 but I'd like to introduce our guest speaker. Our guest speaker is Dr. Linda Spoker. She's a NASA research scientist at the Propulsion Laboratory in Pasadena, California. She is currently the Cassini Project Scientist and a co-investigator on the Cassini Composite Infrared Spectrometer team and has worked on Cassini since 1988. Since joining JPL almost 40 years ago, she's worked on the Voyager Project, the Cassini Project, in conducted independent research on the origin and evolution of planetary brain systems. She also supports concept studies for new missions to the outer planets. She enjoys playing the piano, reading, and hiking in national parks, including her favorite park, Yosemite, it's wine too. She's married, has three daughters, and five grandchildren. So please welcome Dr. Linda Spoker. I'm very happy to be here. And with that, let me go ahead and get started with my presentation. I have a lot of wonderful things to share. First, I just want to point out that the room behind me is the mission support area. And it was 12 years ago that we watched Saturn orbit insertion from that very room. Now let's see what's Cassini been up to since that time. So if you look, my first slide is one of my very favorite images of Cassini. This slide shows basically a backlit Saturn. It shows what Saturn looks like and the rings with Saturn covering up the sun. And we took 141 images, put them together into this very beautiful mosaic. You can see not only the main rings that you'd ordinarily see through a telescope, but you can also get a really wonderful view all the way out to Saturn's E-ring. And if you look carefully, you'll notice that there's a bright ring all around Saturn. And Saturn is refracting the light from the sun since the sun is behind Saturn. And in that, you're seeing every sunrise and every sunset on Saturn. A lot of times I get asked the question, why do we explore space? And there are some grand science questions that we address in our exploration. And one of those is the question, are we alone in the universe? Has perhaps life originated elsewhere beyond the Earth? And if it did, how did it look like? How did life originate on the Earth itself? So we're looking for life around other places as well. Another one of the grand science questions is how did the solar system and the Earth within it come to be? How is it evolving and where is it headed? And this shows the planets in our solar system, the asteroid belt, and of course, Saturn. Saturn is the sixth planet out from the sun. It's about 30 times further from the sun than the Earth. Now, Saturn is one of the two gas giant planets, Jupiter being the other, the largest planet in our solar system. And if you were to compare their sizes, what you see here is the Earth and the Moon and the distance between them to scale. The planet Saturn itself is a giant gas ball. If the Earth were a tiny marble, it would hold up to 764 Earths inside of it. And this whole system, including the rings, is very expansive. You can see it would just fit in between the Earth and the Moon. And very beautiful as well. This is an overview of the Cassini mission. It shows the 30-year orbit of Saturn about the sun. Cassini was launched in 1997. We had Flyby's Gravity Assist, Flyby's Two of Venus, one of the Earth, one of Jupiter, and then arriving at Saturn in July 2004. It shows our mission phases. We have a prime mission. And at four years long, a two-year Equinox mission where you observe the planet in the rings with the sun edge onto the rings. And we're now in a seven-year Solstice mission. And that mission will end in September 2017 and the Saturn Northern Summer Solstice itself is actually in May of 2017. And you can see a green box and some very special orbits at the end of the mission. And toward the end of my talk, I'll talk in more detail about the new things we expect to learn in this very unique set of orbits. Right now, the Cassini spacecraft is going up in inclination. We're getting very close to that green box. In fact, last Thursday marked the one-year marker from one year from the end of the mission. And so we're getting close to that final year. And we're ending the mission because Cassini is running low on fuel. Essentially, the fuel light is on for Cassini. This is another view or an overview of the mission. This is by calendar year. The top bar, you see each of the orbits for Cassini. The number of orbits we use Titan to shape those orbits. By the end of the mission, we'll have flown by Saturn's moon Titan 127 times. And so that's a lot using its gravity to shape our orbits. In the prime mission, we had just three flybys of Enceladus. But Enceladus turned out to be such a fascinating and such an incredible world that we then added 20 more flybys of Enceladus through the mission. And we had our last Enceladus flyby in October. We've had 15 very close flybys of some of the other icy moons in the Saturn system. The very bottom panel shows the seasons changing. We arrived about two years after Northern winter and the mission will end just a few months after Saturn's Northern summer solstice. And then of course, at the very end, there are those 22 very special orbits for Cassini where we dive actually in between the innermost ring and the top of Saturn's atmosphere before ending the mission. Now onto some of the science highlights that I'm gonna cover. It's just really a handful of them. Cassini has been a tremendously successful mission. Some of the things that we've discovered include, and I'm gonna cover Enceladus, a little bit about Titan, quite a bit about the rings themselves. I think the rings are very, very exciting targets and then go on to Titan and also talk about then the end of mission too. So this is Enceladus. Enceladus is a tiny moon. It's only about 500 kilometers across about one seventh the size of our moon. And we knew from Voyager over in the early 1980s that Enceladus was very bright. If you look carefully, you'll notice that at the South Pole of Enceladus, you really have no craters and the surface is very bright and very lightly cratered, more heavily cratered as you go toward the North. And the light bright colored surface as well as the absence of craters told us that Enceladus was very, very young. What we noticed in looking at Enceladus's South Pole is a series of four linear, what we nicknamed tiger stripes. These are fractures in the crust of Enceladus at the South Pole. When Voyager flew by through the Saturn system Enceladus's South Pole is in darkness. So we didn't have a chance to see these very intriguing features. We initially knew something unusual was going on with Enceladus in 2005 with our first close flyby of Enceladus. We came within a thousand kilometers. And what we noticed with the magnetic field instrument is that instead of the magnetic field lines going down to the surface of Enceladus, it looked like they were wrapping around the South Pole and something that was very reminiscent of a comet. And so the magnetometer team requested that we go closer. And so on the next flyby, we came within 175 kilometers of Enceladus and we made some remarkable discoveries. The first of those is the fact that the Enceladus South Pole is hot. Here's that you can see a temperature map on your left where blue is the coldest and as you go up to the reds and even the yellows, the temperatures climb higher and higher. And this excess of heat correlated in particular with those long linear tiger stripe features. So it appeared there's excess heat coming out of these tectonic fractures on the surface of Enceladus. Here's a blow up of one of those tiger stripes. It's about two kilometers wide on average. They're about 130 kilometers long. You can almost see what looks like frost on one edge of the tiger stripes. And what we found when we looked more carefully, looking basically now in a backlit view that there was material actually coming out. There were over a hundred individual jets shooting water vapor and water ice particles into space. Here's another view of some of those jets. They go on to form a large plume of material and that plume contains not only just water vapor and water ice particles, but in measuring their composition, we have instruments that can basically sniff and taste. The material coming out of Enceladus is plume. What we see is not only is there water, but there's also carbon dioxide, methane, ammonia. You have carbon, hydrogen, oxygen, nitrogen. You have many of the key ingredients that you would find in life. Here's another view, another one of my favorite images. This is again a backlit view. You can see the Terminator, the shadow line on Enceladus, and even across the shadow line. You can see evidence of these jets as they go high enough to reach their icy fingers out above the shadow. Here's a picture that I took. This is a fountain in France in the Versailles Garden. And this fountain is named Enceladus. And Enceladus was one of the giants and he got into a dispute with Athena, which he lost. So he was condemned forever to remain underneath Mount Etna. And so this is just so amazing, this fountain that was built in the 1670s. And here, this Enceladus fountain is showing a jet of material similar to what you would see on the icy moon and all of this. This is an artist's concept of what the gas and icy grains might look like coming up from the water reservoir. We now know there's a liquid water ocean underneath the icy crust. That ice is maybe about six miles thick at the South Pole and maybe 10 or 12 miles deep. What we think is that there's carbon dioxide in that. You can imagine shaking up a champagne bottle and that carbon dioxide gas for helps force that water and that water vapor up through the opening and on into space. That water vapor is what lofts the tiny icy particles. We can make measurements of those. We've found salts, sodium and potassium. They tell us that the ocean is salty and has a very similar pH to the ocean here on the earth. We also know that some of the tiniest grains escape Enceladus in this view that any god is Enceladus. You can see the stream of material coming out and you can see that there's a room of material coming out of Enceladus. I think somebody might want to mute. I think I hear dishes or something in the kitchen. That's you. Yeah, it might be you, Rachel. Sorry, I'll mute it. And so there's the material coming out from Enceladus going onto a former ring that fills in the orbit around Enceladus. Here's another artist concept. This is a view of the global ocean that's underneath Enceladus's icy crust. Another thing that we discovered is that not only do you have these jets coming out from the surface of Enceladus, but there's evidence of hydrothermal vents coming out of the rocky core of Enceladus. There's a rocky core, the global ocean, and then the ice shell around Enceladus. What we found in the particles are they're tiny grains of silica, nanosilica grains that could only form in water that's very close to the boiling point. And so we think that water goes into the core of Enceladus. It's heated and when it comes out, it forms these hydrothermal vents and those tiny particles of silica crystallize as they hit the cold water and then they can come out of the jets coming out of Enceladus. So very interesting and intriguing. And in fact, you have now a number of factors that make it plausible that life might exist there. You have a global salty ocean, similar in salt content to the Earth's ocean. It's long lived, it's global, so we think it probably has been there since Enceladus formed. You have organics in the plume, long chain carbon, hydrocarbons that we can actually measure. In both the gas and the particles, the excess heat energy and now the hydrothermal vents on the ocean seafloor. And if we look by analogy, this is along a mid-oceanic ridge in the Atlantic Ocean and this is on the Earth and we can see evidence of water called white smokers and the similar kind of thing happens here. The minerals and the hot water that's coming from underneath the surface, the water comes out, the minerals crystallize and you get what looks like smoke. And what's intriguing is these ocean vents deep in the ocean where no sunlight can penetrate, you find an amazing array of life. You find tiny crabs, two worms, life on many scales in very close to this source of heat and energy and nutrients and we believe we have very similar conditions on Enceladus. So who would have guessed when the Cassini mission launched and we had our chance to go and fly close to Enceladus that we would find a world so far from the Earth that might be a place that's a habitat for life here in our own solar system. With that I'd like to move on to Titan. This was the view that the two voyagers had of Titan. Basically a haze in shrouded world, this haze is much like the smog you might find in a bad day in Los Angeles. Basically we couldn't see through the haze with the voyager cameras or the voyager instruments. And so in the 1980s, not long after the voyager flybys, scientists got together and said we need to go back to Saturn. And in particular, we want to learn more about this moon Titan. Titan has basically a nitrogen rich atmosphere. It's about the size of the planet Mercury. Had Titan formed anywhere else in the solar system, it would have been a planet in its own right. And within that atmosphere of nitrogen, there are hydrocarbons and it looks a lot perhaps like the early Earth may have looked like. Prebiotic chemistry, but at just temperatures much, much colder than we have here on the Earth. So already in the 1980s, plans were put in place to go back to the Saturn system. And it was a joint mission for NASA and ESA. And in this case, the European Space Agency or ESA provided the Huygens probe. This is an artist concept of the probe. Cassini carried the probe and then dropped it off on its way by Titan and actually recorded the signal and the data coming back from Huygens. On the far left, you can see the probe plummeting into the atmosphere. It's heat shield slowing it down enough so that a parachute could deploy. At that point, the heat shield has dropped and the Huygens probe continued on to land on the surface of Titan. We didn't know what we would find. Would we find a world with a global ocean of methane on its surface? What would we find when we landed? It was so fascinating to be part of watching those first pictures come back. And here were some of those views. We had not only a camera, but instruments to measure the pressure, temperature and composition of the atmosphere. We know on Titan that methane plays the role that water plays here on the Earth. It can be a liquid. It can be a gas and form clouds or it could even be a solid. So here's the Huygens view. The haze cleared about 60 kilometers altitude and we got better and better views of the surface until finally here we are landing on the surface and actually sending data back for another half hour to Cassini. It took about two and a half hours underneath the parachute to reach the surface of Titan. And then the probe sent back another half hour of data before Cassini was over the horizon and could no longer pick up the data. If you look at the image on your left, there's about a hundred icy pebbles there. They're rounded indications that fluid is flowing on the surface of Titan. You can see the horizon, the time of day is about 10 minutes after sunset. And you can see that image also in color. In the color image, you see a bright spot. The Huygens probe carried a lamp. We wanted to be able to see the true color of the surface by having a lamp of known specular intensity to look at it. Just for comparison, you can see on the right next to it, you can see the Apollo footprint and off in the distance, the astronaut sitting next to the flag and sort of the similar view that Huygens probe saw. On the far right, you see that the Huygens probe saw what looked like river channels flowing into what looked like a dry lake bed. And it's in this dry lake bed that the Huygens probe landed. A little bit more about Titan. It's a very alien world, but it looks hauntingly familiar. And here's an example of one of the lakes and seas on Titan. This is like GMRA. It's about one and a half times greater than Lake Superior here on the earth. And it's filled with liquid methane. And you can see the river channels flowing into it. We also saw evidence of sand dunes that the methane is broken apart in the upper atmosphere, forms longer and longer chain hydrocarbons. Those hydrocarbons fall to the surface and the equatorial region of Titan is full of these long linear dark dunes. Also mountains in this view, this is a view color coded with the height. This mountain also looks like there's some kind of a flow coming out of it. Perhaps a cryovolcano in the distant past flowing out on the surface of Titan. Also, here's an et and false color, one of the methane clouds. And finally, once again, landing in one of the dry river beds on Titan. Now the image on your far left isn't a camera image. It's actually a radar image that we used radar to pierce through the haze on Titan and get these remarkably detailed views. And as are the view of the dunes, those are from radar data rather than from the imaging data. Now this is a view from the cameras of Titan. We carried this time methane filters and with the methane filters we can look through and see features on the surface of Titan. One of the things we wondered early on is was that material, that flat dark material that we saw in the radar images, was it truly a liquid or a tar-like material or something else going on? And we had a very unique opportunity. This is looking in the near infrared again at five microns to actually see a specular reflection. That's where sunlight comes in at a certain angle, reflects off the surface at the same angle and went back into the spectrometer on Cassini. And we could then definitively say that to get a specular reflection like this, you need a liquid. Now the specular reflections are interesting because we have models that as the seasons change as we go toward Northern Summer that perhaps waves will start to come up on the seas of Titan. And the specular reflections will change if you have a specular reflection over choppy water versus still water, still methane. So we're looking to see if there are any changes in our specular reflections that might tell us something about the winds that are blowing across the North Pole on Titan. This is another close-up view. If you look at those small white circles, we were able to probe the depth of the lakes. They're on order about 150 meters. We also were able to probe the depth in some of the canyons, very deep canyons, steep sided, maybe 40 degrees of an angle. And in particular, it was so intriguing, it's further away from the lake. The level, the surface level of the methane was about tens of meters higher, telling us that indeed this material is flowing into the lakes. Now I wanna say some more about Saturn's rings. They're one of my favorite targets and talk a little bit more in detail about just what we've learned with Cassini. First of all, the main rings have very simple names, basically A through G. The main rings you can see through a telescope are A, B, C, and D. The Cassini division is also there as well as the Anki gap. And in each of these major gaps in the rings, there's a tiny moon. The Cassini division holds pan and the Anki gap contains daftness. There's a narrow F ring just to the outside of the main rings. And as you go further away, you encounter a ring, the G ring. There's actually a tiny moon that's the source of these particles. And then of course, the E ring where Enceladus is at the thickest part of the E ring. And the E ring actually goes into the main rings and all the way out to the moon Titan. So there's a lot of material supplied by the icy plumes of Enceladus. Here's a Cassini image of the rings. You can see they're slightly different colors. The B ring is the most optically thick and the most massive. And you look at the C ring and D ring, the end A ring, they look grayer and these rings have less material. And so micrometeoride pollution works more effectively when you have less ring particles and we think perhaps causing the darkening that you see. What exactly causes that golden color of the rings we're not sure? We have some ideas that could perhaps be nano grains of iron, perhaps silica, perhaps solans coming from Titan, lots of ideas. And a Cassini's end of mission will actually be able to sample some of these particles and measure their composition directly. So I'm really looking forward to that. If you look at the rings on the, that was the sunlit side. This is the side that you normally see through a telescope. If you look at the dark side of the ring, you'll notice that the B ring now, the sunlight is not able to penetrate through the thickest part of the B ring. The Cassini division becomes very bright as does the C ring. These more tenuous rings allow sunlight to come through and the A ring is brighter as well. This is a movie that Cassini made as we basically went through the ring plane. Starting out on the sunlit side of the rings, you can see the Cassini division and inky gap and that bright ring on the right is the B ring. Every once in a while, you'll see a tiny moon go screwing by. There's Titan, Titan is going by. And then as you get to the other, the dark side of the rings, now the B ring is quite dark. And you can see the Cassini division has brightened considerably and the A ring is bright. And you can just see a hint of the very bright C ring at the far right of the image and there goes Titan again coming out the other side. So we spent several hours putting together that particular movie. Now Saturn's rings are interesting in another way in that they're less than meets the eye. We know that the B ring is the most optically thick of the rings. It's maybe 10 times more opaque than its neighboring A ring. But in just some recent measurements that have been able to measure the mass of the rings, it appears to be only two or three times more massive. And we've done that by looking at some spiral patterns in the ring. And an example is shown for the A ring, particularly the wave on the right. That's a spiral density wave by some clever addition of occultation measurements and lining up the phases of the waves, able to look at several waves in the B ring and measure its surface mass density depending on how the waves dampened both amplitude and spacing tells you about how much material you have in the rings. So that gave us an estimate that's only two or three times more massive than the A ring. And now this mass is important because it has implications for the age of the rings. If the rings are more massive then they could be older perhaps forming when Saturn formed less massive then the rings must be much younger perhaps forming from a moon that got too close to the planet or perhaps a series of moons or perhaps a comet was broken apart. The nice thing is in our end of mission orbits we call the grand finale orbits we will directly measure the mass of the rings. We have now the mass of Saturn plus the rings. When we dive in between the rings and the planet we'll have the mass of Saturn alone. And we can take that out and get the mass of the rings. And that the histogram shown there show the range of what the masses might be. And you can see for the B ring the newest measurements are the gold colors that don't go up nearly as far as the brighter yellow bars. And all of these histograms are shown in fractions of the mass of the milimus. Right now we think if you could scoop up all the particles in the rings and put them together into a moon would be about the mass of the moon minus. Another one of my favorite pictures here is Saturn's rings at equinox. Equinox is the time when the sun is edge onto the rings. And in this time period you've basically turned the sun off as far as the rings are concerned. And they're illuminated only by the light coming from Saturn. If you look here in this image what we've had to do is enhance the brightness of the leftmost or lit rings by about a factor of 20 or you wouldn't be able to see them. And over on the right hand side there's brightened by about a factor of 60. And so illuminated primarily by Saturn shine and that bright ring that you see is the effering. The effering is slightly tilted and so it can still catch rays of the sun when the sun is edge onto the main rings. Now it's so exciting about this time is that's a chance to look and see if the ring disc might be warped. If there anything that sticks up above or below the rings the rings on average are only about 10 meters thick. So if you have an object that's larger when the sun is edge on that object will cast a shadow. And so what I show here is an example this is the anky gap with Daphnis. Daphnis is a couple of kilometers in size and it casts a nice long shadow. This also told us for the first time that Daphnis is not orbiting in the same plane as the rings that it's tipped or inclined slightly and this inclination actually pulls particles in either direction from the edges of the anky gap. And some of these edge waves are about four kilometers above the ring plane. We can see their shadows and so on. Another interesting discovery showing this vertical relief in the rings. This is a fantastic picture. This is a view of the outer edge of the B ring. The B ring outer edge is held in place by a two to one resonance with mimus. And it looks like some of the largest particles in the rings have crammed up against the edge of the B ring. And we can see many hundreds of them. Each of them casting their own individual shadows. And a good example of this effect is if you were trying to see the great pyramids out of the space station, if you looked around noon, you'd notice that you, it'd be hard to see them, their shadows are very short. But if you look at dawn or dusk, which is the equivalent of equinox, then the shadows would be long and it'd be easy to pick them out. In the same way, we use this idea at Saturn's rings and looking at equinox allows us to see the shadows of the biggest things in the rings. Here's another example. They're these objects called propellers. They look like tiny dashes in the rings. Here's a view at equinox of one of these objects that you can see it casts a shadow. What we think is some of the largest ring particles are not quite big enough to open a gap like daftness or pan, but instead they create two armed propellers like an airplane propeller. They're trying to open a gap but it's only a very small piece of a gap. And so we aren't actually seeing the object itself but the propeller that it creates to open up this gap. And so some very intriguing, and this is another Cassini discovery. These propellers are kind of fun. They're named after airplane pilots. So there's Blurio and Earhart and all kinds of interesting propellers with their nicknames. Sometimes meteors impact the rings. And this is a view showing with the arrows an angled streak that shows the ejecta cloud from an impact on the rings. And of course equinox is a really good time to look for these because the rings are dark. As you can imagine when there's an impact on the rings it creates a cloud of debris. The cloud of debris comes up above the rings themselves and can catch the sunlight. And this little animation you can see it starts out as a circular cloud and then the differing rotation velocity shear it out into this long linear feature. And this one impact that I've shown here in the A-ring is very similar in size to the Chelyabinsk meteor that impacted over Russia. So we actually see these impacts in the rings as well. Another thing that really stood out in the equinox timeframe is that over a thousand miles of ring, the D-ring and the C-ring had ripples in them as seen by the Cassini cameras. And these ripples, we realized was a tightly wrapped spiral in the rings. And if you can unwrap this spiral you can go back in time and find out when this impact might have occurred. What we think happens is that dust or debris preferentially hits one side of the rings perhaps over hours or even days that tilts the ring. And over time that tilted ring wraps up into a tighter and tighter spiral. And by unwrapping that spiral we can find out when the impact happened. Now we use the same kind of physics that we found here at Saturn. And it turns out that when New Horizons the mission on its way to Pluto flew by Jupiter, New Horizons noticed that there was a ripple also in the Jovian ring. And then unwrapping that spiral, it turns out that that went back to the timeframe of Shoemaker-Levy-9. So that's saying that some of the material from Shoemaker-Levy-9, some of the dust must have impacted one side of the Jovian ring creating a ripple that we see in the rings. This is a view of the F-ring. The F-ring is a narrow ring just outside Saturn's main A-ring. It has tremendous amount of structure. There are two tiny moons, one on either side of it that shepherd the ring basically causing a lot of intricate structure and the ring changes. Every time you look at the F-ring you'll see something a little bit different. In 2007 it actually had this arm of material coming off in the upper panel toward the bottom. Just blowing up a section of that two years later you see all of these almost looks like the spines on a fin of a fish or something. These are all effects caused by the moons that are present around the F-ring. Very dynamic, very interesting ring. As we pull our orbits in closer and closer we'll get a better and better look. And we know that there are parent bodies in the F-ring, large bodies, sometimes they cross through create some of these streamers and structure in the F-ring. Also recently we found that in going back and analyzing the Equinox data in the far infrared that there are regions in Saturn's rings that look unexpectedly young. The ring particles here are much fluffier than they are elsewhere. They're much denser than the fluffy ring particles elsewhere. And so this section of the denser ring particles doesn't heat up and cool down as fast. And telling us that perhaps there was a larger moon or some kind of a larger particle that maybe broke apart could be as much as only 100 million years ago that short in geologic time scale. And its solid fragments are now slowly spreading through the rings and this is what we measured. And it's in the same zone where we see propellers. So maybe the propeller objects are actually remnants of some kind of a collision that happened as this tiny moon broke apart. And what that's telling us is that perhaps Saturn's rings are a mix of old and new. Perhaps regions of the rings are much newer and younger than other places in the rings. We know for instance that the B-ring is so bright because we think that some of the larger particles are like fluffy snowballs. They break apart providing fresh material to keep the B-ring looking youthful and bright. This is a very interesting view. This is from after Saturn orbit insertion showing how much a moonlet can perturb a ring. What I've just showing here are three views that basically the anky gap with pan in it and pan is creating that wonderful ripple in the left most image on the left hand side. You can see daftness creating those edge waves in the rings. And then Prometheus, one of the F-ring shepherds is actually caught tugging material, tugging ring particles out of the F-ring. So there's this tremendous interaction between the moons and the rings. There's a tremendous amount of structure in Saturn's rings. Some of it is driven by the moons, but much of it we don't know what causes that myriad amount of detailed radial structure in the rings. Oh, this is another favorite finding. This is back in 2013. We first saw an object. It was about 10,000 kilometers long on the edge of the A-ring. We knew that there was an object just at the edge of the A-ring, much smaller than that, maybe only a kilometer or two in size. And that we were seeing evidence of a tiny moonlet and Carl Murray, the discoverer, discovered it on his mother-in-law's birthday and her name was Peggy. So he nicknamed this small, tiny moon after her. We've been tracking Peggy ever since. We wonder if she might break free and become a moonlet in her own right or she'll get absorbed back into the rings. And so we'll keep watching her through the end of the Cassini mission. You can also see the bright F-ring and you can see one of the moons Prometheus at the edge of the F-ring. Now, this is a mooniapetus. It's much further away from the rings and yet it also is affected by a ring. Iapetus shown here the leading or dark side and trailing side is the bright side. It has one side as dark as charcoal, the other as bright as ice, all on the same world. And after the Voyager flybys, we wondered is this material coming from inside Iapetus or is it extrinsic coming from outside? It turns out we've now know that there's another ring in the Saturn system. It's called the Phoebe ring. It was actually discovered by ground-based observers and that dust, the Phoebe is a captured moon. It has a highly inclined orbit at 160 degrees almost orbiting retro, essentially orbiting retrograde and the dust from this moon from meteoroid impacts actually then spreads into the Saturn system and is what is coding one face, the leading face of Iapetus. So there's actually a tie between this moon that's much more distant in the Saturn system. Just wanna say a little bit about Saturn. This is a view of Saturn. It turns out that Cassini was in the right place at the right time. There's a giant storm. This storm basically completely wrapped itself around the northern hemisphere and the storm ended when the head of the storm, large hordacy whirling around, collided with the tail which also had a hordacy. When the two of them collided, the storm died away but it lasted for about nine months. These storms occur only about every 30 years on Saturn and only been 20 years since this last storm. You look at different wavelengths. Here this is looking in the near infrared. You can start to see that with the colors, the white is the highest, then the yellows and greens are a little bit lower and then the reds are even deeper in the atmosphere yet. And as you're looking in the troposphere, Saturn is a giant gas ball. It has no solid surface. It's made mostly of hydrogen with some helium and other minor constituents. Looking in the stratosphere, even higher up than the atmosphere than the storm, if you look in the foreign thread, you see a very hot spot looking like almost like a glowing cyclops eye. And this region where the two hordacies collided somehow transported tremendous energy into the stratosphere and we've been watching it slowly cool. Of course, another very interesting thing, this is the hexagon at Saturn's North Pole. It's a six-sided jet stream. It's about two earth diameters across and in the very center is a hurricane. You can see that reddish hurricane. This is all in false color and pink here in this view are the clouds. In the 1980s, voyagers saw this hexagon, this six-sided feature, and it's still there to this day. So it's very long life, whatever it is. And here's a close-up view of the hurricane. It's about 50 times larger than a typical hurricane on earth. In this false color view, we've nicknamed it the rose. It's a very pretty red color. You can actually see the shadows of the eye wall from this hurricane. Wind speeds are about four times the typical wind speeds of the hurricanes on earth. And the ring shadow is marking the passage of the seasons. What you see here is the shadow of the rings. When we've at Equinox, that shadow went all the way out across the rings. And now it's pulling in. It's just a little bit past the orbit of the Cassini division. And by Equinox, the solstice in May, that ring shadow will be pulled into about the center of the B ring. I want to say a little bit about Cassini's grand finale. That grand finale are those final 22 orbits where Cassini will plunge in between the gap and the rings and the Cassini team. Basically now we've been together so long we see ourselves as a Cassini family. We'll be gathered as Cassini collects data and learns new information about this interesting world. And for many of us, Cassini is also a member of the team that she's really a part of the family. And we've just been so amazed by so many of the discoveries that she's made along the way. And look forward over the next year to additional discoveries and new views, especially close views of the ice humans that she'll see in the future. This is the solstice mission trajectory and all of the orbits of the last seven years shaped by Titan. And here are the tiny orbits I'll be talking about at the end, the F ring and proximal or grand finale orbits. They're only about seven days long, each of them. And so time will go very quickly as we get into this series of orbits. Key orbital characteristics, there's 42 of them. They begin the end of November this year through to September of next year. 20 F ring orbits where we bring the periapse in the closest point of the orbit, closer than we've been before, just outside the F ring. And that's gonna set us up for that final jump into these orbits. And as you can imagine, I'm excited as a ring scientist to get these really high resolution views of the F ring and of the A ring. And also some very interesting occultations as well. And this is the view from the earth of the Cassini orbits. We basically have the periapse close to noon. This helps us with our gravity measurements. And then the grand finale orbits, 22 final orbits for orbiting in a narrow, clear region between the innermost ring and the top of the planet and the first orbit, the first passage through this area is on April 26th. Now we're not in a polar orbit, instead we're at what we call a critical inclination. This inclination, given the ablateness of Saturn, keeps the orbit from precessing and running into the ring. And if we have any Delta V, then we're gonna go. You may now return. If we have any Delta V, if there's any Delta V available, we're going to go lower. It turns out that Saturn's atmosphere is shrinking. We have a model for that. If it shrinks more quickly, we'll use some of our remaining fuel to actually lower some of those final orbits on Cassini. Our current impact date is September 15th, 2017. And they were basically performing a mission very similar to Juno, only in this case with Cassini-like instruments. Here's a movie. If you could write along with Cassini, what minds you see? This is actually plunging through the gap. This whole movie actually happens over a little over an hour time span for Cassini. You can imagine yourself holding tight to Cassini and actually diving with her through that ring gap over and over again for 22 orbits. And I call this seven seconds of terror every seven days for 22 orbits. Some unique end of mission science. We're gonna get both gravity and magnetic field measurements. You can think of those as a window to the interior of Saturn and determine the gravity and magnetic field to very high order and actually get a measurement of Saturn's internal rotation rate for the first time. And that will be very exciting. And we're also going to get the measurement of the ring mass, as I said, right now it's uncertain to about 100%. We're hoping to get that down to about 5%. We have six gravity arcs devoted to these studies. We're gonna measure the ionosphere, the in situ plasma, the radiation belts for the first time and the aurora and the magnetosphere. So it'll be very exciting for the bills and particles instruments. Highest resolution of observations of the rings we're actually gonna actually use the radar to make measurements of the rings because we're in so close. The highest resolution studies of the atmosphere and of the poles and of the aurora of the planet. And this is just the summary of the points that I covered and just want to highlight that while Cassini is performing its grand finale set of orbits at Saturn, Juno will be doing the similar thing at Jupiter and so we'll have a chance to compare the results about interiors and tell us something about the planetary evolution on two of these missions that'll be taking data at the same time. So we'll be collecting science that's very complimentary to the Juno science on collected there. Just want to talk a little bit in closing about the timeline for the grand finale. On November 30th, that's when the F ring orbits begin. This is with a fixed longitude frame showing you what the longitudinal coverage will be for the magnetic field measurements. There are 20 orbits and only three maneuvers to keep us on course. On April 22nd, we get a nudge from Titan. This trajectory shows just how powerful Titan is. Each Titan flyby is equivalent to the amount of fuel that Cassini burned on Saturn orbit insertion. And since Titan is such a large moon, it really provides a tremendous amount of bending to the Cassini orbit. So as the orbit closes, you can see in that small box, we get a close flyby of Titan. And that close flyby of Titan really bends the orbit of Cassini. And it's this bending from that, our final close flyby of Titan that actually allows Cassini to shoot through the gap and start its set of grand finale orbit. Then in April, we begin the grand finale 22 and a half orbits. Nine distant flybys we call non-targeted flybys of Titan. And on April 26th, that's our first dive through the gap. Again, this is similar to show that the coverage and longitude for each of those 22 orbits now threading through that gap between the rings and planets. And on September 11th, we have our last non-targeted flyby of Titan. Titan's gravity even from hundreds of thousands of kilometers away. It's great enough to put Cassini on a trajectory, push us into the atmosphere of Titan. And on September 15th, that's the day of Saturn impact and would mark the end of the Cassini mission. And on that day, I just have a view here of some of the many people that work on Cassini, the scientists, engineers, all of the support staff that make Cassini such a great mission. I'm sure we'll all be gathered on that final day. We'll be pointing the high gain antenna at the Earth to send back data as long as we can because our ion and neutron spectrometer will be measuring the atmosphere of the planet itself. We'll be gathered on that day watching the DSN signal until finally that signal stops. At that point, we'll know that Cassini is in Saturn's embrace and the atmosphere is so dense it will turn Cassini away from the Earth. And then over a very short time, the Cassini spacecraft will probably be torn apart and bits of it will melt. And you can think of it as the atoms of Cassini, all the bits of her that made up Cassini will become one with Saturn. And I know that then when you go out and look at Saturn in the future, you'll say, ah, I know a little bit of Cassini is there as well. Now, after the Cassini mission ends, the observations of Saturn will be up to you, the ground-based observers. And with that, I'd like to end my talk and take questions. Thank you very much. Okay. Well, thank you so much, Dr. Spilker. And so I don't know if you want to put your video back, you know, stop sharing your PowerPoint so that we can see you. Okay, sure. But we do have a few questions here. And so going back towards earlier in the program, we had a question regarding Enceladus. Does it have an active magnetosphere and tectonic plates? No, Enceladus does not have an active magnetosphere. We've looked for evidence of a magnetic field, and it doesn't have one. It doesn't have tectonic plates in the same way as the Earth. It just has places where the crust has been fractured, perhaps by movement in the ice, but not plates per se. Most of the activity we can see tectonically is at the South Pole, although there's an intriguing fracture at the North Pole as well. Okay. Another one staying with Enceladus. So Ted asks, if living organisms exist in Enceladus's ocean today, is there any reason to believe they would not be ejected out into space along with the inorganic particles in the jets? Right. That's great. That's why on the slide I showed, Enceladus is providing us free samples. And Cassini, unfortunately, since we didn't know ahead of time about these icy plumes at Enceladus, we didn't carry instruments that could directly look for long-chain hydrocarbons, amino acids, fatty acids, evidence of life. And I think that would be a great reason to go back with a more sophisticated mission, carrying the instruments that could actually make the measurements to answer the question, is Enceladus a habitable world? Is that ocean truly habitable? And might there be signs of life? It might be life as we know it here on the earth. It might be something that took a different branch along the way, or it might be something very, very different from anything that we've seen before. So we'd have to be ready for all of those. Okay. We have another question here coming back to the proximal orbits. Will the occultations during the proximal orbits be of radio emissions from Cassini passing through the rings and being received on earth? Or is Cassini actually looking at stars on the other side of the rings and measuring the occultation of starlight? That's a good question. We have multiple kinds of occultations. If we use the radio signal itself to the earth, that radio signal will then pass through the rings or the atmosphere of the planet. That's one type of occultation. Another one is we could use a star or the sun and use instruments on board Cassini to measure if the star or the sun goes behind the rings or the planet itself will learn about the rings or the atmosphere. So we have actually three kinds of occultations we can do. Okay. So let's see. We have another one here. This might be one for the night sky network team here asking if the night sky network team is going to be working with the Cassini group for a possible outreach opportunity for us to engage the public at the end of the Cassini mission. That's a good question. That's a good question. I think it'd be interesting to be looking at Saturn at the time. Cassini goes into the atmosphere. It'll be on the day side. It'll be visible from the earth, but since it's on the day side and Saturn is so bright and Cassini is so small, it's not clear. It's very unlikely actually that we'll see anything like a Shoemaker-Levy 9 kind of an impact. Okay. So let's see. David, do you have anything else on your end? Well, I actually, yeah, we have actually a question that popped up in chat from Carol Bot. She was asking, she has several questions here. Okay. What was the black region in the infrared image? I think that was from that big eye from the storm earlier. There's another question. Why did the edge of the B ring look ragged like icicles and aren't all the rings made of small, round particles? Yeah, I'm not sure about the black region. I guess Saturn, there was the bright feature that looked like an eye. And then it was dark around it because it was much colder. So that was a temperature map of Saturn. The edge of the B ring looked jagged because of those shadows coming out from the largest particles sticking out. In general, the ring particles tend to be small. They tend to be millimeter size, centimeter size, up to maybe tens of meters for the larger particles, propeller objects, et cetera. But at this case, the edge of the B ring in this particular region had particles that were maybe half kilometer to a kilometer in size and lots of them plastered right at the edge of the B ring. Edges are generally fairly smooth, except for when they might undulate due to wakes or waves created by interactions with the moons. And I had another question. Actually, I have one. This is for me. I heard about different end of mission scenarios. And one of the ones that was like stood right out, but seemed like it was pretty difficult to do was one of the ones mentioned supposedly was some orbital wizardry to schlep it over to Uranus or a Centaur or another object. How, how likely was that? Like how much consideration was given to that versus just straight up continuing the mission at Saturn? Yeah, it was given some consideration early enough in the mission where we still had the fuel left. We could have done that, but it would have been a very, very long trip to get all the way out to Uranus or, or especially to an object even further away. So we looked at would we have enough power because we have these radio isotope through electric power generators that slowly plutonium is decaying a little bit every year. So our power is going down bit by bit. And then it would just be the age of the spacecraft by the time you got all the way out to Uranus. So we did look at that. We knew we had to do something with Cassini, crash it into a moon and the mission in some way, because we have two worlds actually that have liquid water oceans. And then we have the solidus and also Titan as a liquid water ocean underneath its icy crust. And so to protect these two worlds, these two ocean worlds, NASA would then require us to find a way to make sure that Cassini, once the fuel was gone, wouldn't accidentally crash into one of these worlds. And so, you know, the unique science we could get going in close to the planet was by far and away the favorite with the scientists and also allowed us then to make sure Cassini by going into Saturn wouldn't accidentally impact and solidus or Titan. And it looks like we have one last question here. This has more to do with the engineering of the spacecraft. Dwayne asks, who built the sensors? Oh, the sensors on the spacecraft. If you're talking about the instruments, the instruments themselves were built by teams that literally are spread around the world. The Cosmic Dust Analyzer came from Germany, the magnetometer from the UK. A number of instruments came from different universities right here in the United States. Some from the Jet Propulsion Laboratory as well. And if you get to the sensors on the spacecraft, the ones that take the op-naves or measure the power in the voltages for Cassini, a lot of those were built by contractors and then put together here at JPL. In fact, I remember watching bit by bit as the Cassini spacecraft was built and put together here at JPL. Okay, we had a couple of last questions coming real quickly here. Michael asks, and then there's a related question from Dave. Michael asks, will the radioactive plutonium in the reactor contaminate the atmosphere of Saturn? And then Dave kind of extends that and say, will the spacecraft be totally destroyed on impact and consumed? Well, as Cassini is torn apart, yes, all those bits of plutonium will become part of Saturn. Saturn though is just mostly gas, so we're not worried about contaminating any life, mostly hydrogen and helium. And what we think will probably happen is Cassini, it won't, since it's an atmosphere, it'll go into Saturn's atmosphere and it'll be so hot that the heat from the atmosphere will ultimately sort of melt and just get Cassini down to the atoms from which she was constructed. Imagine like a giant meteor coming into the Earth's atmosphere just not making it to the ground. So grounded Saturn, and so those bits that are Cassini will just be spread throughout the atmosphere. Okay. A great fireball if you could be there and watch. Oh yeah, that would be a great fireball across the atmosphere. And this will be the last question. I'm going to reinterpret Jim's question and say, are there any really interesting features that you noticed out there that you just playing and didn't get a chance to investigate? That's a good question. One of the things I didn't have time to mention involves a moon, Tethys. And Tethys has these red streaks on its surface that looks like someone took a piece of chalk or lipstick and just up and down the craters and whatever drew these red streaks. And we've imaged them up. There are no fractures associated with the red streaks. And we've just recently discovered them and we haven't had enough time to really follow up. So that's one of the puzzles that we'll leave for a future mission. Okay. And with that, I want to say thank you very much for joining us. This is really wonderful. You'll be able to find all of the Night Sky Network folks. You'll be able to find this webinar along with many others on the Night Sky Network under the Outreach Resources section on the NSN website. Just search for webinar. We will also be posting tonight's presentation on the Night Sky Network YouTube page by the end of the week, where you can also find other resources and activities on the dedicated research page. So please mark your calendars for our next webinar on Wednesday, October 26th, when we welcome Dr. Pamela Gay, who will share with us how all of us can get involved with analyzing NASA data through the many citizen science portals under the CosmoQuest umbrella. And there might even be a Saturn one forthcoming in the next few years, we can hope. And so there's a lot of data that you have to be looked at. So keep looking up and we'll see you next month. So good night, everyone. Good night. Good night.