surface. Ten were conducted in lunar orbit. This is a plot, again, from the preliminary science report of basically the distance the Apollo astronauts traversed while they were on the surface. Apollo 11 didn't leave the infield of the baseball diamond. They just got out and walked around the immediate vicinity of the lander. By the time Apollo 15, 16, and 17 came along with the rovers, they were driving over 20 kilometers across the lunar surface. The massive of experiments that were brought to the surface and left on the surface was increasing. The time outside of the lunar module was now well over one day, 24 hours spent outside the surface of the lunar module. And of course, then the weight o the samples brought back was increasing dramatically across that time. Has anybody, how many people have ever been to the British Museum or have seen the Rosetta Stone? Ok, the Rosetta Stone is this iconic figure in our understanding of Ancient Egypt. And if you ever go see the Rosetta Stone, it's this beautiful [inaudible] It's a beautiful rock with all of the-- etchings and words on it are nice too. But the rock itself is beautiful. The combined mass of the samples brought back by Apollo is almost exactly to the kilogram half the mass of the Rosetta Stone. Now, the mass of the Rosetta Stone doesn't matter. It's what's written on that one side that matters most. I think there's this misinterpretation that, oh there's truckloads of rocks that came back from the moon. No, these are precious samples and I've said this before: putting those samples into the context of where they were collected, what they tell us about not only that spot on the moon, that region, but then by association that we have with the data from orbit, the rest of the moon is really, really important. Now there's one other experiment, and I put in quotes experiment, that was brought to the surface on Apollo 17. And as I was putting this talk together I got maybe a little carried away with this thought, but there was one experiment that was the culmination of decades of development. And particularly the Mercury, Gemini, and Apollo programs. And that experiment was in the form of Dr. jack Schmidt. Harrison Schmidt. He was the first and thus far only geologist to walk on the surface of the moon. He was the last one to get out of the lunar module, the twelfth to walk on the surface. He was in the first group of scientist astronauts selected by NASA in the mid 1960's, and he had participated, once he was selected, he had participated in the training for prior missions and helped in the analysis of samples that were brought back, as well as the other surface investigations. So he was intimately aware of what the prior missions had done, their results, and what I want to at least leave you with here is the importance of having, hopefully we'll be at a position in the not-too-distant future we'll have astronauts going to the surfaces of objects. Having a geologist, a trained geologist, part of that process is very important. I know Jim has worked in the field with several astronaut candidates, has participated in some events working with astronauts. The ideas of getting trained scientists on the surfaces of planets is very important. Because what they can do is not only call upon their decades of experience in the field, but also kind of put together a synthesis of what the results of that investigation are. We benefitted not only by having Jack on the surface of the moon then, but also now 44 years later working with him to reanalyze what he did on the surface of the moon on those three days in 1972. And so one of the benefits that I feel is happened strongly today is not only he gets the right samples but he's helped us tell that story. Again, take those stories each rock tells us and weave a narrative. A history behind those rocks. So let's go back to why Apollo 17 was sent to the moon and what its objectives were. Now Apollo 17 was being planned in the early part of 1972. This was hot on the heels of Apollo 15 but before Apollo 16, and there were five objectives laid out. This is defined by an August panel of leaders saying that they wanted to sample ancient lunar crust. As far from the Apollo 15 landing site as possible. When I showed you that map of Apollo landing sites, they all cluster in a region roughly around the equator, but they are also very close to one large feature. The imbrium basin. They wanted to get a landing site as far from the imbrium basin as safely possible so that they could gather the diversity of the lunar surface. They wanted to sample what they thought were young volcanic rocks. Most of the volcanic rocks that we got back from the moon are the order of three to four billion years old. And they wanted to try to get rocks that were younger than that. Volcanic rocks that were younger than that. They wanted to get improved coverage by the orbiting command module. The command module orbited sort of in a roughly hula hoop band around the surface of the moon that passed over each of the landing sites. They wanted to get coverage that improved upon the prior missions. They wanted to be able to deploy geophysical elements on the surface, but also in an area that had some surface layers. They're looking for a volcanically covered region to measure the thickness of those volcanic layers. And then also deploy the experiments that would then subsequently be left on the surface of the moon after the mission concluded. So the Apollo 17 landing site, and there's my first typo of the day, was selected on-- this is not an Irish spelling. This was on February 11th, 1972. So just keep in mind, so they have had, at this point they had essentially one year or just under a year, ten months to plan the investigation at the Taurus-Littrow Valley for Apollo 17. So with these five goals and the identification of a landing site, specific traverses were identified to address those five topics. And so using images that came back from the Apollo 15 mission, and these prior missions all shouted for each other. They were all imaging potential landing sites for future missions. Five different units, five different areas within the Taurus-Littrow Valley here, five different units were identified. It may be a little hard to see in the screen here, but there is this light debris material, this light colored unit called the light mantel deposit that they wanted to sample. There's the dark mantel deposit and this is a larger unit where the floor of the valley, this dark floor of the valley, appeared to have some kind of covering. The craters that you see on the surface all appear to be somewhat degraded. You ever picture your lawn or your front yard or some large area on a snowy day everything, your wall, gets a little bit subdued. So there was this hypothesis that there was some covering material, something covering the floor of the valley here that they wanted to sample. They wanted to sample whatever was below that, the subfloor. They also wanted to get material from this unit here. This is called the sculptured hills. This has a slightly different texture. To use a very technical term, lumpy, compared to these mountains to the North and South of the valley that appear to be-- to use another technical term-- mountain like. There are these little knobs in the sculptured hills where the [inaudible] appear to be one large, coherent unit. So with the identification of these five different units, traverses were identified based on the optimal landing site in the middle of the valley where the astronauts could drive around the valley to sample these different materials. Just as a point of comparison, talk about the Taurus-Littrow Valley and a little bit of scale, this is the Grand Canyon on the Earth. This is, again, using that amazing tool Google Earth, and this is a transect through the Grand Canyon. So this is about 30 kilometers from end to end. Covers about a kilometer and a half, 1.8 kilometers of relief. For comparison, this is the Taurus-Littrow Valley, same 3 thirty kilometers across. This is two and a half, 2.3 kilometers of elevation change. So this is another important thing to consider here. With the first Apollo landing, Apollo 11, they landed in what they thought was the smoothest safest landing site, as far from hazards as they could. And of course when they tried to land on Apollo 11, they were headed right for a boulder field. And so Neil Armstrong had to steer the lunar module away from those boulders. Just four years later, they were able to land in a valley deeper than the Grand Canyon. That's an incredible advancement in a very short order, going from finding the safest landing site to landing in a valley where you have towering mountains on either side of you. That was quite the accomplishment. Ok, so let's now look after mission. How did the-- let's give the astronauts, let's give the Apollo 17 crew an evaluation. How did they do? So, for those pre-flight objectives, they were indeed able to go and sample this light mantel deposit, this debris flow. And an interpretation was made from-- an interpretation from the origin of this debris flow was made that material from that tycho crater, and I showed you that image earlier. Tycho crater is located over 1,000 kilometers away from the Apollo 17 landing site. That objected material shot out of that crater, landed, hit the top of the South [inaudible] and triggered a landslide. So the interpretation was that the astronauts sampled this material that was estimated to be about 100 million years old, was caused by the formation of that crater, 1,000 kilometers away. And so this is one of the beauties of lunar science is that you can have an event 1,000 kilometers away trigger a landslide here, and we can go and sample that landslide and get the age of that crater. So that's handy. And as a reminder, geologists are very interested in organiza-- if you ever come to my office, you may not think that geologists are interested in organizing things, but indeed we like putting events into some sort of sequence. And so getting the ages of events is very important. So an interpretation was made that the samples collected from this debris flow were triggered by that impact 100 million years ago. The second objective was to sample the dark mantel, and that proved to be difficult. And again, in this preliminary science report, interpretation was made that that origin of that dark mantel deposit, the subdued texture of the surface, remains one of the enigmas of the Apollo 17 missions. So we can't necessarily say that that was addressed. Now, they did however sample much of the subfloor. This volcanic fill that flowed in and filled the valley. They sampled that quite extensively. The fourth objective of sampling the sculptured hills, now one of the last stations on Apollo 17, station 8 here, which the primary objective of which was to sample the sculptured hills. But at the time it remained uncertain. And no more is known about the sculptured hills unit than it is indeed different. It looks different than the [inaudible] to the North and South. And so this remained an open question of whether or not any material from the sculptured hills were ever sampled. And lastly, the [inaudible] and those were sampled very well. And as I'll show in a moment, several stations were along the base of the [inaudible] Of course they could not drive up the [inaudible] but instead of having to go get the rocks, the rocks came to them. Several boulders were observed to have rolled down the hills well before the mission. These were boulders that were seen in preflight images. And so they drove to the boulders knowing that they came from somewhere up the mountain. And so those were sampled quite well. So Now, this is the Apollo 17 landing site. The Taurus-Littrow Valley as imaged by the camera on LRO. Again, so this is an image from 1972, here it is today. Looks the same. Again, those changes that are occurring on the surface of the moon are occurring at smaller scales than what we can see even in this particular image here. Apollo 17 landing site is marked very small right here. Right in the middle, essentially, of the valley, giving easy access to these units that they wanted to sample. In addition to wanting to put things in order, geologists like naming things, so these were all craters and features that were named by the crew to help in communications, and then in yellow is the traverses that they took. Over 20 kilometers of traverses, starting with the very first traverse on day one, traverse two, and finally, traverse three. So let's sort of retrace their steps a little bit and evaluate some of the open questions that they left that still remain-- well, remain unanswered until today. But for a bit of context, just to help drive everybody, this is the traverse in the context of D.C., so we're sitting in a building right over here. A colleague of mine, Brent Gary, who works at Goddard and is a colleague of Jim's back here, made this really helpful map. If you put the landing site right on top of the Smithsonian Metro which on a normal day isn't that easy to get to, but landing a lunar module on it might be the best way. They were able to cover quite a bit of distance getting not only on day one close to Nats Park but not all the way there. But day two going well into Arlington, and day three up into Northeast D.C. Somewhere in here is a joke about either the metro or local traffic but I'm not quite sure how best to make that. Fortunately, they didn't have to contend with traffic. But this does give you a sense. That they were able with the rover to cover quite a good amount of distance. So that landing site, so here's the Smithsonian Metro Station, this is an image from the camera and all of these black streaks on here are traces of their boot prints or in some cases, and if you get real close, and normally I'd say [inaudible] and take a look, you can actually see two parallel lines. Those are the tracks of the rover. The wheel tracks still there 44 years later. The next slide is actually going to be a series of images. Pretty much every time the spacecraft passes over any of the Apollo landing sites, we take an image of it. And so what I'm going to show here is a series of eighteen images. We passed over the site more than eighteen times, but eighteen illuminated times-- showing basically the landing site as a function of solar angle. Basically time of day. From morning to nighttime. And it's going to loop and will let me talk a little bit about some of the things that we can see. Good, it works. Ok, so at center here is the descent stage, the bottom half of the lunar module sitting on the surface today. There's the shadows creeping along. This black spot here is the lunar rover which is parked at the culmination of the EVA's sitting on the surface there. And the west is the [inaudible] station, scientific experiments that were set up and left operating for about five years until they were shut off in September of 1977 prematurely. So you can very accurately retrace the steps the astronauts took. There was an experiment that was set up here as well, so we can literally follow the footsteps of the Apollo astronauts. There's one other feature that moves around here that you might follow. I'll take the laser pointer off, you'll see a spot moving, a shadow moving across the surface. Anybody want to venture a guess at what that shadow is? Jim, you can't answer that. Ben, you can't either. You know the answer. Yes. So one of the great mysteries-- mystery in the sense of what will we find, and one of the great questions, is will we see evidence of the flags at the Apollo landing sites? We know that the Apollo 11 flag was knocked over when they lifted off. There's footage of that from the lunar module as they lifted off, the flag got knocked over. 12's flag never deployed properly. There's a rod that hangs it out so it stands out at attention beautifully. But there was a question of whether or not we would see anything. Now if you ask me, before the mission I would have said no. there's no chance that the flags are still there. This flag is probably as well if not better designed than the flags that are brought there. They were off the shelf, not quite go down to the local hardware store but essentially had an objective of lasting three days on the moon and that was it. Well, we get these pictures back and there's only one thing that can cast a shadow like that and some of the images taken of other landing sites, you can see. I'm sure the flag has been bleached. You leave a colored shirt out in the sun too long over the summer it will bleach white. I'm sure that any color that were on the flags were bleached away but nope, they flags are still standing. Ok, yeah that's a good question. So this is about 100 meters right here. So a football field. This lunar module, and I would encourage everyone to go over to the Smithsonian to see an actual lunar module. Well not one that flew, of course, but a lunar module. So this covers about, all told, about 400 meters across. This flag was put about twenty meters to the north of the lunar module. They learned from Apollo 11 that having it too close meant that it got blown over when they launched and so no one wanted to knock over the American flag a second time on the surface of the moon. So if nothing else, that was kind of cool. As a quick aside, there's a letter in the NASA archives at NASA headquarters of someone violently complaining as a lot of people tend to do, of the waste of sending flags and why would we spend the extra money, and some very dutiful NASA civil servant wrote back saying well, here's a copy of the receipt for those flags. It was like five bucks. It was a lot of talk about investment and so this is not a huge expenditure of resources to get flags to the moon. Ok. This is a fly through that the camera team produced to just highlight some more of the hardware. I think, ok so here's the descent stage of Challenger. You can still see the footpaths. This is where the ladder where the astronauts exited and entered the spacecraft. There's your flag still standing on the surface. The experiment packages that was called the [inaudible] deployed on the surface. There was over ten experiments that were brought to the surface that were designed to last upwards of twenty years but we're going to shut off after five years. Over to the east of the landing site is the surface electrical properties experiment and then to the South is the lunar rover. There is a documentary put together by CNN called the last steps that should be aired sometime this week. It's available online if you Google The Last Steps. But some of the footage that's impressive, especially of the ascent when the lunar module took off. Let me go back one moment. Camera mounted on the lunar rover actually shows the astronauts taking off from the surface and then pans back around. And you can see the orientation of the flag as it was then and you know, that was the last time. December 1972, that humans ever touched space. And it really hasn't changed at all since then. Ok, so now I'm going to revisit in the time that I have left three questios that we've been able to address using LRO and modern data in a peper that-- and this is #HumbleBrag. Jack Schmidt was interested in looking at what data we have for Apollo 17 and so he put together with the help of myself and several other people, a paper not quite as thick as this. It feels like it's that thick, though. A really deep investigation into the Apollo 17 landing site with modern data. And so we're going to address these three questions. What is the origin of that light mantel deposit? Where was this sample? Sample 70019. Where was that collected? And there's an interesting backstory to that. And was sculptured hills material sampled during the mission? So let's talk about the light mantel deposit. So this is a very quickly sped up video produced that Ben has posted to his website, apollo17.org, that allows us to follow the astronauts as they begin traverse two. EVA two. Starting at the lunar module and driving all the way down to the South maseef. This is easily about five kilometers of driving that they had to do to get there, over quite a long time. Stopping several times not for rest breaks, but to sample the surface. As they got to the base of the south maseef here, they actually had to drive up this ridge. This is a tectonic feature called a wrinkle ridge where two parts of the lunar crusts essentially collided and one went on top of the floor here, creating this ridge. So this second traverse, this EVA two, was designed partially to collect material of this light mantel deposit. As I said before, the assumption was that the light mantel deposit in Apollo 17 is here, came from tycho crater. And you can see the beautiful streaks of material coming out of tycho crater. The thought was that some material was ejected, impacted the south maseef and caused this avalanche. So this is an image from the LRO camera taken when the sun is very high in the sky as you saw in that animation of the Apollo 17 landing site that depending on what angle the sun is with the sky, you can make out different things. When the sun is low in the ground, you can see boulders, craters, surfaces, very well. When the sun is high in the sky, seeing those features becomes very difficult but you can see differences in color very clearly. The bright tracks, the bright lander, the dark rocks beneath. Here is this debris flow. And something that came out to us in this investigation is that it appears that there's a darker debris flow here and a lighter debris flow here. Now it's very possible that this lighter debris flow covers this darker unit here, but it's apparent to use that instead of one massive landslide coming off the South maseef, it appears that there are two. The darker one in the subsequent unit, this lighter one here. And so what this tells us is that perhaps this debris flow represents multiple events and not one single triggering event such as the placement of ejector from tycho crater. Just as a slightly different perspective, this is again one of the out the window views. These oblique's. Again, taken from somewhat high sun so you can see the differences in the original image, anyway, you can see the differences of the younger flow and this older flow. Here's their landing site here. And so what this potentially tells us, and this is at high sun here and so that becomes very apparent, or at least becomes apparent that there are these two debris flows, is that perhaps there's multiple events triggering these avalanches on the lunar surface. So that sort of gave us one of those moments when we think what have we done? Are we wrong? What could cause these avalanches. I pointed out moments ago that there are indeed those tectonic features, those scarps. This is this data from our radar instrument. And again, the radar instrument lets us look slightly below the surface. Deeper into the surface. Here is that fault, that scarp, it's called the Lee-Lincoln scarp. The valley here is seven kilometers wide and you can barely make out here the outline of at least the younger debris flow. But it looks like there may actually be a second fault that goes along near the older landslide as well. So our conclusion, at least at this point, and it's explained much more in the paper, is that instead of having to rely on objector from a crater 1,000 kilometers away, these landslides that were sampled very well by the Apollo 17 mission may actually even be triggered by a much more localized event. Indeed, moonquakes forming these tectonic features. And so that's sort of a big shift in understanding. We've used that age of tycho for samples now for 44-45 years. Turns out that tycho is probably still very young but we may have to remove tycho from one of those features on the moon that we know it's precise age. Something that we do know precisely well is now the origin of this sample. Sample 70019. This is sampled by Jack near the lunar module at the culmination of his second EVA. Let me pull the curtain back a little bit. I was making this slide and I was thinking oh, how am I going to explain this sample? I could get into some of the technical details but I don't have to. I'm going to let Jack explain a little bit about what he did. And so-- >> Hey Bob? >> Go ahead. >> I cheated on you. >> I was sure you would. What'd you do? >> I just sampled a glass from the bottom of a crater. I documented it by shooting the limb across the crater [inaudible] and it's eleven feet and in that prospect it's seven. And then I sampled it. >> Ok. >> It's very fragile. That's right. Very fragile and I double back and I don't know if we can keep it or not. We need to think about how to preserve it. >> Ok. >> Noah Petro: So this is from Apollo17.org. Again, it's you'll spend the rest of your day at this website. I've had, well that's Jack describing sampling this rock from the floor of this crater. Now because of his experience in prior missions, he knew that young craters would have glass covered floors. And his thought was that if we could sample a rock from the floor of this crater, one of these craters that's very young that hasn't been disturbed, we may be able to measure the magnetic field of the moon in those samples because theoretically, those fragments, those rocks on the floor of the crater haven't been disturbed, haven't moved since the crater formed. So if you know exactly the orientation of the sample as it was the moment the crater formed and then a million years later when he came along and sampled it and put it in the lab, he put it exactly in the same orientation, you could measure any paleo old magnetic field. So he went through some painstaking efforts not only to find the right crater, to sample it, and bring it back and preserve it. And he did that. It was brought back, analyzed, but essentially largely forgotten. He went off on a world tour, he went back and analyzed the samples, but never really revisited the sample and never did that really detailed documentation of trying to reposition exactly where that sample came from. So one of the coauthors of this paper took it upon himself to do that. Now this is that first image he describes taking where he knows he has the lunar module precisely located in the image, the sample came from right here. And then using basically some very simple reconstruction techniques we can identify features in the image. And this is a blow up of this image here. It's hard to see, but basically it's a before and after that lets us show exactly where that sample came form in the floor of this crater. Now tying these features, we've got the lunar module, these craters and boulders sitting on the surface. There's the tracks of the rover in the image there. This is the LROC image. There's the lunar module. There's feature A, B, C, and D. We can precisely locate, just using trigonometry that I thought in high school I'd never need to use again, and find exactly where he was on the surface when he sampled that crater and exactly which crater that came from. It was never determined exactly, there's a lot of craters. But we were able to say exactly where that sample came from and now a series of at least proposals are under way to try and get the money to be able to analyze that sample in the way that Jack saw fit. It's very elegant, very simple, but essentially allows us to precisely know. And actually an important thing I mentioned, the topography of the moon being as well understood as it is: we now know where features are on the lunar surface. Especially around the lunar modules, within centimeters. Further away from the lunar modules, a few meters. But we have a precise, genetic grid. We know where features are on the lunar surface to a degree that we've really never known for any planetary body apart from the Earth before. And the last point I wanted to make is about these sculptured hills. This is, again, out of an airplane window view. Here is the North and south maseefs, here's that Lee-Lincoln scarp, the landslide, there's where they landed. And this is the sculptured hills. And perhaps you can start bleeding when you see this knobby texture versus this more coherent texture, and you can pair the sculptured hills to the South maseef. And so the third and final EVA went to the North and East up along the base of the North maseef, two stations where large boulders were identified and finally to the bottom of the sculptured hills to sample that material at station eight and then finally make their way back to the lunar module. Jack, my coauthor for the talk, described a little bit about what they did. [inaudible] >> Noah Petro: So there's Jack who's scampered, almost the right word, up 30 meters uphill, not easy, to get this one rock of the whole area that he sees that's unusual. And what you hear him do is just the best example of field geology on the moon. He's telling Gene, all these rocks around here are the same. Get one of these things. Not going to worry about it, but that rock up the hill there, that's what I want. >> A minute to make up some of this time we've spent at station 6 and 7-- >> Noah Petro: Oh come on. Come on. Mute. Ha ha. Awesome field geology, this field site happens to be on the moon. He's telling Gene, get one of these samples. I'm going to go up and get that one. That's unusual, that doesn't look like these other things. That's what we want to get. He goes up, he documents it, images it, then he starts trying to kick it to roll it downhill and it goes down a little bit. Because he knew that that was the unusual sample and potentially would be from the sculptured hills. But as I showed in that documentation and really for decades, it was never thought we were able to get materials from the sculptured hills. That rock that Jack is doing an excellent job of documenting, was unusual. It was unlike other sample-- let me go forward one. It was unlike-- I could play that video. It's just so awesome. Unlike other samples, there was no visible [inaudible] In fact if I had let Jack talk more which I probably should have done, he says there's no boulder. We don't know where it came from. That boulder was unlike any of the other boulders they samples over at station 6 or 7. This is an LROC view of these boulders. Here's the close up view. They went here and sampled this and you can see the little trail of the boulder which goes up the mountain. Station seven boulder. They actually didn't see the boulder trail when they were on the surface here, only with these images are we able to see oh yes, station seven boulder came from further up the hill. So that's one other area where the new data has really helped in the analysis. But the boulder from station eight had no context. And I said before, context is king. But we pulled in another data set. A compositional data set that came from a mission just before LRO. An Indian mission that had on it an instrument that I was fortunate enough to work on. The Moon Minerology Mapper. And this psychedelic on the right-hand side here is basically a color map-- a compositional map. And colors indicate variations in composition, specifically minerology. And in the North massif which is here, basically we see apart from a few examples, it's largely [inaudible] which is the kind of average composition of the lunar surface, of the lunar crust. The sculptured hills is a much more polka dot pattern of different colors, suggesting that it's much more compositionally diverse and indeed, the composition of that boulder that was sampled at station eight, matches almost identically the composition that we can infer of the uphill portion of that mountain. So that tells us that indeed, it did sample sculptured hills material and has led to a whole different understanding of what this material represents. Our current hypothesis is that, remember I mentioned earlier that they wanted to go as far from the embrium basin as possible? It turns out that there's a chance that this material is actually objected from that large basin. Maybe we didn't get ejecta from tycho but we may have gotten ejecta from the embrium basin in the form of the sculptured hills. And this material will be very deep material ejected by that basin over about a thousand kilometers from the Apollo 17 landing site and brought here about 3.8 billion years ago. So it turns out that, again, some of this new data tells us as much as they thought. Maybe they weren't able to sample the sculptured hills. By golly, they did. And again, you saw that example of Jack doing what geologists do best which is observe, classify very quickly, and find the outlier. The geologist, you always want to hang out with the geologist. They're going to find the best restaurant that nobody goes to or the best bar that nobody goes to because there's one thing that geologists don't like to do is wait in line. So new light on the Taurus-Littrow Valley and the Apollo 17 landing site. One, it appears that tycho may not have caused that avalanche. That we may actually not have an accurately aged the tycho crater event. We have located the exact source and orientation of this precious sample, 70019. And that indeed the sculptured hills were sampled at station eight in the form of that boulder which suggests that the sculptured hills have a very complex and convoluted origin that involved a basin 1,000 kilometers away. Ok, so Apollo 17. Still crazy after all these years. I'm going to elave you with just a few thoughts. We have a lot left to learn about the moon. We have not, in any way, closed the book on our understanding of the moon. We have many future missions that we'd like to explore. I'm involved with a group that's proposing or will propose a mission to sample from the far side of the moon. We have a successful current mission at the moon that's healthy and happy, and of course we have the wealth of past missions: robotic and human, that we're still learning from. Apollo has left an incredible legacy that we are still unraveling and understanding. As much as these are events that happened 44 and more years ago, they're still as relevant today and still as important to our understanding of the moon. And this is perhaps masybe the least important statement but maybe also the most important statement that I'll make today, is the solar system is amazing. All of the planets tell us something about how planets in our solar system and indeed in all of the other solar systems in the galaxy work. And the moon is one of our best opportunities to understand the processes that shape all these solid bodies. With that, I'll thank you for your time and your attention. Two minutes over. Not bad for me. And thank you for your time today. [applause] >> Michelle Cadoree Bradley: Please, if you'd like to start with any questions and we see a number of hands raised. So why don't we go from bottom to top. [inaudible] >> Noah Petro: So Apollo, so yes, the question was Apollo's 18, 19, and 20 were originally missions that were going to happen. Actually Jack Schmidt was going to be the lunar module pilot on Apollo 18 and got bumped up to 17 when 18 was cancelled. And so the question, if I hear you correctly, is the equipment that was built for those three missions still usable-- oh. >> Not equipment. Whatever the mission you're looking for geologically on the moon, are those missions that cannot be fulfilled in the 18, 19, going to replicated in some fashion with what you're doing now or? >> Noah Petro: Ok, yes,. So basically the landing sites or the objectives of those missions, are those still viable today? Yeah, absolutely. Apollo, and those missions were cancelled early enough along that they didn't get into the incredibly detailed ok, we're going to land here and sample these places and there were a number of possible landing sites that were identified for those missions. I'd say the story has almost gotten more complicated because now we know that there are many more places we'd want to go. But certainly those landing sites which would've been a Copernicus crater, there are several lava or magnetic features or volcanic features that were identified. There are amongst many possible future landing sites. The geologists are also sometimes greedy. We don't want to just go back-- I mean, if we could go back to one spot that would be great. But you know, one place isn't going to answer all the questions. So, but certainly the work that was done then is relevant. It's actually one of the things in my limited amount of time in working for NASA and Jim might share this thought, it NASA is really good at a lot of things but one of them is making reports. And so every decade or so there is another report. And this is not intended to criticize anybody, it's important to revisit it. But there are a number of ok, here are the five most important things that we can do in the next ten years and every ten years we brush that off. But those landing sites would still be amongst many high priority spots. >> You said that the experiments were cancelled after five years. Why? >> Noah Petro: That's, ok. Money, basically. The [inaudible] program has active experiments going on from the Apollo. Ultimately, each of the missions left something behind but the long lived ones were at Apollo's 12, 14, 15, 16, and 17. And those were terminated on September 30th, 1977. Now for those of you in the civil service or work for the government, September 30th is the end of the fiscal year. And they were turned off because it was costing a million dollars a year to operate those experiments. There was also a concern at the Johnson Space Center, there's a room that was used to basically, you know, the 1977 equivalent of a server farm. Basically the station where the room, maybe as large as this room, that was used to get the data, process it, and then archive it, was valuable real estate at JSC. And they were getting ready for the deorbit of Skylab which was one of the later Apollo missions, upper stage of the Saturn five that was used as our first space station. Again, the engineering model, the training model is there at the space museum. And so that room, the folks that were concerned about bringing Skylab down safely, they wanted space to be able to do that. And so that was another argument that was used to terminate [inaudible] was that they needed the room. They wanted that room. So it's ultimately those two things that conspired against the right word while I said it. So that basically acted to terminate the [inaudible] program prematurely. Some of the equipment was failing but there was still very important seismic date, there was still information to be learned. But a million dollars a year was deemed needed to go elsewhere. So it was terminated. Apollo 17's operated again for that five years but you had Apollo 12 that had been running since 1969 so in some cases it was seven or more years of almost continuous data coming down from the moon. There was a question on the, yep. [inaudible] >> Noah Petro: Yeah I can go back to-- let me see. Yeah, I mean this was as if you were there. It's good. For some people I don't want to strap to the side of a rocket. Nobody in this room. This is not sped up, certainly I didn't do any monkeying around with this. It goes very fast. And remember, this is going, well the Saturn Five when it cleared the tower three or four seconds after launch was going 60 miles an hour. That's pretty slow when you think about it. I can go-- I've got CRV and I can go faster than that in three seconds. Not that I ever would though. But you know, this is a lighter rocket and it clears the cloud deck, it was not a very cloudy day that day but it was cloudy enough, within a few seconds. But it takes-- actually, if you go back and watch the launch of New Horizons to Pluto, I mean that cleared the moon in a couple hours. Six hours or less. Because that thing had to get going fast. We only had to get to the moon so we didn't have to go that fast. But launching rockets is awesome. We'll go back and then come back. [inaudible] >> Noah Petro: Ok. Yeah, so that's a great question. And actually, the origin and age of the moon is really important because, that's again the big question. We still argue about that. But indeed, the samples, even from the very first mission Apollo 11, showed us that the moon was very old. And under, most likely underwent a global melting event early in its history. And so early on, a model was developed that hypothesized that about four and a half billion years ago, an object about the size of Mars struck the Earth and sent into orbit around the moon, basically for lack of a more technical term, a bunch of debris. But ejecta from the Earth that coalesced, reheated, and melted to form the lunar crust and mantel. And so samples from subsequent missions show that the crust of the moon is about 4.4 billion years old and so a more detailed analysis has gone back and showed when some of that would have actually coalesced. But on the Earth, there are some very few places, Northern Canada, Central Australia, where you can get rocks that are upwards of 3.8 billion years old. But those are few and far between. Whereas the crust of the moon has these rocks pretty much, I won't say everywhere, but widespread rocks that are 4.3 or older billion years old. And there's still arguments about the age of the moon. We know that it's likely older than 4.4 billon years, but there's a lot of that early history in the solar system that we don't very well understand. But the record for those rocks is sitting on the moon and likely not sitting here on the Earth. So we just went through staging, that was the bright flash there. And in a moment, you'll see the space crust separation if you're worried about it. Fortunately we know LRO survives, so anything you see here couldn't have been too bad. [inaudible] >> Noah Petro: Yeah, so the question is about some recent work and it's very good to see a lot of effort going back into reanalyzing and asking these questions. It's not a closed question of the early dynamics of where the moon came from. And really, the more we learn about the moon-- that the moon has water in it, that it's not completely dried out, punches some holes into the theory of this large impact early on because one of the ideas was this early impact will devolatilize whatever came to form the moon very quickly. Well we know the moon has volatiles in it so I'd say it's still open to debate and question and I would say again, perhaps a little self-serving that more analysis of these Apollo samples, there are some Apollo samples that have never been analyzed. There's some samples that haven't been analyzed in 45 years. So I think we have a lot left to learn from those samples and looking towards what that tells us about day one from the moon. Moving down the line. Yep. [inaudible] >> Noah Petro: Well, that's a great question because I'm going to speak for myself. It's all I know. I certainly feel like I missed out on that opportunity to participate for something like that and hopefully, I'm not that old but I know there's an end to my career somewhere and hopefully between here and there there's something that I could contribute. I think when we are ready to go back to the moon as a species, we can do so safely with the data that we have here. So yeah, I feel like I missed out but there's a lot of great things that are going on here. You know, we lost our way, we got-- there was a war going on. I wasn't there. And looking at and talking to folks, there was a certain sense of, even Apollo 12 wasn't as popular as Apollo 11. The second time humans go to the moon wasn't like-- by Apollo 13 people were barely paying attention. I think that tells u more about how we have to. I mean, we've learned a lot in the last year about how our, and when I say our I mean the U.S., the attention span and the interest of the country. So whenever we are ready to do something bibg, and going to the moon was big. Billions and billions of dollars spent to do it. Society, leadership has to be on board to continue it. We talked about turning off [inaudible] after five years or prematurely. We have to be on board with big investments. And the investment that was made in Apollo has told us about the origin of the moon. Again indeed, events are happening four and a half billion years ago. These are things that can't be solved for the price of this cup of coffee. Even if it is from Starbucks. You can't do it. >> Michelle Cadoree Bradley: We have time for one more question. >> Noah Petro: Ok. There's a question in the front here. Yeah. [inaudible] >> Noah Petro: Sure. So this is radiation doses. So the question is, what do we know would happen and the causes and events of a solar flare. As I mentioned, one of the instruments on LRO is this radiation detector. Unfortunately, the moon, the sun has been fairly quiet the time that we've been at the moon with LRO for the last seven years, so we haven't had one of these large solar flares occur. But we know that if not lethal, a harmful does of radiation. Now where would they go? If we're on the moon for a long period of time we we want to be able to get the astronauts to sagety. Now whether or not that shelter is in their habitat that's covered in some thickness of [inaudible] that would protect them, shield them, one of the surprising discoveries and I don't have an image of it. So I'll just put a picture of Mt. Marilyn up for a moment. Is that there are places that we've seen that are pits. They're collapsed lava tubes. We don't know if the pit is the size of the hole or a little big larger, or if there's an extensive lava tube system. We've seen these scattered across the lunar surface. Mostly in areas of volcanism. Those could be good habitats, because now of course you have to get into it so you have to go down into a pit that's 30, 40, 50 meters deep. That's not easy. You saw the astronauts running around, climbing up and down a rope ladder that's going to be next to impossible for an astronaut on the surface but there may be some natural shelters that we found on the moon that would prove to be potential if they're extensive enough to be shelters for astronauts. The other possibility, though, is just designing a habitat that has enough shielding. Or again, if you can take the loose material on the surface and cover that, that could provide enough protection. Humans have remained in lower-Earth orbit since 1972, and when you're in lower-Earth orbit you're in protection of the Earth's magnetic field. So if we want to go on to Mars, this is going to be a major issue for any long duration deep space exploration, will be radiation hazards. But instruments like crater and instruments that are on Mars right now measuring radiation, we at least know the expected doses. This provides some arguments of whether or not this means you should send people who are young and can agree that if this is going to happen this is going to happen, or if you send older people. No offense. Who don't have to worry about having kids or anything like that. Everybody's got their own vested interests. But it's definitely going to be one of the major, although achievable, but a major hurdle for long duration deep space exploration. >> Michelle Cadoree Bradley: Dr. Petro, thank you very much, we have so enjoyed this presentation. If you have questions, perhaps you can come outwards and down and talk with Dr. Petro. >> Noah Petro: Absolutely. [applause] >> Noah Petro: Thank you very much! >> This has been a presentation of the Library of Congress. Visit us at LOC.gov.