>> From the Library of Congress in Washington, D.C. ^M00:00:04 ^M00:00:22 >> Stephanie Marcus: I'm Stephanie Marcus from the Science, Technology, and Business division here at the Library. I want to welcome you to Cassini's Grand Finale. It sounds sort of like a symphonic piece, and it probably is with a loud crash at the end. Let's see. We are really lucky to have one of the Cassini team members here today. So close to Cassini's demise which will be a week from Friday, the 15th. Conor Nixon is a space scientist from NASA Goddard. He is originally from Belfast and was educated in the UK. He is, he was, he earned a BA in Natural Sciences from the University of Cambridge. A Master of Science in Radio Astronomy from the University of Manchester. And finally his PhD in Planetary Science from the University of Oxford. He's been with the Cassini message, mission since his graduate days, and he is a, he's had many awards at NASA. The latest was the Robert H Goddard Award for Exceptional Achievement in Science. We have 13 years of Cassini observations, highlights, and the grand finale to get through. So please help me welcome Conor Nixon to the Library. ^M00:01:45 [ Applause ] ^M00:01:51 >> Conor Nixon: Thank you, Stephanie, for such a gracious introduction. And thank you for the invitation to come here. I'm really excited to be here at the Library of Congress. My first time in this building. And to address you all and convey the excitement that I have for this mission that I've worked on for more than 20 years. It's now coming to a dramatic end. I'm sure some of you have heard next week this is coming up really fast. So today I just want to talk about some of the exciting highlights that we've had from the mission so far. It's been a great voyage of discovery. And then take you right up to the present day and talk about what we've done in the last few months and weeks. And what's going to happen in the next eight days. ^M00:02:34 ^M00:02:38 So first thing I just want to introduce Cassini. So Cassini is actually the Cassini, we call it the Cassini-Huygens mission. It's actually two spacecraft and they're - one was produced by NASA. This is the Cassini orbiter. Which is currently in orbit around Saturn. And then there was a probe which was built by the European Space Agency named Huygens. This was named after a Dutch scientist who was the discoverer of the giant moon of Saturn called Titan. And this was attached to Cassini. Shortly after it arrived in the Saturn system, the end of 2004, it was released and this became the first probe to land on the moon, Titan. And that gave us a whole different insight into what was going on on Titan. That mission was short in duration. It was just a two-and-a-half hour descent to the surface. And then that probe, the Huygens probe, its batteries were used up. But since then the Cassini orbiter has continued with its 12 instruments to give us the science that we've had. ^M00:03:44 ^M00:03:47 So how did Cassini get to Saturn? This was launched back in 1997. And the Cassini spacecraft was so big that we couldn't just push it on a direct trajectory all the way to Saturn. So we had to use a trick. And the trick that we used was to get a slingshot from some of the inner planets. So Cassini actually flew by Venus a couple times, by the Earth. And then finally it ringed its way out to Jupiter and got its final slingshot maneuver to give it that extra boost, that extra kick to get it all the way out to Saturn. So after a seven-year cruise, Cassini reached Saturn in July 1st, 2004. And then it burned its rocket engines for about 70 minutes. And it braked and slowed itself down so it could go into orbiter around Saturn and begin its voyage around Saturn and the moons. On the way of course we were able to get glimpses of Venus and Jupiter. And this proved to be very useful for us because we were actually able to test out all our systems. And we got a lot of great science actually out of Jupiter as well. This was the launch. It was almost 20 years ago. And it was a fantastic launch. It was a night launch. I was lucky enough to be there. I was still a student at the time but it was a really exciting time to wish Cassini well on its way. And then as you can see, seven years later, it burned its rockets to go into orbit at Saturn. So the Cassini mission was originally designed to have a four-year lifetime from 2004 to 2008. But 2008 came around, the spacecraft was still in robust good health. Every system was working. We still had half our fuel left, so we continued the mission for two more years to see the equinox at Saturn. Then at that point, we were extended for another seven years to go all the way to 2017. And this was calculated to be the end of the mission when we've used up all our fuel. And there's nothing left in the tanks. So we have to end the mission at that point. And this has been really great because as you can see in this graphic here, Saturn has very long seasons. So Saturn takes 30 years to go around the sun. And so it's 30 times as long as the year that we have. And that means that its seasons are about seven-and-a-half Earth years in length. So just to see one season, you have to be there for seven-and-a-half years. Well, Cassini has been in orbit for 13 years, so that's almost two full seasons. And that's given us the chance to see the spring and the fall reverse between the Northern and the Southern hemisphereon Saturn and also its moons. So here's where we are today. We're right at the end. And I really love this graphic. There's a lot of information packed in here. And this really summarizes what we've done in the entire mission. So at the top, you can see the orbits that we've had. The shape of the orbits. As Cassini has gone from more of an equatorial orbit of Saturn to more of a polar orbit. The orbits have tilted up and down so that we can see different things. The, the large yellow circles you see up at the top half are these Titan flybys. So these are flybys of Saturn's largest moon, Titan. And then below that you can see flybys of Enceladus. A moon which I'm going to talk about. And some of the other [inaudible] satellites. Saturn has 62 known satellites at last count. And Cassini has discovered several of those new one. So a lot of, a lot of satellites ranging from very large. Titan's the largest, 5000 kilometers in size. Down to very small ones, just a couple of kilometers. And at the bottom here, you can see the seasons changing in the Northern hemispherefrom winter to spring and now to summer. And right over on the very right-hand, sorry. Right around the very right-hand side, you can see these, I don't know if I can use my pointer. But here you can see these what we call our final orbits. So we have 22 of three final orbits, and we're right now approaching our very last orbit. ^M00:07:53 Just some great facts and figures here. I'm not going to talk about all of these. But Cassini's traveled billions of miles. And the thing that I find the most exciting is the number of scientific publications, nearly 4000 at the time this was written, scientific publications have come out of this mission. So it's really been a fantastic mission. So I'm going to start by showing you a few highlights of the, of the Cassini mission during the 13 years that we've had. I'm going to begin with one of Saturn's smaller moons, and this is Enceladus. This is 500 kilometers in, in size. Or three hundred miles. This is what the moon Enceladus looks like. It's named after one of the Titans from mythology as some of its sibling moons are. And you can see that Enceladus, it's a very bright object. It's not covered in sand or dirt. It looks like an icy material. It's one of the brightest, most reflective objects we have in the solar system, almost looks like a billiard ball. And if you look towards the bottom of the image here, you'll see these blue cracks on the surface here. And there are four of these long streaks or cracks. And Cassini has been, Cassini caught the very first view of these cracks. And shortly afterwards, we were able to discover something very dramatic about Enceladus. So as Cassini flew by Enceladus, we discovered that it was disturbing Saturn's magnetic field. And you could see here in this image that these magnetic field lines which should be shooting right past Enceladus were being deflected. And this was an indication that something was going on here. And in fact, when Cassini turned its heat-sensing cameras on Enceladus, we could see that these cracks which appeared to be these blue streaks in the, to the visible cameras were in fact glowing [inaudible] heat that were tens of, of degrees warmer than the cold, cold background. So this was a really exciting indication that there was something unique about the [inaudible] polar area of Enceladus. ^M00:10:12 ^M00:10:16 When Cassini turned its cameras back toward the sun, we were finally able to see what was really going on here. In fact, these cracks on the South pole of Enceladus are shooting material out into space like fountains or geysers. Just like Old Faithful. Some people on the project like to call these a Cold Faithful. So because unlike the, the Earth, of course this material is much colder. It's, we believe it's water that is shooting out into space. But it's instantly turned into ice crystals. These are shooting for tens or hundreds of miles out into space all the time. So you can see looking back towards the sun, these jets which are not easily visible. You can see them with the sunlight reflecting through them. So this is showing us that Enceladus is one of the very few places in the solar system that's actually an active, geologically active world. And we're very excited to discover this and to find out some more about what's going on here. ^M00:11:18 ^M00:11:22 So just some other images of the plumes here. We can see that these four, four predominant plumes are tracing out the four cracks that we have on the South pole. So what do we think is going on here? It appears that there's liquid water buried somewhere inside Enceladus. And this moon is kept from freezing solid into a block of ice by the tidal forces that are, that are kind of kneading it like a ball of dough by Saturn itself. So as the moon goes around Saturn in its elliptical orbit, it experiences stressed and compression and tension which keep, keep it warm inside and allow the water to remain liquid under the surface. And of course the surface on the outside is frozen solid. But there's enough water inside, and there's enough pressure that periodically, as the moon goes around Saturn, it's venting water out into space. And this is turning into these geysers that we see. So here you can see tiny little black dot right in the middle. This is Enceladus. And what's going on here, it's, it's actually creating its own ring as it goes around Saturn. And this is what we call the E ring, E for Enceladus. And it's, it's trailing all this ice material behind it. You can see here that it's actually making a kind of a wake, like a darker wake where it's plowed through its own ring. So as it repeatedly goes around Saturn, it creates what we call a [inaudible] or basically a donut or icy material. And this is spreading out in all directions. And as it comes back around, it's actually making like a wake as it plows back through its own material. And these jets are shooting material out in all directions. And you can actually see some of these jets which are shooting the material out. Some of the material goes ahead of Enceladus. It speeds up as it goes towards Saturn. And some of it trails further behind. So Enceladus is really this little 500-kilometer-size moon is creating a cloud that's bigger than Saturn itself. ^M00:13:36 ^M00:13:40 So another look inside Enceladus here. This is what we think is going on inside. We think that it's a, a rocky core, but then it's surrounded by this blue layer. You can see indicated here which is where the liquid water is. And on top of this we have the ice shell. Now this is exciting not just as a natural geological phenomenon. This could be potentially even more exciting than that. Because on the Earth, we know that at the bottom of the sea bed, right where the volcanic vents are in the Mid-Atlantic Ridges, there's a lot of life which actually likes to congregate there. And if the core of Enceladus is indeed warm, and it's surrounded by this liquid ocean, this could actually be a similar environment. And this is really exciting because this gives the potential that there could have been life evolved here inside Enceladus. This is the deep ocean, Mid-Atlantic Ridges on the Earth. You can see here that these are geologically active. And these create a whole ecosystem of life surrounding these. And right now we can't see that far down inside Enceladus. All we have to see is these plumes of material which are shooting out into space. But this is kind of like a free sample and Cassini has been able to fly repeatedly through these plumes. First, we didn't go too close. But eventually we got down to just going a few tens of miles above the surface and shooting the spacecraft through these curtains of material. And using an instrument onboard Cassini to actually measure the material. And we found some really fascinating things about the material. That it's not just water. In fact, it contains organic substances, methane and ethane molecules. There's also salt containing potassium and sodium grains. And there's even larger organic pieces. So there's now a huge amount of excitement that's been generated by Cassini to say, "Let's go back to Enceladus someday. Let's send another mission." But with different instruments this time. We'll have instruments that can actually go through these plumes and maybe look for any evidence of life. Any traces of biological material which Cassini was never designed to find. Because we didn't, we did not have any clue that we were going to find these jets. So this is like a, a free sample from the interior which is shooting out into space. And in fact, Enceladus is not the only moon either that has liquid water inside. Cassini has now shown evidence that all four of these larger moons of Saturn are warm enough and close enough to Saturn that they've maintained a water layer inside. Including Titan, which I'm going to talk about shortly. Mimas, we nicknamed this one the Death Star for obvious reasons. It's got that, that look to it; that mean look to it. And Dione which is one of the other inner moons. And we believe that all these moons have a liquid water layer inside. And, and who knows what's going on inside. So this is really exciting that we've discovered what we call these ocean worlds in the outer solar system. And these may now be our best chance of life outside the Earth. So Titan is Saturn's largest moon. I've already alluded to this. And this was a really exciting [inaudible] to discover. We had the Huygens probe which descended to the surface in January 2005. But it wasn't until later that year that we were able to make some of the most dramatic discoveries. And in fact, something that was long suspected but we never had the chance to look at before given its thick, hazy atmosphere. Was that there's material that's raining down on the surface. In fact, Titan is the only moon in the solar system that has an atmosphere, a substantial atmosphere. We have planets that have atmospheres, but Titan is the only moon that has an atmosphere. All the other moons appear, just you can see all the way to the surface. And on, and on Titan's atmosphere, the action of sunlight acting on its methane atmosphere, creates complex molecules. And in the colder polar regions, these are actually condensing and raining down onto the surface. So this is rainfall, but not as we have on the Earth. Not water rainfall. This is methane rainfall. And Cassini was the first to see these lakes and seas on the north pole of Titan. So this, these are remarkable. These lakes and seas are about the same size as the Great Lakes that we have in North America. So this largest lake is comparable in size to Lake Superior and this is containing billions of gallons of hydrocarbons of methane and ethane. So these would be like your liquid natural gas. Just seas of this material. ^M00:18:26 Cassini also discovered that Titan has dune fields near the equator. But again, these dune fields are not the sand dunes that we would see on the Earth made up of silicate material. These are dune fields made up of little organic, dried-up organic pieces kind of like, almost like miniature chips, chips of plastic. This, this would be like Titan's atmosphere creating a smog, and organic smog somewhat similar to the, the smogs that are created by vehicle fumes on the Earth. We have these, you know, famous Los Angeles smogs. And Titan's doing something similar but in a natural way. And these little particles are coming down on the surface. And then they're getting blown around by the winds and creating thousands of miles of dune fields. Again, organic material, but this, this time not liquid, [inaudible] solid. Titan has some small mountains. Possibly some of these are actively volcanic. It's difficult for us to tell because of this thick atmosphere. And of course clouds. And when the Huygens probe was able to descend to the surface, land on the surface, it could see that there was dried up rivers and seas. That showed us that maybe these organic lakes and seas had been more extensive in the past. And now they had retreated towards the polar regions. But in the past, they may have encompassed the entire planet or much of the, the lower latitudes. And when these first pictures came back, this is actually from the surface. This, this image here is from the surface of Titan. There's a little icy boulders that are maybe just a few inches or tens of inches in size. And when these first pictures came back, the first reaction out of the jet propulsion laboratory was, "Have we mixed this up with Mars? Because this looks like Mars." But this really was the surface of Titan. And these little boulders are not rocks as they would be on the surface of Mars. But these are icy, icy boulders. You can see here the magnificent imagery that the Huygens probe was able to take. As it floated down, serenely down to the surface over a couple of hours. Actually getting, getting, getting lower and lower here from 150 kilometers. You can't see anything. You're still in the haze. And then as you descend 30 kilometers, 8 kilometers, 1.5 kilometers and down to a few hundred meters. You can see this magnificent vista never seen before of this moon. Back in 1980, the Voyager spacecraft flew by but wasn't able to see the surface. Didn't have the right cameras onboard. But finally we're able to see the surface and see these mountains and carved river channels on the surface of Titan. So Titan is the only place other than the Earth that you could go to and actually have rainfall. All the, like I said, all the other moons, none of them really have substantial atmospheres. Some may be active. [Inaudible] for example, has active volcanology, but it doesn't have an atmosphere. So Titan's the only place that has a cycle of evaporation, rainfall, and liquids on the surface where you really could just go, if you had a spacesuit, you could go and float around on a boat on the surface of Titan. You could take, you could take a voyage across one of its lakes. And you know, so who knows what the future holds for tourism. ^M00:22:00 In that respect. This is one of my favorite images of Titan here. This was looking back towards the sun. and this shows you for real. You can see the glint here of the sun reflecting off one of the, one of the lakes. And I like to tie this together with another world that we're more familiar with. Which is the Earth. You can see that these two bodies, like I said, are the only two places in the solar system that actually have liquids on the surface in the form of lakes and seas. So Titan and the Earth are in some ways very distant cousins. And the exciting thing about Titan is because its atmosphere is, has such great similarities to the Earth but also differences. For example, there's no oxygen. There's no life that we can see. But it may be similar to the Earth several billion years ago when the Earth had newly formed, and its atmosphere was really different. Before the rise of plants that were able to breathe the oxygen into the atmosphere that we now have. The atmosphere of the Earth may have been much more filled with carbon dioxide and methane. And in fact so Titan may be like a time machine that we can go back a couple of billion years to the early Earth and see what would have been happening in those processes. Titan things have just happened so much more slowly because it's so much colder. And further from the sun. So now I want to come on to Saturn. Of course this is our, this is our main guy here in the center of the Saturn system. Such an amazing planet. Many people's personal favorite planet in terms of just the drama of the, of the ring system. And here, it's a shame we can't have our [inaudible] lights down a little bit. But I hope you can see that there's actually something going on here on Saturn's Northern Hemisphere. And this was in fact a huge storm which erupted in 2010. And Cassini was there for a ringside, literally a ringside seat to see this going off. And this storm erupted. And these have been seen in the past from the Earth, but of course, much further away. And this storm erupted, and it gradually erupted all the way around the planet. We called this the Dragon Storm because of its initial appearance. And in fact eventually due to the winds that gusted this material so that it wrapped all the way around the planet. It was like the dragon's head was eating its own tail. And this was really phenomenal. Cassini was able to watch this unfold over several months. Typically these storms occur on Saturn about every 30 years. This one came about ten years early. So Cassini was very lucky to be there for its, for its ringside seat to see the storm going off. You can see here as well the, the sun is projecting the shadow of the rings onto the planet. So the sun would be slightly off to the, to the North here, projecting through the rings and onto the planet here. So as this storm erupted, Cassini was able to look using its different cameras to look into longer and longer wavelengths. You can see here, as we see longer wavelengths, we can see deeper into the atmosphere. And in fact the, the instrument that I work on is the longer wavelength infrared camera on Cassini. And we look at heat. And we were able to see that this storm was glowing 100 degrees brighter than the background of Saturn. ^M00:25:33 So this was a huge warm spot. And this was just throwing off energy that was visible to Cassini here. ^M00:25:45 ^M00:25:49 So Saturn's North pole has even more remarkable stories to tell. If we, if we were able to look right down on Saturn's North pole as Cassini can, this is what we would see. And you see this remarkable ship emerging here. This was just glimpsed by Voyager as it flew by. But Cassini was able to really show us the first picture looking down on Saturn's North pole. And this is what we call the Hexagon for obvious reasons. This is a wind jet which is circling around Saturn's North pole. You can see here in the center. This is actually a hurricane eye wall, something very topical. This week, with all the drama going on in the Caribbean Sea. This hurricane on Saturn's North pole, this eye wall is many times bigger than the ones that we have on the Earth. In fact, this circular region here would take up about the entire Easter United States. So this is, this is much bigger. And this entire hexagon shape is about twice, two and a half times the size of the Earth. So this is really huge. And, and the winds that are going around here are the fastest that are known in the, in the entire solar system, 300 kilometers an hour. So really fast wind jets here. In fact, people in the Cassini mission are still working to unravel exactly how this six-sided shape emerges. But what we do know is this is a jet stream which is similar to the jet streams we have on the Earth. And as it, as it goes around the pole, it wavers from side to side. Creating this six-sided structure. ^M00:27:30 ^M00:27:34 So let, let's take a look at Saturn's rings. Of course, these are one of the most dramatic features of Saturn. And here's a, a, a primer to the rings. You can see here the, the brightest, thickest part of the ring's what you call the B ring. And that's sandwiched on either side by the A and the C ring. These were named a long time ago by early astronomers. There's a prominent gap here, the Cassini Division, that was discovered back in the, the 1600s from some of the earliest telescopes. And you can see here, there's another gap here, an A ring called the [inaudible] Gap. And we now know that there are in fact moons that are going around inside the rings that are carving out these channels. And all the way down here, you can see the innermost D ring, a very faint ring which stretches almost down to the surface of Saturn itself. We'll talk about that a little more later. ^M00:28:32 ^M00:28:36 So here's a view of the moon Pan. This is one of the close-up views that we just got recently. Going around inside that, that [inaudible] Gap which I just showed you. And so as Pan goes around, it's able to clear the material in the rings. And you know Cassini's cameras have for the first time been able to show up close up what these moons look like. ^M00:28:59 ^M00:29:03 Another really fabulous view here. You can see that these rings, even though these are almost incredibly thin, just a few tens of yards thick. Even though they're hundreds of thousands of miles in diameter. There are places where the material gets disrupted by the moons that are going around. And throws off these clouds. So you can see these sort of pillars of material. And you can actually see the shadows that they're throwing onto the rings here. And these are being thrown up for tens, tens of kilometers above the rings. And then they're casting a shadow here. You can see from the, from the sun. ^M00:29:40 ^M00:29:46 So this is the outermost edge of the main rings here. This is the [inaudible] which I just showed you which has the small moon, Pan, going around in here. And then right outside the main rings, we have this ribbon which we call the [inaudible]. And this ribbon is maintained actually by a pair of moons which go around either side, and we call those the Shepherds. So one is going around just inside the, the [inaudible]. And the one on the outside you can see, actually this little guy right here. And as they go around again, they're able to, to cause some disruption to the, to the [inaudible] as they circle Saturn. So when Cassini was, was taking movies of the rings, we were able to see even more structure here. You can see these, we call these spokes or these shadows or spokes in the rings. They look almost like the spokes you have on a bicycle. And these are dynamical phenomena again which are caused by [inaudible] from the gravity of the, of the various moons going around. But there's a lot of work still to be done to understand exactly how these disturbances occur. Which cause these periodic thinning and thickening of Saturn's rings. ^M00:31:05 ^M00:31:09 So Cassini's remarkable 13-year mission is now coming to its last few days. So let's, let's go right up to date and look at the activities that are planned for the end of the mission. So during the solstice part of the mission which was began in 2010. And it's taken us up to the present day. This shows you the orbits which Cassini has, has made of Saturn. And Saturn of course has its, has its rings. And these are tipped over by 27 degrees compared to Saturn's path around the sun. so Cassini has for most of its time remained in this same plane as the rings. But of course if we, and that's where the moons are, in fact. So the Saturn system is like a giant, you know, it's like a giant saucer. And many of the moons are going around in the same plane as the rings. So to encounter those moons, Cassini has to go around in that direction. But to see the rings then of course we have to change our orientation. So then we tip our orbits to go over Saturn's poles. And then we can actually look down and see the rings. So over the last seven years, these are the orbits that Cassini has made around Saturn. You can see right in the middle here, periodically going from the, the equatorial orbits to the polar orbits so that we can see different things. And changing our, changing our path each time to encounter many of these distant moons. A lot of these orbits were redesigned after we discovered those remarkable jets or geysers coming out of Enceladus. So that we could go back for another look and another look and another look. And eventually we went by 22 times. Just to, just to keep looking and to sample the material in different ways. ^M00:32:57 ^M00:33:01 And here highlighted in yellow, you can see these are the final orbits. So when we first arrived at Saturn, we stayed well away from the rings because these rings are chips of ice mostly that are circulating around. But who knows the damage they could do to the spacecraft if we flew through the rings at you know ten miles per second. This could cause a lot of damage to the spacecraft. But as the mission is drawing to a close, we've really decided to go for, go for broke and do, do more dramatic things. So the first maneuver that we did starting in December of last year was to take our innermost orbit much closer to Saturn than we'd ever gone before. In fact, just to graze the very outer edges of the main rings. And in fact to go right by this F ring, the one that I just showed you like a ribbon. And to take a really close look up at the F ring and the moons there. And that took us through to April of this year. And then beginning in April, for the last five months of the mission, we decided to do something even more dramatic. Which was to take a dive right between the innermost ring and the planet itself. And this is a gap just a couple thousand kilometers wide. And these are what we call our proximal orbits Cassini [inaudible]. And it's coming up to its 22nd orbit right now. And these are just six-day-long orbits. So you can see here again, we had these what we called the ring-grazing orbits where we went around and grazed the outside of the F ring and went around from December of last year through to April. And then we did an encounter again with Titan. Titan's what we frequently use to give us a little kick, like a little change in our trajectory. And then to come into these really dramatic, what we call proximal orbits, actually diving through the gap between the planet and the rings itself. And originally, we were planning to do maybe a dozen of these. But then we thought, "Well, how many can we squeeze out of it, right?" We don't want this to end. So we went up to 15 and then 18 and then finally the mission chief engineer said, "Okay, you can have 22 and that's it. That, that's really the limit." Your, our fuel tank is, is well into the empty zone. Where our "check fuel" light is on. We're down to less than three percent of our fuel. The margin of error is five percent. So. So, we're really running on fumes right now, but we're confident that we can just finish, finish the mission out. So you can see here in close up just how dramatic it is diving through this gap between this innermost, there's a faint D ring here which stretches down. And then just a couple of thousand kilometers where it empties out. And in fact, it's not even really ever completely empty. So in fact, those innermost ring particles, as they get closer and closer to Saturn, and then receive the reflected sunlight off Saturn, they actually begin to melt and turn into just water vapor or mist. So Cassini's diving through a cloud of mist as it goes through this gap every time. It's really like going through a car wash every time it goes through this gap. And at the start we were using our main dish antennae as a protective, almost like a bulldozer to go in front of us as we went through the, the rings. But as we were got more confidence that this material's not going to damage us, we were able to turn the spacecraft and do different pictures which I'll show you as we, as we went through. So here you can see this is the surface of Saturn here at the bottom. And then as you go outwards you go through the rings. So this shows you all the way out through the rings. These were the orbits that started in December of 2016. You can see each one of these little blue dots indicating how close we went to the outer rings. And you can see, here's the F ring here. And then all the way, and then starting in April 22nd, we did our, our kick with Titan. And we flung Cassini right into this gap. And you can see we jumped right down here. So we're now right down, right above the surface of Titan, or of Saturn just dramatically doing these 22 orbits here. And you can see this, this last one here doesn't look too good because this is a, this is inside the atmosphere. And that's coming up really, really soon. So I want to show you some of the, some of the latest images that we have during these last few months of the mission. Here is a tiny little moon, Daphnis, shown here for the first time making waves as it passes through one of these little narrow tracks that it's making. You know, the [inaudible] gap in the outer edge of the A ring. Someone had a great meme online, if you go and look it up that says, you know, "You know, you may be small, but you can still make waves." And it is a really, really great meme. You can go look it up online. So Daphnis doesn't care that it's tiny compared to Saturn. It's still making itself, its presence known. ^M00:38:28 And here you can see February 2017 as we were doing our, our F ring orbits. One of the first looks-down on the North pole of Saturn as it emerged finally in the sunlight for the first time. This had been in darkness during the start of the mission. But we were finally able to look on in full color. You can see this hexagon shape here which I mentioned here. This is 20,000 miles across, and in the center, we have this really remarkable, glowing-blue hurricane system here which is 1000 miles across. ^M00:39:12 ^M00:39:16 And one of the fascinating things is that this, this hurricane on Saturn's North pole has actually changed color. You can see here back in June of 2013, the entire region looked, had a bluish tinge to it. While the center was more of a, of a greeny-orange color. And then this is reversed. So this shows us that the action of, of sunlight is actually changing the, the, the particles in the atmosphere. And causing them to, ultraviolet light from the sun is causing them to change color. Here's a look at Titan from May of this year. One of the things that we've been looking for as Titan's North pole went into summer was that there'd be more evaporation, right? So the sunlight hits these methane lakes and there'd be more evaporation. We'd start to see clouds forming and, and rain. And it took a long time. Titan kept us waiting, but finally in May of 2017, we were able to see these really dramatic clouds streaking around Saturn's North pole. Here you can see these lakes, these methane-rich lakes on the surface. And these clouds, these are methane clouds which are going to rain methane back down on the surface. ^M00:40:30 ^M00:40:34 And just when we thought that Cassini has no more surprises, that we'd been in orbit for 13 years, what is there left to discover? We've seen the plumes of Enceladus, we got a close look up at some of these tiny innermost ring, ring moons of Saturn. And low and behold, they look like pieces of pasta. I mean, take your pick tortellini or flying saucer. And so these moons which are just you know ten miles across, have this remarkable shape. In fact, they look almost like a miniature Saturn, right? They have their, their own, it looks like they're, they've got their own little flattened ring around them. But this is, is, is stuck on. This is, it's almost like a tutu skirt you know that you would have that's stuck on to these moons. And it's, it's maybe a couple of hundred yards, couple hundred meters in, in thickness. So it's quite, quite strong, quite stable. And this is a coalesced material. So it's [inaudible] or a collected ring, ring chips [inaudible] collected around the equator of these small moons. They've just all coalesced and stuck together and you know melted and refrozen. And formed this almost like a solid ring around it. So nobody had predicted this at all until, until we were able to take these images. So really unbelievable. ^M00:42:03 ^M00:42:06 So what I have here is a, a little, short movie clip. This was taken back in April when we did our first close dive over the North pole of Saturn and our first dive going right down over Saturn and down to the, down to the rings. And the cameras were turned towards Saturn. So Cassini was basically taking a, taking an image strip looking over the North pole and coming down and down. And then right before we got to the rings, we had to turn our cameras away so that we could put our antennae in the forward direction as we passed through the rings for the first time for safety. So we go almost to the equator and then stop. So let me show you this, this movie clip here. So this is Cassini flying over the north pole of Saturn. You can see here, here's the, this hurricane eye wall storm. These images are all in black and white. You can see these other little storm vortices as we passed on. Over the hexagon, over the outer rim of the hexagon, and then begin to go down across the plane. You can see here we're going over these, these streaks through the - all the way to the hexagon are going down over the Northern Hemisphere. And these were at the time the closest images that had ever been taken of Saturn. So we're going from about 40,000 miles away at the North pole down to just about 4000 miles. As we come right down, you can see all the structure of Saturn's storms here. And the image track gets narrower and narrower as it gets on towards the bottom. ^M00:43:51 ^M00:43:57 So even more, more than nine years after the mission was originally designed to finish back in 2008, Cassini was still giving us first of a kind science. It was almost like having a new mission all over again. So you can see here. ^M00:44:19 ^M00:44:28 So here something even more fantastic in many ways. This is looking at the rings from the inside looking outwards across the rings. So this was taken on August 20th. Cassini for the first time actually kept its cameras going all the way through as a dive between the rings. And it turned its cameras outwards, and what you see here is looking at the rings. And then as they go thinner and thinner, you're actually just looking at the ring's edge on from the inside looking out. This is a place that no spacecraft had ever ventured before Cassini did it. And the fact that we are able to do this seems you know almost miraculous. That spacecraft is still surviving, still returning these miraculous images. So just some of the amazing facts and figures here. You can look up online for Cassini's Grand Finale. So I'm, I'm almost finished. I want to just show you a couple of fun cartoons. And I'm going to finish with a short video sequence, and then I'll take your questions. So many people have been really motivated by the Cassini mission. In fact, if you go online and look on, on, on the web and look on Facebook and Twitter and all these social media [inaudible] you'll see some of the imagery. People have done their own artwork. They've done cartoons, and this is one of the fun cartoons that came up online. So Saturn's saying, "Hey, Cassini, I hear you're retiring in September 2017. Congrats! How do you want to celebrate? Maybe do lunch with me and my moons or something?" And Cassini says, "No, I'll just go barreling straight into your atmosphere, learning as much as I'm, as I can before I'm crushed to death and vaporized in a spectacular whirling inferno beneath your mysterious stormy clouds," ^M00:46:25 [ Laughter ] ^M00:46:33 It was like, are you for real? It's like, whoa! That's awesome. So you know, no, no retirement for Cassini. He's going to keep working right up to the end. So back in the springtime, the jet propulsion laboratory out in California, one of the branches of NASA created a really nice video sequence which I want to show you here. It's a bit of a tear-jerker. People were, there was, when it was shown to the mission scientists, there wasn't a dry eye in the house. So I'm going to show that to you right now. This is just a few minutes in length. And I hope you'll have sound as well. ^M00:47:18 ^M00:47:22 [ Music ] ^M00:47:24 >> A lone explorer on a mission to reveal the grandeur of Saturn, its rings and moons. ^M00:47:33 [ Music ] ^M00:47:38 After 20 years in space, NASA's Cassini space probe is running out of fuel. And so to protect the moons of Saturn that could have conditions suitable for life, a spectacular end has been planned for this long-lived traveler from Earth. ^M00:47:57 [ Music ] ^M00:48:00 >> Five, four, three, two, one. And liftoff of the Cassini spacecraft on a [inaudible] to Saturn. ^M00:48:11 [ Inaudible ] ^M00:48:17 >> In 2004, following a seven-year journey through the solar system, Cassini arrived at Saturn. ^M00:48:26 [ Inaudible ] ^M00:48:29 The spacecraft carried a passenger, the European Huygens probe, the first human-made object to land on a world in the distant outer solar system. For over a decade, Cassini has shared the wonders of Saturn and its family of icy moons. Taking us to astounding worlds where methane rivers run to a methane sea. Where jets of ice and gas are blasting material into space from the liquid water ocean that might harbor the ingredients for life. And Saturn, a journey [inaudible] ruled by raging storms and delicate harmonies of gravity. ^M00:49:15 [ Music ] ^M00:49:18 Now Cassini has one last daring assignment. ^M00:49:24 [ Music ] ^M00:49:31 Cassini's grand finale is a brand-new adventure. Twenty-two dives through the space between Saturn and its rings. As it repeatedly braves this unexplored region, Cassini seeks new insights about the origins of the rings and the nature of the planet's interior, closer to Saturn than ever before. ^M00:50:00 [ Music ] ^M00:50:06 On the final orbit, Cassini will plunge into Saturn, fighting to keep its antennae pointed at Earth as it transmits its farewell. In the skies of Saturn, the journey ends. As Cassini becomes part of the planet itself. ^M00:50:32 [ Music ] ^M00:50:54 >> So there you go. ^M00:50:55 [ Applause ] ^M00:51:03 >> Stephanie Marcus: That was grand. We can take questions now. And if you would repeat the question so that everyone can hear it. >> Conor Nixon: Of course. >> Stephanie Marcus: And anybody who has to leave, too bad. >> Conor Nixon: And, and please take the materials outside. There's some stickers and bookmarks and things from the Cassini project. So you're welcome >> Stephanie Marcus: Help yourselves and take for friends. >> Conor Nixon: Okay? ^M00:51:25 [ Inaudible Question ] ^M00:51:33 So Saturn really is, is all atmosphere. It doesn't have a surface the way what we call the inner planets like Venus and Earth and Mars have a surface. So the atmosphere, it's like Jupiter. It's a big ball of gas unless you go deeper and deeper into the atmosphere. The gas would eventually turn into a liquid. And then right in the center we believe that it's, it's got some weird state of hydrogen where it's like a metal, and then there's probably some rock in the very center. But this storm, it, it, it comes from deep within. We don't know the mechanism right now that's creating it. But like I said, every 30 years or so there's enough energy that gets stored inside. One of the theories is that it's energy that is trapped by water clouds. And eventually, this energy gets stored inside until eventually it erupts. And it breaks through the clouds that have been trapping the energy inside. And then it erupts and creates this giant storm. Then it all begins again. The clouds, the deep water clouds reform, and they trap the heat inside again. Yes? ^M00:52:40 [ Inaudible Question ] ^M00:53:17 Okay, so the question was about the [inaudible] and there's two parts to the question. And Cassini's a plutonium radioactively-powered spacecraft. Do we have enough plutonium being produced for future missions? And the second part was how do we feel about the plutonium being deposited into Saturn. So you know, for the first part of the question, traditionally NASA spacecraft into the outer solar system have all been nuclear powered. The Voyager spacecraft, nuclear powered. Both Galileo mission to Jupiter in the '90s and Cassini were nuclear powered. So they have a few tens of kilograms of plutonium which are generating heat. And this generates electricity. As far as future missions goes, right now there's a debate about how much do we need, plutonium? And one of the things is [inaudible] improvements in solar technology. It's [inaudible] for some of the applications that we've formerly used plutonium we're now ambitious enough to think that we can use solar power. So in fact the next mission that's going back to Jupiter, the [inaudible] is actually designed to use solar panels. Very, very large and highly efficient new generation solar panels instead of plutonium. But for other applications, we still need plutonium. So in fact the Rover, which is on Mars right now there's this Rover Curiosity, originally called the Mars Science Laboratory which is about the size of a small car that's trucking around on the surface of Gale Crater trucking up a mountain. That is nuclear powered, and you couldn't imagine having big enough solar panels that would do that, do that mission. The previous smaller Rovers, of course, Spirit and Opportunity were solar powered. But for missions, for example, some of the missions that have been proposed have been, "Let's actually go float a boat on the surface of one of these Titan lakes." Now at that level, you're so far down in the clouds that you're not going to get enough solar energy. Especially not with a small object that can't deploy big solar panels. There's even been ideas, in fact there's a mission just been proposed to NASA for one of its recent competitions that would fly a helicopter on Titan, actually a quadcopter that would be again, about the size of a small car and this is nuclear powered. So we do need the plutonium for those missions. As far as Cassini's plutonium going into Saturn, you know, Saturn is, you know, it's 80 times the, the, the mass of the Earth. The plutonium and radioactive elements that are on the Earth are just a small part of the Earth. So this is just going to be you know a few atoms amongst trillions and trillions of atoms. It's not going to make any difference to Saturn itself. Yeah. Okay. Yeah, at the back of the room? ^M00:56:10 [ Inaudible Question ] ^M00:56:17 Right, so the question was any fear that the boats or other missions we propose would contaminate with organic material? So in fact, NASA has someone down in NASA headquarters really close to here on the south side of the mall whose job is called Planetary Protection. And it's not just protecting the Earth from asteroids. It's actually protecting the other planets from us. And missions now that go, go out to Mars and to the other planets, our whole view has changed compared to what we were doing in the 1970s. Instead of just sending things out there, we're now very rigorous about not wanting to, not send little gift packages from the Earth of microbes or bacteria which then might colonize another pristine environment. And then we wouldn't find out what we're trying to find out which is has life evolved there itself? Is it different from the Earth? You know, if we go there and find a bunch of Earth microbes, that's not going to be helpful. In fact, that's the reason why the Cassini mission is plunging into Saturn. It's to protect some of the moons from anything that might still be remaining on Cassini, any microbes that might still have somehow miraculously survived this 20-year mission. We don't want to have Cassini crash into Enceladus or Titan where there might be, there might be something going on. And future missions, we're going to take [inaudible] protections. So those missions that have been proposed, there was a boat proposed for Titan a few years ago. The quadcopter, as I mentioned, those will have to undergo a very rigorous [inaudible] protection. There's also a study underway right now for a, a mission that might land on Europa, which is one of Jupiter's moons. Which also almost certainly has an ocean inside. And that would land, maybe drill, take some ice cores. And that's going to have very, very rigorous planetary protection on it. Yes? ^M00:58:08 [ Inaudible Question ] ^M00:58:20 Yeah, I wish I could - so the question was, is the yellow color of Titan for real? And I wish I could have spent more time talking about Titan's, it's actually my favorite object in the solar system. It's what I do most of my own research on. Because it's, it's, it appears just like this orange ball. In fact, if you were to look through a telescope from, from the Earth. If you had a decent size backyard telescope, maybe a 12-inch telescope, you could actually see this little orange dot right beside Saturn. And, so it is orange. It's really orange. In fact, this is what really confounded scientists for literally centuries. So when Titan was first discovered, it was called Titan for a reason. And it's because it was thought to be the biggest moon. And it turns out it was playing tricks on us. It's not the biggest moon. It's because it's got a big, puffed-up atmosphere which is - it actually stretches about 1000 kilometers away from the surface. Because it's got a low gravity, the atmosphere can, can stretch out. But the, the orange cloud layers that we see are two or three hundred miles above the actual surface. So when scientists measured the size of this dot, they got it wrong because they weren't seeing the surface. And it wasn't until the Voyager spacecraft went by in 1980. It used its radio dish to send back a signal to the Earth. And as we watched for when that signal got blocked by the surface, we were finally able to determine the true size of Titan. And it's just slightly smaller than one of Jupiter's moons, Ganymede, by about 70 kilometers. But it's really close to - you know, and that's why it's called Titan. But the, the orange color is produced by the action of sunlight on its atmosphere which is methane. And as the sunlight strikes the methane, it breaks up the, the molecule which is carbon and hydrogen, and is reassembles it into chains. And these chains form these smog materials. And the smog is the orange material that we see. There's a little bit of nitrogen mixed in there as well. So actually the atmosphere would be pretty poisonous. It's got a lot of carbon, nitrogen molecules in there which we call cyanides. And those are not healthy things to be ingesting. So you've got a, you've got a waft of, of [inaudible] probably if you were down on the surface of Titan. So it, the orange smog is the, is the atmosphere. And it really is an orange color, yeah. ^M01:00:36 [ Inaudible Question ] ^M01:00:56 That's a really great question. So the question is isn't Enceladus the only moon that's shooting geysers out into space? Also are they only shooting out of these four cracks? So back in 1989 when Voyager II flew by Neptune, it was able to see some geysers on one of Neptune's moons, Triton. These are much smaller in size than what's going on with Enceladus. But we were able to see some, some vents on Triton. More recently there's been a lot of attention focused on Europa, moon of Jupiter. And even though we had a spacecraft there in the '90s and early 2000s called Galileo, the spacecraft had some technical problems, and it wasn't able to get as much data back as we'd originally hoped. The environment around Jupiter's actually very, very harsh radiation environment. It really, it really just chewed up that spacecraft really quickly. But since then in the last couple of years, there's been some indications that there may be similar plumes coming from, from Europa actually. Which is a similar moon to, to Enceladus. Although it's about seven times wider. Right now those observations viewed with the Hubble Telescope really tenuous. You know, we're just seeing maybe, just a hint of something. So we're really not sure. There's actually a lot of telescopes observing Europa right now to try and find out if there's, if we can get a better detection of that. But Enceladus is really unique in the sense that it is small, and it's got these really dramatic jets which we can just see every time we fly by Enceladus. We can see these jets. They appear to be coming predominantly out of these four cracks. But the curious thing is that there's other cracks around Enceladus in other parts that are not active today. So what we think is that maybe in the past, the moon just kind of flipped over. So maybe the south pole was, you know is now the equator, and the equator's now the south pole. So there were cracks before that were active. But then as the moon has turned on its side, it's created new cracks. And the old ones have, have closed up. So we can see cracks all over the surface that may have been active in the past. But right now it's the ones on the south pole that appear to be where all the energy is concentrated. ^M01:03:07 ^M01:03:10 Okay, question here? ^M01:03:11 [ Inaudible Question ] ^M01:03:26 Another good question. The question is what have we learned about the formation of Saturn's rings? So Saturn you know originally we thought Saturn was the only one of the four planets that had rings because they're so dramatic and so obvious from Earth. Like I said, you can look with a backyard telescope and you can see Saturn's rings. And it's a wonderful thing to do. But as the voyager spacecraft went out, they found that actually Jupiter, Uranus, and Neptune all have very, very faint rings. But their rings are different. Their rings are, are dark material. They're like dust rings. Where Saturn's rings are bright, icy, and they're big. So there's several theories. It appears that Saturn's rings are young. And that's why they're still there because they're not really stable. Over many hundreds of millions of years, they would eventually either evaporate. Or they would spiral inwards to the planet and they would go away. It may be that Jupiter, the rings that we see of Jupiter and Neptune and Uranus, those faint, dusty rings leftover. Those may be kind of remnants of rings that were more big and bright and icy in the past. That have just left kind of a faint trace now. There's theories that maybe Saturn's rings were created fairly recently by the, by the breakup of a satellite. So it may be that there were, there were more satellites than we see today. And two of them, you know, they banged into each other. Broke up, and just stretched this debris ring which has been stable for maybe tens of millions of years or hundreds of millions of years. But probably not going all the way back billions of years to the start of the solar system. So it may be a transient phenomenon that we're just seeing this ring now. And if we were around in another, you know, few hundred million years, you know, they wouldn't be there. So, so that's, that's one of the theories. But one of the, one of the many scientific things Cassini's doing right now, this dive between the [inaudible] rings is not just purely to get some great pictures. Actually, we can measure the deflection of the spacecraft by the gravity. Not only the planet's but by the gravity of the ring material. So we can use that to actually weigh the rings. And get a better estimate of how much mass of material's in there. And that's going to give us a better estimate as to how young they are. So that, that's, that's just going on right now, you know, as we speak. Exciting. >> Stephanie Marcus: Do you have any idea what time of day the demise is going to be? >> Conor Nixon: Yes, thank you for reminding me of that. So next Friday, it will be just before 8 a.m. I believe on the East Coast. It will be just before 5 a.m. out in California, where I'll be out at the jet propulsion laboratory. The signal from Cassini takes about 83 minutes to get back at the speed of light back to the Earth. So the times that we're recording is the time the signal is at the Earth. .The spacecraft, when the signal stops on the Earth, the spacecraft will have died 83 minutes earlier. So what Cassini's going to do is it's going to keep its, its main antennae pointed to the Earth for as long as possible. And you saw like right at the end there when it's fighting with the thrusters to try and keep its altitude control, it's going to try to keep its antennae pointed to the Earth. As long as possible. Eventually the atmosphere is going to be dense enough that it's going to cause the spacecraft to tumble. And then it will lose altitude control. That's when the signal will be lost. And then a few tens of seconds after that, it's just going to be like a meteorite or a meteor. It's just going to - pieces are going to start flying off. And it's going to, it's going to burn up 30,000 miles an hour in Saturn's atmosphere. >> Stephanie Marcus: You'll probably have to have a wake, right? >> Conor Nixon: We have several events planned, yeah. For next, next Friday, yeah. Everybody's going to be getting up really early in California. They'll go down to - California's [inaudible] Technology's hosting a big event for about 4000 people. Everybody's who's ever worked on the mission's going to show up. ^M01:07:11 [ Inaudible ] ^M01:07:14 >> Stephanie Marcus: Well, I guess we should end and get out of the room. [Applause] >> Conor Nixon: Yes. >> This has been a presentation of the Library of Congress. Visit us at loc.com.