The Sackler Lecture in Astronomy: A Decade at Saturn

welcome to the 2014-15 Raymond and Beverly secular Distinguished Lecture I am my name is MK dupatta I'm the chair of the Astronomy Department and the first thing I'd like to ask you is to please turn off your cellphone's I would like to thank Raymond and Beverly Sackler for their generous donation which established the fund to support his annual distinguished lectureship in astronomy and be very appreciative of their vision which allows astronomy to host these annual events with illustrious speakers such as Carolyn Porco whom you will hear today dr. and mrs. Sackler our highly respected international philanthropist in the sciences and the arts with a long-standing commitment to support scientific research and exchange they have a longtime association with UC Berkeley although the sector's are not here today we will be sending them a DVD of this event so our speaker Carolyn Porco an adjunct professor at the University of Colorado leads the Cassini imaging team she's also an imaging scientists on the New Horizons mission to Pluto which will fly by Pluto this July her specialty is the study of planetary rings and the ring moon interactions and the study of geysers on Enceladus one of Saturn's many intriguing moons a frequent public speaker carolyn has appeared on milt multiple times on CNN and CBS and she gave also to TED Talks she has consulted on award-winning films such as the 1997 film contact based on novel by the late Carl Sagan in 2008 she was invited to join the production crew of Star Trek as a consultant on planetary imagery she participated early on and laid a plan to take images of Earth's from afar such as through Saturn's rings there are planets Europe as the famous P Blue Dot Carolyn has been a recipient of a number of awards and honors for her contributions to science and the public for example she has an asteroid named after her asteroids for coal in 2010 she was awarded the Carl Sagan magnet medal presented by the American astronomer Astronomical Society for excellence in the communication of science to the public and in 2012 she was named one of the 25 most influential people in space by Time magazine and without further ado I like to invite Carolyn to start her lecture a decade at Saturn Thank You India and thank you to the astronomy department for inviting me to give this very prestigious lecture and I'm coming to you from Boulder Colorado and I want to commend you on your choice of weather I mean really you guys know how to do it so anyway I'm going to begin this lecture with the story and it's a remarkable story about the inhabitants of a small rocky ocean covered little world in orbit around an ordinary star one of hundreds of billions of stars in an ordinary galaxy and as this story goes these beings refusing to accept limitations and laughing at the idea of boundaries over time developed the languages of mathematics and science they became skilled technologists they developed mastery over gravity and eventually flung themselves in their machines into what they called outer space and they did this merely in response to an innate desire to explore and to learn about their cosmic neighborhood but they did it also because of a desire to secure the future of their progeny and to seek the answers to questions that had vex them and every generation of their ancestors before them how is it that their small planet when they living on it came to be and what was the great cosmic theater in which life on their planet had unfolded well you probably figured it out already this is a story about us and we humans have been interplanetary travelers now for over 50 years and in that time we have been to every corner of the solar system we have sent our robotic spacecraft to all the planets all eight of them we have landed on asteroids we have just recently landed on a comet we have a spacecraft knocking on the door of the Kuiper belt to visit its most famous member ludo and what and in what I regard is humanity's finest hour we even set foot on our own moon and when you think about it this is an outrageous story not only about scientific discovery but about extreme exploration and the thrill of adventure and a major chapter in this story began 24 years ago when a mission to Saturn called Cassini was finally begun and it was a joint effort between the United States and Europe and from its conception it called for a comprehensive in-depth examination of everything in the Saturn planetary system the planet its magnetosphere its enormous collection of rings and its collection of many many moons and last summer we completed our 10th year of being in orbit around Saturn and obviously there's no way I can compress ten years of findings into just one hour so I am going to take you this afternoon on a tour of the highlights just give you the highlights and especially those that can be best conveyed with images because after all I am biased and then I will conclude with what I consider to be the greatest legacy that the Cassini mission will leave behind once it's over now Saturn is very far away and Cassini at launch was very heavy it was six metric tons and the size of a school bus and even launching Cassini on the largest rocket that we had in the American arsenal at the time that was a Titan four missile and even strapping on solid rock rock solid rockets to that and putting a centaur upper stage on that and putting Cassini on top of that whole stack was not enough to get it directly to Saturn and so what we did was we looped it around the inner solar system twice visiting Venus twice that two years visiting Venus twice and the earth once all to gain speed from what are called gravity assist maneuvers and then in a terribly poetic on the eve of the year 2001 Cassini flew by Jupiter for a final push to Saturn when it arrived three years later now you can appreciate the object of the exercise is to get the spacecraft to its target as quickly as possible so that those of us who were involved in the mission is still alive by the time the spacecraft gets there and so that means that by the time it got there it was absolutely screaming by and we had to slow it down and that's shown in an artist's depiction here what we call the Saturn orbit insertion maneuver when we burned more than half the mass of the spacecraft at launch which was fuel we burned it in order to we didn't actually slow down the speed we slowed down the acceleration so that it could basically drop into orbit around Saturn which we did on July 1st 2004 and once in orbit Cassini began its tour of the Saturn system and that was characterized has been characterized by many orbits they change their orientation their size their inclination and so on and that's because doing this allows us excuse me to see all the targets in the Saturn system we want to be in the equator plane to visit the moons that are there and to get good views of the equatorial and mid latitude regions of the planet and so in the moons and then we want to crank up the inclination so that we can look down on the polar regions of all those bodies and also see the Rings as well and herein lies the heart of our success and orbit a mission as you can imagine is very much different than just a flyby we have the luxury of finding something and then maybe weeks months even years later going back for another look so that we can really come to understand what it is that we're finding and we've done this in many many cases with Cassini one of the main objectives of the Cassini mission has been to study the planet itself in particular it's meteorology and in the past 10 years we've learned a tremendous amount about the atmosphere of Saturn the life cycle of storms speeds of the winds and the role of Eddie's and so on but it just so happened we were there to see like the granddaddy of all meteorological meteorological phenomena and that was the eruption of this major huge colossal storm in the northern hemisphere of Saturn the kind of storm that happens only once every two or three decades we were there to visit it this storm was the largest had ever been seen obviously from a nearby spacecraft and it lasted some 2/3 of a year it was thundering and convecting with lightning strikes ten times the rate of any other smaller storms that we had seen on Saturn and it appears we're not sure yet but what appears that these kinds of storms erupted like volcanoes they've pressure bills and bills until finally they erupt and it takes 20 years for that to happen obviously very much different than the kind of weather and meteorology we have on the earth there is as much power in this storm as is coming out of the whole planet so these storms may play a big role in the the energy balance within the planet and all that is still under in under examination then as spring marched on in the northern hemisphere we got really good views and saw in great detail a feature that had actually been discovered by the Voyager spacecraft two plus decades earlier and that is the hexagon mm this is a feature that is about to Earth's wide across the winds blow in it at 220 miles per hour and I swear whenever we put anything about the hexagon out there's public release on our website the hits go through the roof because people think they must think this has something to do with crystal energy or something but I assure you this is no more mysterious than a regular garden-variety jet stream just like we have in our atmosphere it's just a jet stream with six waves in it and like our earth this is video that was I just pulled off the Goddard Space Flight Center website it's real data showing our jet stream our jet stream is obviously much more discontinuous and irregular and the reason for that is the atmospheric systems on the earth when they blow they move over Hill and Dale and Ocean there's a lot of friction in them they run the systems down they have to get started all over again on Saturn that doesn't happen there is no friction so things are much more stable all meteorological systems on the giant planets are far more stable than they are in our atmosphere the the Jupiter's red spot has been ongoing for hundreds of years okay all because we think all because there's no friction but anyway there's nothing peculiar about the hexagon in fact I've I've encouraged people not to even call it the hexagon anymore and you can tell all your friends that - there's nothing to get weird about anyway we use false-color a lot to distinguish different heights in the atmosphere and this is false-color used to look at where the features in the north are lying like these clouds here are very high this here is very low and this is a vortex exactly at the South Pole and one of the most beautiful images that we and my group have produced we're responsible for producing and you know releasing to the public all the pictures that come from Cassini and this one made it to Brian Williams on the nightly news because he loved it so much - and this is what that vortex looks like it's basically Saturn's equivalent of a hurricane it has an eye wall it has winds in it that blow 330 miles per hour that's 50% higher than the winds that leveled Moore Oklahoma a few years back and it is about a half the u.s. across so it's a major another major meteorological thing in Saturn's atmosphere that we're spending a lot of time looking at the Rings of course are what makes Saturn the icon what is that I don't know anyway just hope that doesn't come up again mmm the Rings are what makes Saturn the icon among planets that it is they are a tremendous visual spectacle 280,000 kilometers across that's about one light second and they would fit roughly from one end to the other roughly in between the Earth and the moon they consist of countless icy bodies made largely of water ice and they range in size from the finest talcum powder to particles or bodies as big as large houses and they speed around Saturn at enormous speeds of 20 to 40,000 miles per hour but they only very gently nudge each other at millimeters per second this is what physicists call an equilibrate Assist 'm so any violent collisions in this system died a long time ago and because of that they are paper-thin relatively speaking they're only one or two stories in a modern-day building thick despite the fact that they are one light-second across and bear in mind that they are also tracing out the plane of gravitational equilibrium around the planet so they are very very mathematically precise despite their physical size if you took all the mass and Saturn's rings and recomposed it pushed it all together to make a moon of the proper density for the Saturn system it would be no bigger than this little moon here so lots of drama and visual spectacle for actually comparatively little mess and these shadows here are actually the shadows cast by the ring system onto the northern winter hemisphere of Saturn now the Rings exhibit an enormous variety of structures we've got good a good idea of just what kinds of structures were there from the Voyager mission in the early 1980s and now with Cassini after 10 years we've come a very long way to knowing exactly what causes all this structure astronomers have known imaginations what so ever so I've apologized for the names of these features they the B and the C ring they actually are all very different in structure to one another and the B ring is where most of the masses that's the ring that casts the darkest shadows we were really perplexed about what caused all these features and Voyager days we have pretty good understanding of it now at least we think we do this is the most diaphanous ring of the main rings you can easily see through it it's characterized by these plateaus of higher than average concentrations of particles but otherwise it's very very thin and the a ring is the ring that every feature you see in it is due to a gravitational resonance with an orbiting moon so we know a lot about the a ring and I'm going to say much more about what goes on at this outer edge here the orbit insertion maneuver that you saw saw an artist depiction of brought as closer to the Rings than we had ever been during Wellman's that we've been since the mission started and we flew over the dark side of the Rings and we convinced the engineers at the Jet Propulsion Laboratory who really did not want us to do this to take the spacecraft during this event actually after the burn was over take the platform on which the remote sensing instruments is situated and point the instruments down so we could take images as we flew along the Rings knowing that this was going to be the most detailed view we would have of the Rings and we finally won that argument there's a lot of arm wrestling and what we saw a lot of were waves okay these are the waves that I just told you they're due to the gravitational interactions with orbiting moons here is a density wave what happens here oh by the way the tiniest blip here is about two and a half football fields across so here is a density wave what is going on here is the orbiting moon is making the orbits of the particles eccentric not circular and those eccentric orbits are all phased relative to one another to give rise to these lanes of higher than average concentrations of particles that spiral all the way around the planet these are the kissing cousins of the spiral arms in spiral galaxies in fact the mathematics and the physics that was used to explain the spiral structure in disc galaxies was co-opted and with very little change was applied to the study of Saturn's rings to prove that when voyager got there we would in fact find these features and that's exactly what we found that was my thesis adviser who predicted that and and this is the vertical equivalent of a spiral density wave it's a what we call a bending wave here it's not the eccentricities of the particles that are being excited it's the inclinations so the particles are because of a moon that's on an inclined orbit the particles are also excited into inclined orbits and they are also relatively phased so that they give rise to well imagine corrugated cardboard that's what the ring is doing in these regions the whole ring plane is warped to the tune of something like a kilometer or kilometer and a half so anyway we can read these features like books we read the wavelength we read the the decrease in the wavelength with distance and the amplitude of the waves to tell us things like how densely the the material is packed how vigorously they collide how easily or not they're losing energy and so on so it's really been a tremendous boon to have this series of images that we took during the Saturn orbit insertion and these looking at these features that are created by ex moons that are external to the Rings some of the most dramatic features that we have seen in the Rings in fact are created by moons embedded within the Rings here is a close-up of the inky gap it's near the outer edge of the a ring that I pointed out before this is a moon pan that we imaged later on in the mission this was taken during the Saturn orbit insertion maneuver when we ended up moving on to the lit side pen is responsible for creating all this structure so it this was glorious and then when we looked at the Keeler gap which is right next door to the outer edge of the a ring we found this moon deafness and it is about eight kilometers across and it is responsible also for wiggling the edges of its gap where it lives and one big surprise for us is that deafness is on and inclined orbit it's not something we expected and I'll say more about that in a minute mm-hmm now these kinds of observations would have been a tremendous bounty for any ring scientist because as I think you're probably catching on now they speak volumes about the interactions that moons have with rings and what they tell us about the ring disk of material the nature of the ring particles how much energy they lose in collisions and so on but one event we knew was going to give us the best chance we'd get to see the Rings in three dimensions was the exact moment when the Sun traveling from south to north as seen from Saturn was shining directly over Saturn's equator and edged on to the Rings this was the northern vernal equinox and it occurred in the summer of 2009 that's Earth's summer 2009 and that was the moment when spring arrived in the northern hemisphere on Saturn it was absolutely magnificent because it was a spectacle that no one had ever witnessed up close before and that moment is shown here in a mosaic that I deliberately planned just so we could say we saw equinox on Saturn and see the whole system we had to seriously play with the brightness in this picture the right side of the Rings which you can see here clearly we had to brighten them about a factor of 60 in order to see it this is really lights out on the Rings and the reason why this part here is brighter is because it's sunlight shining off Saturn and back onto the Rings but the only thing that illuminates this is the light scattered along the edge of Saturn onto the Rings so it's really dark here anyway for those of us paying attention to this event it was the first time since the discovery of the Rings in four four hundred years ago that it seemed as if by magic they just suddenly popped into the third dimension and here's just for starters some of the things we saw remember deafness in the Keeler gap wiggling the edges of its gap we'll take a look at it now okay it is casting its own shadow because it's inclined and these things in the edges are really mountainous walls of rubble two and a half miles high above a ring that is only thirty feet thick okay we did not really I mean we kind of expected because it was an inclined orbit it might be drawing ring particles out of the ring plane we never expected this to be so dramatic and I love imagining flying low across the Rings in a shuttlecraft okay and to your perspective the Rings would look like they go on into infinity so there's bright gleaming sheet of material all around you and you're flying along and you come upon a wall of rubble two and a half miles high that needs to go in a movie and there's vertical structures everywhere here's the outer edge of the earring this is the F ring I'm not going to say anything about all these things here that look like little bumps they're actually density waves we were very surprised to see that they had so much three dimensionality to them obviously the particles are being squished so far together in these waves and since the particles aren't compressible they just all kind of you know go pile up on each other and they create things that can cast shadows this here that here this year those of bending waves that's where I said that the ring plane itself is warped and I want to point out to you this feature here this is the Enki gap pan is in that that gap but this feature here really caught our attention and when we look up close we notice that it is in fact a feature that is created by an betted moonlit that is about 400 meters across so about a half a kilometer and it is agitating the ring material around it to create these propeller features that's what we call them because they're kind of canted to the direction of motion and they we've seen dozens of these in our images and from that we can infer the presence of millions of them there are lots of small moon lights in Saturn's rings that are way bigger than the largest particle of any number inside of any number and that was like I said the size of small houses this is quite bigger than a small house and there's millions of them so this was just a great window onto what the character of the Rings system is like and you know we are interested in studying rings because they give us they tell us about processes that went on that are going on now in disk systems that we're discovering around our galaxy around stars and also that happened long ago in our solar system before the before the planets formed so or as the planets were forming and we have been able to observe the motions of these bodies the largest ones and we see them drift across the Rings mimicking the migratory motions that we believe the planets underwent as they were forming in the solar nebula so Ksenia has been a great advance in our knowledge of ring systems and the processes that go on within them within solar systems and even within the spiral disk galaxies that are present throughout the universe so it has this is why I always say Cassini has enormous cosmic reach in the kinds of things that it is it is shown us now speaking of moons Saturn is accompanied by a very large and diverse collection of them the skies of Saturn are literally spangled with moons there's more than 60 of them I've lost track I don't know anymore how many there are but there's a large number of them and they break up into two groups there is the outer group that is from about 10 to 20 million kilometers away from Saturn and beyond those are the irregular Z have very irregular orbits that's why they're called that they're very inclined some a retrograde some are pro-grade you can almost think of them more like a cloud or a very very thick disk of bodies going hither and thither and then there's the inner satellite system that goes from basically Saturn's rings out to about three or four million kilometers and that is the system that we believe formed in an analogous way to the to the solar nebula and to the way that the planets forms so our goals in studying the Saturnian satellites with Cassini were not only to do a survey of this inner group and see if there were any moons that hadn't been discovered yet from the ground and we found a few that were small our goals were not only to come away with accurate measures of the physical characteristics of these bodies like their sizes their shapes their masses their densities and so on and not only to advance our understanding of their geological and thermal histories which we've been busy doing but also to look at them as a system with an eye towards testing and refining our notions about the planetary processes that are involved in the formation of solar systems both our own and others that we're discovering today and we've been doing a lot of this over the last 10 years made possible of course by the orbital tour that I showed you that is truly unprecedented in magnitude in anything that NASA has done you saw Cassini's changing orbits but many of those took us very very close to the moons of Saturn lots of them as close as the space station flies above the earth and at least in one case that I know of 15 miles above the surface of a moon so I mean we've gotten very very brazen in visiting the Saturn system we started out kind of tentative and now we know we can do this and we've had well over a hundred close flybys of moons in in the Saturn system and through it all we've taken some incredibly beautiful pictures that I want to show you just because they're beautiful pictures keep in mind as I go through this our moon is 3,500 kilometers across that's about 60 percent the size of the u.s. so here you've seen this one already it opened my talk this is the winter hemisphere of Saturn soon after we arrived and this is D&E it's a moon about the third 1/3 the size of our moon here is do knee against the disk of Saturn we're pretty much in the equator plane the Rings look very very thin and this is the do nice skyline showing the very pristine white of ramparts icy ramparts of a crater I just love imagining a astronaut go walking accustomed here is thethis tet this is a little bit smaller than dyani so much smaller than our own moon sporting some big basins with the Rings the unenumerated side of the Rings Beyond and this is one of the strangest this is Hyperion it's a quarter of the size of Texas so it's small it's about the size of a state maybe it's the size of Texas or something like that and it's looks like something that was kind of taken out of the ocean we know what caused this I don't have time to tell you though this is me miss seeing against the shadow draped winter hemisphere of Saturn with the Rings in the foreground and this is a closer look at me miss it is our Death Star the tiniest dot here is three kilometers we know that the projectile which created this crater which is called Herschel crater came very close to smashing me mr. bits so it doesn't take a rocket scientist to figure out that there must have been moons around Saturn that did get smashed up to bits and that in fact is one of the main ideas we've had it for a long time I think it's still a reasonably good idea of Saturn's rings got there that a projectile either from within the Saturn system or maybe from out beyond the Kuiper belt came in ventured to close hit a moon and that moon disrupted and the natural course of events after you get a debris cloud like this the first thing that happens is it completely encircles the planet and then eventually over time with collisions that lose energy but conserve angular momentum the ring the material compresses down to form a ring so this is still a reasonably valued idea for how rings form but I've come up with my own idea of how rings come about and I want to share that with you now okay so that's that's that's my idea for how rings come about I'm just having a little bit of a problem getting it published anyway two of Saturn's moons are absolutely standouts I don't think you'd get any argument with this Titan is Saturn's largest moon it's fifty percent larger than our own moon and until Cassini got there was the largest single expanse of unexplored terrain that we had remaining in our solar system and Enceladus as you can see it's an icy body about the a tenth the size of Titan we learned a great deal about Titan from the Voyager flybys in the early 1980s we learned despite the fact that we could never see the surface we learned that the Titan atmosphere was marvelously like the Earth's it was largely molecular nitrogen it has a thermal structure like the Earth's troposphere stratosphere and mesosphere the surface pressure is comparable to what we have here actually 50% greater but it was different in some very important regards it has no free oxygen and it was suffused with small amounts of organic compounds like methane and ethane and propane and benzene and so on and it is these compounds that form a ubiquitous 200 kilometer deep haze that gives Titan its orange color and makes it makes the surface very very dark high noon on Titan that the surface is as dark as deep earth Twilight is on the earth and over time it was believed people calculated you know what would happen and it was believed these haze particles would you know form larger haze particles they they you know they're colliding with one another they fall down to the surface and over God knows how long hundreds of millions of years tens of millions a billion we don't know would eventually cover the surface in a thick organic sludge and some of these compounds methane in particular could be liquid at the surface conditions that we were able to divine from the voyages mission in fact methane's at its triple point it can be liquid it can be ice it can be gaseous despite the unimaginable cold of three hundred degrees below zero Fahrenheit and so this opened up it just literally a world of bizarre possibilities you could have patchy methane clouds you know floating above an icy sludge covered ground in places you could have gentle rains that fall and and cut gullies and form rivers and cataracts and then form deeper canyons and wash the sludge off the high mountain peaks and into basins and craters and low-lying depressions and so on and that's what people believed might be on Titan so just you know stop for yourself and imagine what this environment is like you are standing on a moon in the outer solar system you're standing on Titan you're probably tired of course it's dark it's eerie it's extremely cold it's misty there's a gentle methane rain washing over you and you are standing on the shores of Lake Michigan brimming with paint thinner and that's what we thought was wood we would find under the haze on Titan and so you can imagine we were very eager to find out if we were right and for this reason Cassini was equipped to the gills with instruments to study Titan our investigation of Titan was planned like the you know the the the Normandy invasion of World War two that's how I the analogy that comes to mind for me it was serious stuff and several instruments on the orbiter had the capability to D to see down to the surface my cameras were were two of them you know scientists had learned the trick between Voyager and our arrival at Cassini that you could see down to the surface of Titan if you knew what wavelengths to look at you couldn't see in the visible voyager only had the capability to see in the visible but we learned if you looked at particular spectral regions in the infrared you could actually see down to the surface so we were sure to equip our camera with filters that could look in those regions and then of course Cassini carried a radar instrument just like the radar instrument that was carried by Magellan which mapped the surface of Venus despite an incredibly thick impenetrable to visible light anyway atmosphere that Venus has and so Cassini has a radar too so we were we have been able to understand what is going on on the surface of Titan and to show you what properly equipping your spacecraft can do for you here are our pictures taken with our cameras in the visible and in that spectral region I told you about this in fact is a wavelength that is equal to the wavelength used by your television remote okay and I'll say you can just see here this is pretty much what we saw it was very hard for us to figure out what was going on on Titan the first few months of orbit because remember it's dark it's hazy it's always a hazy day on Titan and there are no shadows so we could not use the technique that we have been employing for 50-plus years to study airless bodies in our solar system which is you see a picture of the surface you know where the Sun is you could see the shadows you could tell what's up what's down how tall and so on we can't do that on Titan we could see in places it looked like there were channels and of course we were expecting channels and we thought we saw some and we thought we saw things like maybe a few very very few craters anyway we were having a very hard time seeing what was going on in Titan and then of course came the Huygens probe which the deployment of which happened six months after we got into orbit and this was a flying saucer shaped device built by the Europeans and carried to Cassini carried by Cassini to Saturn that I mean get your head around this drifted down through the atmosphere on a piece of fabric and finally came to rest after two and a half hours on a moon in the outer solar system I mean I'm always blown away by this it took many measurements on the way down atmospheric opacity composition winds it spun deliberately as it fell and it had cameras on it so panoramic pictures were being taken all the time and it was very it's very difficult to describe what it felt like to see the first images from the surface of Titan from the Huygens probe they were everything our pictures from orbit were not and here they are in mosaic form and you could clearly see that it's colorized there was no color that to speak of this is a dendritic drainage pattern I mean it was like what we were hoping to see it was an unmistakable evidence that there had been either now or in the past was fluid flowing on the surface of Titan you could see a drain into this region here which this is for all the world looks like a shoreline we've known we've been able to find out since that this region is about a hundred metres higher than that so at least the the geometry works out and then finally this picture is taken at eight kilometers altitude and then finally we came to rest the probe came to rest in a flat area in fact one of the dark regions that we were seeing from orbit it landed essentially on the Titan equivalent of a mud flat an unconsolidated ground that was wet with liquid methane and very likely made from the accumulation of material that had fallen down organic material falling down from the skies for like we don't know how long but it was it was thrilling to say the least this part of the mission reminded me of a Jules Verne adventure come true it was really a spectacular thing and very moving for those of us who were who were there but the bottom line is there were no lakes of liquid hydrocarbons we thought we'd see open bodies of liquid hydrocarbons we knew we had to be there that they had to be there the calculations said methane would condense even ethane might condense that of the the atmosphere at those temperatures and form liquid bodies and there were none and then things got really puzzling when the radar instrument on Cassini discovered that those vast areas those dark areas we see in the equatorial and mid latitude regions are covered with dunes okay miles and miles of dunes they're a hundred metres high they're about three kilometers apart they're longitudinal dunes you get these from by directional winds winds coming in from both directions sustained winds and in order to get dunes you need dry I mean you need really dry so I mean this is saying you know it was dry so we were really puzzled where were the the bodies of liquid hydrocarbons and then finally we got a view of the pole thanks to our inclined orbits and we saw something at the South Pole that looked like a lake and then two years later the the radar got really good views of the north polar regions here's just one of their many synthetic aperture radar instruments showing channels going into a body of this looks like the coast of Maine okay but this is a body that's filled with methane and ethane I mean they know that now we know that and and then over time this was taken in 2007 over time we've pretty much covered the polar regions of Titan and of course a large part of the rest of Titan and so this is the North Pole I forget in fact what's the latitude this is I think that's the 36 TS so this may go down to 60 or 45 I don't know but anyway all of these are bodies of liquid hydrocarbons and what I just showed you was taken from this region here so we know now that the poles are where the Hydra carve the liquid hydrocarbons have Titan on Titan if gone most of them most of the flick in the northern regions and we're just trying to put the whole story together as to why and how and so on but one thing now is very very clear that after decades of speculation about what might lie underneath the haze of Titan we now know and what we have found is an utterly remarkable place the only place the only place in our solar system where we have liquid organics ponded on the surface and lacing the atmosphere a place that it is that is exotic and alien but at the same time very familiar to us and a place that in all the solar system in its geological complexity and geographical diversity is rivaled only by the earth itself so we are greatly looking forward to three more years of the Cassini mission and we will be paying a lot more attention to to Titan because it has just been a fabulous adventure but despite all that if you asked me what was the most thrilling discovery that Cassini has made it has been what we have found capping the south polar region of the small moon Enceladus so there's a specular reflection of Titan so this picture is it's not meant to be a threat okay we're just trying to show you Enceladus is a very I mean I go and give this talk in England I got to make sure they you don't think this is like one of Dick Cheney's bright ideas or anything Enceladus is very small okay it's only 500 kilometers across and we suspected going all the way back to Voyager that there was going to be something special about this moon and I'm very proud to say that I put a statement in our space science review paper if anyone here as the scientist who's ever had to write a space science review paper about an instrument that was going to fly on a mission you know what that's all about this is just where you describe what your instrument is capable of doing and what your science goals are and I put in there that it could very well be that Enceladus was going to end up being the Europa of the Saturn system and I was dead right so anyway here we knew it was unusual because from Voyager we saw vast tracts of this moon had no craters on it when you see something has no craters on it you know that it's been internally active and yet it's so small how could it be internally active people were scientists were really trying to figure out between Voyager and Cassini how Enceladus could have been active they couldn't they really couldn't make all the numbers work out but anyway we found that in fact no there's no craters that's true invest in big regions there's no craters but there it's had an enormous Lee complex tectonic history with multiple generations of cracks deep fractures mountain ranges and so on so obviously something happened to it but but far and away the mother lode of discoveries that we have made on Enceladus happens at the South Pole where there is a region that extends down to about 55 degrees south latitude so that would be like Tierra del Fuego on the earth everything south would of that is this region we call the south polar terrain it is circumscribed by these mountain ranges and folds and it is characterized by these four very prominent fractures that we affectionately call the tiger-stripe fractures and the make it might the South Pole the exact South Pole is about there and this region is also characterized by heat okay we have found incredible amounts of heat coming out of these fractures and here is another look taken three years later during the equinox okay so you could just get a bull's eye view of it and you can see that it really is a region that is very unique and separate from the rest of Enceladus and when we put Cassini in a position to look in the direction of the Sun over the South Pole which is we did this deliberately this is eight whoops this is a geometry that highlights fine particles this is what we saw we saw Jets of fine icy particles extending hundreds of kilometers above the surface and actually they form if you process this image in just the right way they form a gigantic plume that extends for tens of thousands of kilometers into the space around Enceladus Cassini has flown several times through this plume by design once we found it this was the benefit of our orbital tour once we found this we you know rejiggered our plans to make sure that we flew through this plume and of course in mission extensions we've since paid a lot of attention to Enceladus so we have good compositional information about this plume and we found that those Jets are accompanied by water vapor but also the particles are salty with the salinity comparable to the Earth's oceans and that tells you they are salty water droplets that are frozen and they are accompany the vapor has trace amounts of organic molecules small amounts of ammonia and carbon dioxide and so on all compounds that are considered important for the origin of life and images like this as well as images like this that we've taken over time and images like this which is one looking in the direction of Saturn and you could see the the feet of the of the the Jets here all of these have allowed us to survey the South Pole and determine the locations of these Jets and determine their three-dimensional configuration these Jets we now call we know it's a good term to use I mean we're confident now they are geysers okay and it strongly suggests that they're geysers and that they erupt from an ocean located under this the ice shell with channels that lead from those major fractures all the way down to to an ocean and we know this now because we've conducted what are called gravity done gravity measurements so it's not just inferential we know now that the structure in the south polar region looks like this you have an ocean that's about ten kilometers thick above the core it's in contact with the core and this ice shell here is about 35 kilometers thick and we just recently got results that indicate that there's probably even a global ocean though the global ocean itself would be thinner than the ten kilometers here so we are now very confident that Enceladus presents to us an environment where prebiotic chemistry and perhaps life itself might be stirring and in that case it's not completely crazy to say or suggest that there are microbes snowing at the South Pole of Enceladus and maybe even making it into the e-ring unfortunately Cassini is not equipped to tell us whether life has ever gotten started on Enceladus but I don't think I need to state it too strongly that should we ever make such a discovery that if we ever find that Genesis had occurred independently twice in our solar system then that means the spell is broken and the existence theorem has been proven and we could safely infer from that that life was not a bug but a feature of the universe in which we live that it was commonplace like black holes and galaxies and so on and that it had occurred an astronomical number of times in the 13.8 billion year history of the cosmos and I think that would be a final answer to probably the longest standing question in human history and the kind of scientific discovery that could extent could change at least in the scientific community could change a great many things and because of all the thrills and excitement that this moon has afforded us I am hanging on to one very fanciful notion that somewhere someday in the far future our descendants might voyage back to the Saturn system to visit the Enceladus interplanetary geyser park in a spaceship not unlike the Starship Enterprise and so Cassini continues to orbit Saturn it will do so for another three years and it continues to return one exciting discovery after another and deep insights into our how our cosmic neighborhood came to be and when it is all done it will surely go down in history is one of the most profoundly scientific interplanetary missions that we have ever flown but more than that the story of Cassini like the stories of all all our interplanetary explorations over the last five plus decades has at its heart been a story about longing about a longing to know ourselves to understand us and despite all the glorious scenes that we have seen over the last ten years there is an image that speaks of this longing better than words ever could and it has a bit of a backstory and so I want to tell that to you now back in the 1980s I had the pleasure of hitching a ride on one of the greatest adventures of exploration ever and that was the Voyager mission to the outer solar system I was right out of graduate school and I blessed the day that the head of the imaging team added me as a member it really set the direction for the rest of my life and I've had a pretty cool life and I had the pleasure during those years of coming to know someone I'm sure you've heard of and that is Carl Sagan and of working with him and others in planning and executing the famous pale blue dot picture of Earth that was taken in 1990 by Voyager 1 from beyond the orbit of Neptune as called this is not well known but as Carl had described it in a proposal to the Voyager project to convince them to take such an image because they did not want to do it the idea was to take a picture of the earth and I quote awash in a sea of stars now if you remember the actual pale blue dot picture that's not actually what it looked like and it turned out not really what we had envisioned there were no stars and unfortunately it showed the earth sitting on top of a beam of light that had been scattered in the optics of the camera but none of this really mattered because it was what Carl had to say about this picture and the way that he romanced it and turned it into an allegory on the human condition that has forever since made its name pale blue dot synonymous with an inspirational call to planetary brotherhood and protection of our planet and protection of the environment well since the very beginning of my tenure is the leader of the imaging team on the Cassini mission I had it in my mind to do this picture over again only make it better and it occurred to me along the way as I'm thinking when should we do this how should we do this and so on how great it would be if we let people know in advance that their picture was going to be taken from a billion miles away right in ever since the original pale blue dot picture there have been missions who've done it they've been lots of pale blue dot pictures taken from you know on way to Jupiter or in orbit around Mars or on the surface of Mars and in every single case the picture was taken and then two days later two weeks later the mission people announced hey world we took your picture two days ago here it is and I thought well what a missed opportunity let people enjoy the moments when their picture is being taken and invite them to go out and at that time contemplate where they are in the utter isolation of their home planet in the blackness of space and appreciate the rarity that our planet is among the other planets in the solar system and marvel at their own existence in that of life on Earth and so it happened on July 19th of 2013 the Cassini cameras were turned to look back at Saturn Eddie as it eclipsed the Sun which made this event even possible to take another pale blue dot image of Earth and we sent out the word at the moment the picture is taken look up I'll look up think of all of us think of the Magnificent achievement that this interplanetary salute between robot and maker represents and smile and people responded exactly the way I had hoped many comments came in from people all over the world stating a feeling of unity with their fellow humans and here are just a few that I have to read to you this is from test somewhere she doesn't say where at the appropriate time I left the table at a restaurant and went to the parking lot I turned my face to the sky and I spent a few minutes watching and listening to what life on earth was like right there right at that moment what a feeling of connection and oneness with the miracle that is life on Earth this experience was beyond meaningful it was transcendent what a beautiful thing thank you and this is Phil in Tennessee it was 427 p.m. in hotend Tennessee my daughter and I hung a home sign on a tree in honor of the only home we've ever known and we smiled for the camera this is Sam somewhere in England mmm Phoebe aged 10 and I got the telescope out on the patio under a beautiful clear southern British sky we gazed upon Saturn reveling in the fact that a spacecraft was looking back on us she has lots of questions and at the appointed time I raised the glass of fine red wine she a glass of fizzy pop we said Cheers to Saturn to Cassini to each other then we smiled and laughed and waved and cheered and took photos of ourselves it was perfect and this one I really love mmm i this is Jolene from upstate New York I have been entranced by this project ever since I heard about it and was determined to join in the celebration however I never anticipated how emotional I would feel I stood on the edge of Lake Ontario in upstate New York with my son and his girlfriend I had forgotten to bring my cell phone with its that shows the location of Saturn so in the end we just spun in circles waving at the sky the thought that a camera was taking pictures from so very far away was just incredible we may not be unique we may be transient we may be only flying along on a dust mote but darn it for 15 minutes we were there we were aware and we smiled and so it was a great success and here's the mosaic I'm sure you've all seen it by now when it was taken think about this it was taken when many many people on earth were thinking about their cosmic place it is taken Saturn eclipsing the Sun this is the Rings seen in silhouette this is the ring the earring created by the spray from Enceladus this is the Moon tempest you've seen already and looking over the shoulder of Saturn in the distance a billion miles in the distance is our small little planet Earth and when examined even closer with our high-resolution camera on Cassini becomes the earth and the moon seeing for the first time as distinct objects from the outer solar system so as evidenced by your reaction there is something very powerful that we feel when we see our own little fragile blue ocean planet as it would be seen by others in the skies of other worlds and it is I think that startling uncorrupted recognition of ourselves as we are where we are that never fails to move us and it moves me to see in this picture the place where Charles Darwin and the Italian astronomer Galileo come face to face because it is a picture that was ultimately made possible by Galileo's first experiments with gravitation over four hundred years ago and it is a picture that absolutely shouts evolution I look at this picture and I see our distant ancestors stepping down from the trees and walking upright for the first time on to the African savannas and pausing to look back at the forest from which they came and I look at this picture and I see a species that is relentless in its pursuit of knowledge and brave and ardent in its longing to grasp the meaning and the significance of its own existence and finally I can't help but look at this picture and see the very very best that humanity has to offer we are without question the cruel and troubled and warlike inhabitants of one tiny little dot of a planet and we are reminded of this day in and day out wherever we look across the globe but it would serve as well to remember we are also the dreamers and thinkers and explorers who took this picture one world clear across interplanetary space to another and to be so small and reached so far is in the end what makes us the extraordinary citizens of planet Earth and this proud perspective is perhaps the greatest gift of all and the legacy left behind by Cassini and all its brethren interplanetary missions over the last half-century I say let's revel in it we deserve it thank you so thank you for this terrific talk are any questions yeah can we have the lights now because it's hard to see what powers Cassini you mean like after Newton I presume you mean is plutonium dioxide okay so we have our tea geez and then of course there's fuel there's still hydrazine fuel that we can use to you know do trajectory correction maneuvers they're called and so on but really the reason why it's gonna end okay we have to do a little bit lower on the lights the reason why it's going to end is because nothing can last forever everything's going beautifully this has been a spacecraft that was built to last we never had a single problem with it it's really blessed but you know we've it will be by the time it's over okay I will have been on this mission for 27 years okay I'm surprised I'm not in a walker so so you know we and we're ending it at a really good time we arrived at the height of southern summer and we're going to terminate it send the spacecraft into the planet at the height of northern summer so between the two hemispheres we will have seen a full seasonal cycle on Saturn and throughout the system that will give us insight into seasonal changes and so on and you know by that time I think we will have traveled with Saturn for half it's more than half its orbit so you know it's been a good ride I'm not complaining with sources in regular spaces firstly the old bones law formulation is real hokey but there's something there if you plot it a lot exactly it looks like triggers and you see that not only the solar system's been in the Saturn system and the Jovian system my new steel plant and you know everywhere repair the system that we could see another some of these exoplanets if there's four in a system it's hard to tell it's basic but at least in the local ones we're seeing this pattern I have a feeling the answer to your question is gonna be I don't know but well okay so I'm largely ignorant of what's happened since there are people who spend their time thinking about this I could take it yes you know but I I don't really want to say because I don't know for sure I mean you know it's it's all I mean it's nothing hokey or you know crystal energy or anything it's gonna be gravity and and I you know probably the zones over which bodies are you know dynamically dominant and you know the further you get out these are just you know basics like the further you get out the larger the orbit the more area volume you have to sweep up if you're a planet or a growing planet that's accreting material so you could imagine that the further you get the larger your zone of dominance and we see that in our solar system but I mean more than that I can't say okay good if she agrees that all I know it Cyclops org oh okay I wasn't gonna do this because it seems so trashy but there you go you must have read that in the National Enquirer because I've never I've never heard that no in fact it's just the opposite you know we we there are various lines of reasoning that pointed to the rings being maybe only a few hundred million years old and and now you know with everything our understanding has gotten richer and things have gotten more complex and now it's very likely that there's like the beer in could have a lot of mass in it if it has a lot of mass in it and we're hopefully going to measure that during the very last orbits of Cassini when we're going to be and really gonna be in polar orbits and going within the the between the D ring the innermost ring and the the planet mmm and hopefully these orbits are gonna allow us to measure the mass and the Rings better than we now know but if the Bering has a lot of mass in it it's not out of the question it could have been around billions of years okay so so hundred years no one's ever sent a hundred years maybe you maybe you remember one hundred million years I do that all the time I get million thousand I get it all back there like Oh tidal disruption is also a what's the word I want a major contender and in fact a new model came out by Robin can up in Bill Ward I think he was part of this is that what you're referring to are you kind of like gently getting to that no okay I thought this was maybe like a leading question there is a model that said that you know okay I got to back up a little bit in in the models I guess thinking that people have done about the formation of satellite systems I think even in looking at exoplanets and looking at those systems it's not out of the question that there could have been for Saturn a lot more Titan sized objects and if they're close they get tidally swept up into the planet so one idea was there could have been other Titan bodies you know other Titans they get swept up into the planet and then next to the last one because the last one is still there then next to the last one could have been tightly disrupted if it had been a differentiated body with a core and a nice shell around it which at that size it most certainly would be the ice shell would be ripped off first and it could form a ring system and I forget what happens to the core in this model but in any case that is basically a tidal disruption model and that actually solves some problems that the you know smashing up moons idea does not so that's a major contender to I just talked about it because it led me into my little movie I love my movie it's corny but I love it everybody always laughs at it so that's good yes oh I'm sorry you yeah I thought I said that it's six waves it's sick it looks okay first of all be aware that you're being fooled it's wrapped around a sphere and if I could take it and stretch it out you know just have it be on a line it would be almost like six sinusoids right you know right in a row so it's not really there's no real straight sides but it's the straight sides that freaked everybody out so and it's stable because all meteorological phenomena in this giant planets are stable because as I said there's no friction well it really depends which ring you're talking about the a the B of the C ring in the B ring it's almost purely chaotic and that's a process we I'm proud of this because I did a major paper on this so of course I'm gonna tell you it's the right answer but it's actually no it was an idea of my thesis advisor who's a brilliant guy and he you know said try this and we tried and it looks like it worked it's a process called viscous over stabilities and it arises because oh this is complicated so I'm not it let's imagine you have a system you know it's a system of particles you could imagine it being the surface of a body of water though and you could get you know waves in it that you know go pass through each other and you know if it were with particles you can actually get them to collide and compress and so on and create create ringlets like that that's how you get the chaos we think there's lots of these viscous over stabilities of a great variety of wavelengths and they're all passing through each other and interacting with each other and dense parts of the Rings that things get nonlinear so that's the B ring the C ring we're not quite sure there are things that are there we don't quite get there's plateaus where there's you know they're fairly broad and there's particles are not confined gravitationally we can't find any resonances but yet there they are this you know this plateau I've said Plateau it's just a region where the particles are dense and it's sharp edged and it's there and it stays there and it seems to be stable we don't have an idea of that but that a ring as I said is punctuated by all these resonances with moons so it's got lots and lots and lots of density waves and bending waves and so on oh you talking about the Wiggles that why I answered the question you meant me to ask what's next with the planet why are they there I'm not really let's take this let's take this are you talking about the bending waves where I said the ring was corrugated that's external moons that have a resonance in the Rings okay so that means every three times the particles go around the moon goes around once and that's a configuration where the moon can transfer easily its angular momentum and energy to the particles so they do crazy things like make waves and you get a bending wave where the ring gets corrugated when the satellite is inclined you got to have a vertical component to the gravitational interaction so the satellite has to be on an inclined orbit for that okay if NASA gave you a million dollars to go to Enceladus and figure out if they're microbes there do you or other Earthlings know how to do that is anybody planning to do that good that does good yes we are planning to do that but but NASA is not gonna give us a billion dollars that's the the sad that's the bad news the good news is we are planning it there's various ways well first of all okay you you gave me the opportunity to say I'm and doubtedly gonna get some people upset but I have to say it because it's the truth and selling this is the best place to go okay we have a whole program going to Mars and if you just checked off you know the things you want to see if there's life there Mars has none of them I'm not kidding no liquid water no organics okay it's we doing Mars be mean not that it's not valuable don't get me wrong but if we're doing Mars for historical reasons maybe even hysterical reasons Europa Europa I say let's just assume your rope has got it it's got the ocean it's got life but we have yet to see if it's got a way to access that easily the thing that wins that makes Enceladus wins is because it's accessible it's got this ocean we already know its composition at least you know to the extent that Cassini could measure it because it really could only measure compounds as big as benzene so c6h6 that's it but we know it's got carbon it's got all the elements we need it's got its in contact with a core that means it's got the chemical energy that methanogens and not you know beep microbes like that would like it's got everything and it's gushing into space so we know already with Cassini all you got to do is fly through the plume I used to be fond of saying all you have to do is land on the surface look up and stick your tongue out and you've got what you came for but landing then we would need a billion dollars and we're not going to get it so we're gonna fly through the plume there is some talk if we could do it you know if NASA really gets their act together and gets excited about this we could even do a sample return seven years their fly through the plume with the kind of stuff that they used on Stardust to collect you know material and bring it back we're certainly planning in the near term hopefully our proposal would get selected to collect to do in situ measurements with a better with better instruments that are more capable so you know there are certain things you can search for you you guys don't know this right chirality and you know patterns among your amino acids and so on that we're hoping to do so but it really is you know I mean all joking aside it's the most accessible place to go and we really it's the go-to place now for astrobiology nono just money it's you know the bucks there's no bucks it's a lot of well I'm excited about it or you know then okay go go for it get us some money oh okay so Titan is bigger first of all if you have a body that's bigger if it had any volatile material for example well let me just say it retains it can retain an atmosphere Enceladus probably is not big enough to retain an atmosphere so Titan has an atmosphere it could have been outgassed and I mean that the answer is how oh you're in your question is really how it got that way Enceladus you've just got to remember and sell it assist tiny it's really tiny I guess I forgot to mention the reason why it is the way it is is because it's being flexed by a resonance with its next-door neighbor to two satellites over dyani so it's got tidal energy that's being forced into it and has been for as long as that resonance has been in play and that is what has melted the water and created the ocean and then the organic material you know I say let's take it as ground zero the organics are everywhere really they're everywhere so you know they are there on the ocean in the ocean of Enceladus the question is have they done anything interesting

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Published: Tue Feb 10 2015