 So, let's get to our program. So, Trina Ray received a BS in physics astronomy option from Cal State Northridge in her master's degree in astronomy from San Diego State University. She has held many positions on Cassini during her 21 years on the mission. She's been there the whole time, including instrument operations engineer, science systems engineer, and currently is Cassini's science planning and sequencing team deputy in the Titan Orbiter Science Team Co-Chair. She was one of the key strategic planners of the Grand Finale mission. So, we've got just the right person to tell us all about the mission and about what it's been doing on its last orbits of Saturn. So, please welcome Trina Ray. Okay, so Brian, I've unmuted and I've started video. I think I just share screen and I'm golden, right? Indeed, we're golden, thank you. Okay, share screen, and then I'm gonna open up PowerPoint. Right there, first slide. All right, how does that look to you guys? Looks perfect, thank you. Excellent. Okay, well, as you can imagine, it has been a crazy, crazy week, the last couple of weeks for Cassini. So, what we're gonna do is just do a little bit, you know, not everybody's completely familiar with the mission, so I'm gonna just do a little bit of overview of the mission and then sort of step you through the last ridiculously exciting 22 weeks of the mission and then finish out with what happened last week. So, the Cassini spacecraft is actually two spacecraft. We partnered with the European Space Agency. They built and operated the Huygens probe, which landed on Titan and the Cassini orbiter. Let me just see here. Brian, if I use my mouse to point at things, can you guys see that? Yes, it looks like your cursor is pointing at things. Excellent, I will use that then. So, on the left is the Cassini spacecraft. You can see down in the lower left-hand corner or just down around the probe, people so that you get a sense of the size. Spacecraft is quite large. It's 22 feet tall. The high-gain antenna, which is the giant white dish at the top, which is the radio communications link with the spacecraft that'll play an important role in what we're talking about later, is about four meters in diameter. And you can see that almost everything that's important about the spacecraft tucks in behind that giant high-gain antenna. When we launched, we launched with, we weighed about six tons when we were fully fueled. We had about 2,000 pounds of fuel and we're down to 10 plus or minus 20 left in the tanks. And we are absolutely positively on fumes, and that's one of the reasons we had to dispose of the spacecraft. We also have radio isotope thermoelectric generators. We started out with about 875 watts at launch and now we're down to less than 670. I need to update that slide. And we also have a gigantic, huge massive 0.5 gigabyte recorder. There was a time when I thought, wow, you're never even gonna fill that up. But of course, the appetite grows to the resources that you have. All right, the spacecraft itself has, oops, hey, don't go to, don't get ahead of yourself PowerPoint. The spacecraft itself, the orbiter has 12 instruments. Those instruments are collected into two sets. They're either the optical remote sensing set of instruments, which are sort of all four of the cameras, both the infrared, ultraviolet and the visual and infrared mapping spectrometer. They all look together, wherever the spacecraft is pointed and we have to move the whole spacecraft to take a picture of something. We also have what are called the magnetospheric and plasma science instruments. These are all the instruments that are interested not in taking a picture of something far away, but in sampling something, the environment that the spacecraft is embedded in. You know, what is the, how many dust particles are hitting the spacecraft? What is the strength of the magnetic field right here where the spacecraft is? So these instruments work together to sort of want to explore the local conditions and the cameras usually want to look at something far away. We also have two microwave instruments that uses the high gain antenna. So for example, if you take the high gain antenna signal and you send it back to the earth and you happen to put the rings of Saturn in the way, well, then you can learn about the rings of Saturn. That's called radio science. And we also have a radar frequency on board. So you could, for example, blast the surface of Titan and get a radar reflection and learn about the surface of Titan. All right, we launched in 1997 from Kennedy Space Center. And this is a little launch video here. We're not gonna play the whole launch video, but I wanted to give you a few seconds of it there. This was a beautiful time-lapse photograph. T minus two. This was a Titan 4B, which is the largest rocket. Oh, that has got to go. That has to go as well. Nine, eight, seven, six, five, four, three, two, one. And liftoff of the Cassini spacecraft on a 30-mile trek to Saturn. So just about 20 years ago. The program is in, the whole program is in. And it went behind a cloud deck and the cloud deck lit up and a lot of folks thought that the spacecraft had exploded because it was like, oh my gosh, you couldn't see it. And it was flashing. And then when it erupted from the top of the cloud deck, everybody was just cheering madly. All right, I'm gonna stop that movie now. So we toured the inter-solar system. This was to get our speed up to get to Saturn in a blistering seven years. We went by Venus twice, the Earth, and then finally Jupiter. And we arrived in Saturn, July of 2004. All right, go to the next one. PowerPoint, do not give me SNP today. I am not taking SNP. Okay, so when you take a spacecraft all the way out to Saturn, what are you going to study? Obviously, you're going to study the rings. They're incredible. You're gonna study the planet itself. You're gonna study all the icy satellites, but in particular, you're going to study Titan, which is the largest satellite of Saturn. It's larger than the planet Mercury and has a thick atmosphere. Absolutely worthy of a talk all on its own. Vivian and Brian, you can call me up in a couple months and I'd be happy to give a talk just about Titan. We have, of course, plunged the spacecraft through the ring plane at SOI, and it was in the same place where the voyagers went through. And there's a giant magnetic field around Saturn itself. So those are our five disciplines. The planet, the rings, all the icy satellites, Titan is special and the magnetosphere. And by the way, where we plunged the spacecraft 22 times is right here in this gap, right near the I and D ring. Okay, so we launched in 1997 and we got to Saturn in 2004. Remember Saturn orbits once every 30 years? That means the seasons on Saturn last about seven years. When we arrived in 2004, it was basically Northern winter, think of it as like January 12th. We arrived roughly January 12th of Saturn's year. We had a four year prime mission. That didn't even get us out to spring. So we asked for an extension to get us out to the spring equinox. And then once we completed that two year extension, we asked for a seven year extension to get us out to the end of, to get us to the next season, which was summer, the summer solstice. And then we had a completely separate conversation with headquarters about how to dispose of the spacecraft in these very exciting proximal orbits, which you'll hear about tonight. So this is where we are now at the end of the mission. The mission ended last Friday and I'll be telling you all about that. So one of the reasons people ask us if the spacecraft is healthy, why are you disposing of the spacecraft? And the answer is we have to. We are literally running out of fuel. We are on fumes every time we do a maneuver. In fact, every time we've done a maneuver in the last year, it was like, well, maybe today when we step on the gas, there will be gas and maybe not. We had a backup plan if there was no gas, we could use our thrusters to move the spacecraft. But both Enceladus and Titan are very astrobiologically interesting. And we had to dispose of the spacecraft in such a way that we would not contaminate those. So it was very important to do that. Enceladus has got a thick ice shell but then a hot ocean that touches hot rocks and has thermal vents with hydrogen, which is the food for microbes. So of course we can't go crashing into Enceladus. And Titan is one of the most earth-like bodies in the solar system with standing bodies of liquid on the surface. So we can't go there either. So here's the seven years of our solstice trajectory. You can see that it's really just a ball of string there. If your eyes are good, you can see the Titan orbit because we fly by Titan so often. Here's a node right there. And as it comes around, here's a node right here. That's obviously at the Titan orbit. The F ring of proximal orbits in comparison. Here are the ring grazing just on the outside of the rings. And then here are the grand finale proximal orbits on the inside. So we had the ring grazing orbits. Those are the white orbits. We had 20 of those. And then we had the grand finale orbits. We had 22 of those. And you could see those grand finale orbits plunge the spacecraft right between the planet and the rings. So I wanted to give you some highlights from the ring grazing orbits. This is when we were on the outside. The ring grazing orbits were really focused on being able to take some of the highest resolution images of the rings of Saturn and just really try to get some close-up images of some of the small moons that are embedded in the rings. These are the three we're gonna talk about. Daftus and Atlas. Pan is in the anky gap. Daftus is in the keeler gap. And Atlas is on the outside of the A ring. We never would have imagined we could have gotten these images in a regular part of the mission. But these last orbits allowed us to just have incredible, incredible resolution on these little moons. So this is a very small moon here. Pan is just, you know, is just I think a couple of miles across, I think. Maybe, oh boy, on another week, I would have this data right at the tip of my fingertips. But this week, numbers are escaping me. Pan, pan, pan, oh, very small. Okay, it's a very small moon. It's in the anky gap. But you can see here that even with this ridge of material around it that is soft and fluffy, you can see that there have been impacts that have left a mark, which is just incredible that it maintains that structure. And by the way, look at this crack here. This crack that goes underneath, and you can see the crack emerge on the other side. And here's a landslide of this soft material. Within hours of this picture hitting the ground, one of our scientists set out this cute little ravioli. Cause you know, we work with fun people. Daphnis is a little moon that's in the Keeler gap. And Daphnis, when material goes by Daphnis, so at the top of the image is headed towards Saturn. And at the bottom of the image you're further away. So all the rings, particles for Saturn, they all orbit sort of in their own, the ones closer to Saturn orbit fastest. So all of the particles to the right have already gone by Daphnis and been disturbed. And here Daphnis is going by the particles to its left and disturbing it. But when you colorize this picture, you get a much better view of it. And look at this little material, this little stream of material here, that is just like almost a perfect gravitational capture of material from a ring. It's just fantastic. Atlas was on the edge of the A ring. And here you could see that the skirt of material is much larger and almost obscures the central core. Atlas is also one of these small ring moons. And we did a lot of looking at very particular things in the ring since we had the opportunity to do so. While Cassini has been in orbit, we've discovered what we're calling propellers. Remember, when you have something in Saturn's rings, the particles on the inside go by first. So they get disturbed and the particles on the outside get disturbed when the moon goes by. So they always have this little quality of that make it look like an airplane propeller. Most of the propellers are being named after famous aviators like Amelia Earhart. And we've discovered hundreds of these. We were able to get some of our closest images in the whole mission during those effing orbits. We also took the opportunity to look back at the Earth. When Saturn is blocking our view or is blocking the sun, we can actually take a picture of the Earth. And one of the nice things about this image is we plan these things very far in advance. We plan them literally months, months and months and months, even years sometimes in advance. And the software was never intended to tell you about the moon of Earth. So when the picture actually came back and somebody saw this little light pixel thing off to the side, somebody says, well, wait, is that the Earth's moon? And of course the meeting was over at that point as everybody pulled out every piece of software they had to try to figure out the answer. Within just five minutes, we figured out that that was in fact the Earth and the moon in that shot. And that was just a real pleasant surprise. Now of course there are challenges to these orbits. These orbits were some of the most challenging in the whole mission. That gap is something that we did not know about and there are dangers in the gap. There's dust and Saturn's atmosphere and we spent quite a lot of time, years in fact, understanding what we would have to protect ourselves from in the gap. So of course, you kind of have to understand how the spacecraft is going through the gap. So what's important is, okay, sorry, let me go back. This is a picture of the gap. Sort of everything we know about the dust is from this picture, which is just mind-boggling that we were, it's kind of mind-boggling sometimes when I look back at sort of what we knew and the risks that we took and what we ended up doing and our successes, but incredible. So that is a picture of what we know about the region. So here's what I was gonna say. There's two things to pay attention to. There's when you're crossing the ring plane and when you are at the minimum altitude and those are two separate things. One of them is the area when you are afraid of the dust and the other one is the area where you're afraid of Saturn's atmosphere. If we kind of look down from the North Pole of Saturn, it just so happens that the orbits were sort of cycling and they cycled exactly in time order. So you can actually take those two points on every orbit and you can actually put it in a plot, which of course, that's what engineers and scientists do. They put things in plots. So here you can see that the X's are the ring plane crossing and the pluses are the minimum altitudes for each and every crossing. You can also see that we've got a little Saturn down here and a dust ring up there and those aren't hard boundaries. You know, there's sort of a fuzziness to them that we need to explore. And so that's part of our efforts in trying to figure out what to do. So, all right, go forward a second. Why aren't you going forward? I don't know why you're not going forward. Okay, phew. Okay, so the ring plane crossing, we use that image to determine where we thought there was an actual chance of dust particles hitting us and we drew a line in the sand. And so the manager said, of course we're going to protect the spacecraft for those crossings. And we're also going to protect the spacecraft on the very first crossing. We called them shielded crossings and of course being the geeks that we are, that meant Captain America's shield appeared on the plot. And the very first one, because when you take a spacecraft into a place where you've never known the environment before, you want to be extra careful. All right, so what does it mean to be protected? Well, it means to hide behind the high gain antenna. You can see here in this little movie that the high gain antenna protects almost all of the spacecraft. All the critical components, the only thing is the magnetometer and the plasma wave antennas that stick out. So that means putting the high gain antenna in the direction of the threat, which meant the dust particles. All right, the second thing we had to be aware of in terms of risk was Saturn's atmosphere. And how do we learn about Saturn's atmosphere? We learned about Saturn's atmosphere mostly through occultations, solar occultations or stellar occultations. So we watched the sun or star drift behind Saturn's limb and then we figure out what is the density and temperature and pressure that the Saturn's gases must have been at to cause the starlight or sunlight to decrease the way that we saw that it did. And so we have a group that gets together. It's called the SAMWIG, Saturn Atmospheric Model Working Group. And they took all of the occultations, everything that we know from all the experts in the world and they gave us a profile of what is the density? And from that we were able to determine things like, what is the one bar atmospheric pressure? Where would the spacecraft be sure that it was captured? And also where would we have to be on thrusters versus wheels? So that is those four lines that have come in on the plot there. So you can see here that what we had was four very high flybys of Saturn where we were protecting ourselves from the dust and then the last five where we were definitely inside of Saturn's atmosphere a little bit and we had to be on thrusters. All right. So I just mentioned that these are the ones on thrusters. We had two other flybys on thrusters but that was for science. So we wanted to spin the spacecraft as fast as we could for the magnetometer. All right, I've already mentioned why we did this. We had to do a safe spacecraft disposal but when the scientists heard that we would be able to send the spacecraft in between the planet and the rings they were almost giddy with what science they could do that couldn't be done before. And we wanna talk at least about three very unique pieces of science. The first one is Saturn's internal structure. The magnetic field of Saturn is almost completely aligned with the rotational axis and of course if you ask any theoretician of magnetic fields and giant gas planets they will tell you that is impossible that the dipole should collapse on itself if they are perfectly aligned. And because we always had to orbit on the outside of the rings. So we were always passing high over the pole and on the outside we were never able to get close enough to let the magnetometer really get at the mag field tilt except in these orbits now where we're coming screaming in right over the North Pole very close and then right over the South Pole again. Also we were able to take the high gain antenna and point it at the Earth. And when we do that we have what's called a gravity measurement and we can measure very minute poles of on the spacecraft from mass inside of Saturn and we're able to get to Saturn's internal structure. So that is unique science. Never imagined we'd be able to get that but we were able to get in these last orbits. The other thing is, this is one of those tricky things. The mass of the B-ring, the mass of the rings is something we really should know by now but we've never had an occultation that can penetrate this B-ring here. And so we've never been able to get the mass of the B-ring but when you take the spacecraft in between the planet and the rings the rings pull separately than the Saturn. And so you're able to get the mass of the B-ring and once you get the mass of the B-ring you know the ages. Also I should mention on Saturn's internal structure it will help us understand the day. How long is a day on Saturn? And then finally, if we can use our ion and neutral mass spectrometer and slip into Saturn's atmosphere a little bit and do in-situ observations that's of course completely unique science to these orbits. And we can't ignore it. Some of the highest resolution observations of the mission and of course for that reason absolutely some of the most gorgeous. All right, so here you have 250 scientists, 10 instruments, 12 instruments. They all want to do things, you have 22 orbits. So we start asking, who needs what? Well, radio science, they say they need six to get at the internal structure. The magnetometer says they need four and before you know it we have everybody chiming in and we need 36. So one of the key responsibilities that I had when I came back to the mission I had left to take a part-time job and then I came back was to work on being the key strategic planner for the grand finale mission and the ring grazing and grand finale orbits. And so this was one of the key sort of nuts that had to be cracked was how are we gonna do this? And we actually formed a special team and we put them to work on this and they actually did come up with an answer. And this is a spreadsheet that you're gonna be seeing for the next 20 minutes or so because I'm gonna step through many of the orbits because I kind of want you guys to get a sense of just how exciting these last 22 orbits have been. It's just been like so crazy exciting. It's just been so crazy exciting. And I kind of want to share sort of that with you guys as we go along. So here for example, you can see the six radio science ones right there 273, 274, 275, 7,880 and 284. Here's the two mag ones. And then of course, when you had 36 needs and 26, 22 flybys you had to learn how to share. So you could see almost every one of these is has some sharing capability. All right. So the highlight of the grand finale orbits let's step through it. So the very first orbit was rev 271 and that happened on April 26th. Again, remember this was that first one. So we had to have high gain antenna to RAM but we were doing Saturn observations on each side. So the first thing is the dust. Okay. This is what we expected. This is what we got on an F ring, a ring grazing orbit. You can see the white line here. Okay, so what was, you don't start yet. So what was that? That was little dust particles hitting the high gain antenna being vaporized and then that is being picked up by the radio and plasma wave spectrometer. Okay, you can see the ring plane crossing clearly. The intensity grows at the ring plane crossing. You could see there's tons and tons and tons and tons of hits. So this is what we're expecting. This is what we got. And as you could tell here, finally the scientists had to put an arrow so that you could like see the ring plane crossing and you know, you can hardly even hear anything hitting the spacecraft. In fact, when I went into the meeting, I love telling the story. This meeting was packed, the very first meeting after the flyby and the scientist who is the expert on the dust looks around the room and he says, there are more people in this room than there are dust particles that hit the spacecraft. So it turns out that the dust environment is quite benign and which is great for us. Cassini didn't have to be worried about anything in its remaining orbits, but also it's great for any other spacecraft whoever wants to go there. Okay, go forward. Yes, go forward. I don't know what your little, you know, PowerPoint is being stippy. Okay, so we also got a wonderful, a wonderful sort of noodle down Saturn because we were, this is the closest we'd ever been. And starting at the North Pole, here's a little animation. We were just taking pictures as fast as we possibly could. And then right here, you'll see the spacecraft turn and go high gain antenna to RAM, which was that protective maneuver because remember this was the very first one, high gain antenna to RAM. And then it finished up the noodle. And then here is the noodle right there. We started at the North Pole. Here's the hexagon. Here are things that every expert in the world when they saw these says, I have no idea what these are. These little white puffy clouds are they thunderstorms? What are they? We don't know. Isn't that fantastic that literally the world experts watching this movie and they're saying, I have no idea what that is. That's a great place to be, by the way. Let me play that movie again because that movie is so awesome. Over here is like the reference of what you're looking at. And over here is the images. So you're at the top there. Right now we're passing the hexagon. We're gonna see some of these little clouds. Highest resolution images of Saturn ever. Up to that point. That's just crazy. Okay, go to the next one. Boy, you know, all right. You are being very picky today. Okay, so the very first flyby, of course, giant smiley face. The magnetometer flyby is one where you could see that we're spinning the spacecraft like a platter. This is so that we can get as much high magnetic signal on all of the detectors of the magnetometer as possible. And it needed four of these. They need to come in sets. You have to orbit around one axis and then around another. A nice thing about that movie is it also shows you which magnetic field line you're on. Okay, boy, just every time I hit spacebar, it wants to replay the movie. So the magnetometer flyby on thrusters went just fine. The radio science flyby now was a little bit different. Here we have to be, we have to be high gain antenna to ram, or I'm sorry, high gain antenna to Earth. But we still want to be spinning for the magnetometer, but they worked it out that that was okay that they could share those. And then you can see here as we're plunging in between the planet and the rings, we actually get an occultation. The shortest, fastest, closest occultation of the mission. And we did this six times. And you'll see it coming up here. So that white line there is showing you the high gain antenna radio signal connecting off to the Earth and the distance. And then as we go right in between the planet and the rings, from the inside out, you get to see the rings. Now, one of the nice things about this, which people don't realize, is that a Cassini is a spacecraft where you take the data and you put it on the solid state recorder and then you play it back. So nine hours every day, you're playing the data back. 15 hours you're off taking the data. But for a radio science occultation, the receiver, the actual instrument is on the ground. And so you can actually see science in real time. And that is not something that you get to do very often. And so that's a gift when it happens. And so there were six of these. And I was like a drug pusher or something or a proselytizing constantly. Everybody on my team must go see this happen in real time. It doesn't matter if it's five a.m. or two a.m. You must go and see this happen in real time. And so what you would have seen had you gone to the room, here are the rings of Saturn. And so here's the thick part of the rings of Saturn. Here's a thin part of the rings of Saturn. So in optical depth, something that is thin, right, is a low signal and something that is thick is a high signal. But remember for radio science, we're sending a signal through. So when you have thin rings, the signal gets through easily. And when you have thick rings, the signal has a problem. And so here you can see the Cassini gap, right? Right there, the signal gets through easily and then you're back into the rings. And so when we went, here is in fact, the C ring. Here's the thick B ring, the Cassini division, right there in front of your eyes. In 20 minutes, you could see the rings of Saturn appear before your eyes. And it was truly glorious. I will treasure every one of those memories. The radio science team also has a very nice tradition where they take a picture of the screen and they have everybody in the room sign it. And so they're, see yours truly, Radio Science Emeritus. Scott was there, he's the deputy project scientist. Assam is one of the main scientists. Shortest, closest, fastest ring alkylation of the mission. Ah, what a gift. So there were our two radio scientists. We had three. You could see here that not everything is a smiley face. We did have some problems with the Deep Space Network antenna from the European Space Agency. This is hard, right? This is hard and it doesn't always work perfectly. But we didn't lose everything, but it was just degraded. So it doesn't, it's not a frowny face, but it wasn't a smiley face either. As you can see here, we're headed into some really great rings observations. Remember there was those four, one, two, and then this one here, three and four, where we had to go high gain antenna to RAM. Here are just some of the incredible, incredible ring observations that we saw. You could just see the structure of the rings, the bending, bending waves on top of bending waves. The plateaus at the edge of the A ring. Just, you know, it's just, ugh. I remember at SOI, Saturn orbit insertion, when we got these incredible high resolution images thinking, well, that's the best we're ever gonna get. And then to have 22 orbits was just crazy. We did also have another problem on one of those where we lost a lot of the downlink. We did have the very highest, most important data was on a dual playback, so we did get it. So again, not a frowny face, but not a smiley face either. All right, we did have another Saturn noodle and a couple of more radio science passes in there. So radio science, radio science, Saturn noodle, those all came down well. This was a nice ring image that came down. These plateaus in the searing we've known about for quite some time. And we can, we absolutely, you can see here, we can see structure. So it's not like we can't see, it's not like it's, our resolution isn't good enough. But we've done some really nice analysis on this to see there is in fact long strings inside of these searing plateaus that are just quite a mystery. Oh, so there were our two rings ones. And now we're headed into, you know, we're about halfway, let me go back one. You know, we've gotten, here we've had two magnetometer ones we're about to go into the next two. And so, you know, people are very interested in what the magnetometer has to say. And the, you know, the magnetic field again, as I mentioned, is surprisingly well aligned with the planet's rotation axis. And what they were telling us about halfway through these proximal orbits is that the tilt is much smaller than 0.06 degrees. Which is just, I just, that is so puzzling. Even the PI of the magnetometer team is just, you know, that is much smaller than had been previously estimated and quite challenging to explain. And I'm really looking forward in the next six months to the magnetometer team having a good answer to this so far. Also, we had a lot of analysis from the gravity and Saturn's interior is quite a bit more puzzling than we thought. All of the early analyses was hard to do and they couldn't figure out what was going on. They sort of tried every model of Saturn that they knew about and they were all failing. And so, you know, now they're trying crazy things like rotating cylinders inside of Saturn to try to see if they can duplicate the signal that they've gotten over these last, over those six great orbits. And remember I told you the mass of the V-ring? I said, once we knew the mass of Saturn, we could tell you the mass of the V-ring, but if we're having problems with the mass of Saturn, it's gonna take us a while to get the mass of the V-ring as well. So we made it through the last magnetometer ones and now we're headed into these cold orbits. As you could imagine, when you're plunging the spacecraft in between the planet and the rings, Saturn is gigantic on one side and the rings are gigantic on the other side. So there's almost nowhere that you can point infrared radiators that they will be cool because there's something in the field of view that is warm and you can't cool down. They have to be pointed to deep space to become cool. But there was important things to be done. So we did sort of sacrifice prime science at closest approach so that we could be cool and do some outbound science. Of course, we were well rewarded for that. This is the Southern Aurora. Here's the planet itself. This is Saturn. These are stars going behind because this is a long-term exposure and you could see this little ripple along here. And also it's kind of nice as you see the stars as they get close to Saturn, they get deflected by light bending them in Saturn's atmosphere. All right, so we got our cold Aurora orbit and now we're heading into these last five where we're skimming through the atmosphere. We had done a lot of thought about how to prepare ourselves for this. And we didn't want to be in a position where the atmospheric experts, the Samwick folks were telling us that they know things to about a factor of three. So everything was, you had to sort of multiply by a factor of three. If you wanted, for example, to be using the thrusters at the best of their capability, say 70, 80, 90%. Well, then you would have to shoot for like 30% so that if there was a factor of three, you know, you weren't out of the water because if you had gone for 70% and it was a factor of three that'd be 210 and you'd be dead. So we were very happy when we had our very first passage. This is the report from the project manager successfully completed, you know, this passage was the first of the crossing were briefly passed into Saturn's upper atmosphere. The ion and neutral mass spectrometer was prime and it performed the first ever direct sampling of Saturn's atmosphere. We were all happy. The torque was higher than predicted, which was good. We had shot, we had been shooting for 10% and we got about 30. So that was exactly what we had been afraid of that the atmosphere was much thicker than we thought but we had prepared ourselves well. Okay, we didn't know what was gonna happen. What if the atmosphere had come in quite a bit thicker? So we were ready to do a pop-up if we had to. We were also ready to do a pop-down if we had to. And it turns out we needed to do neither of those. We just were perfect, just like Goldilocks, perfect all the way through. And so then in one of these orbits, we had a beautiful inside-out movie taken of the rings of Saturn as we went through. It was gorgeous. It was fortuitous. It was that other cold orbit, actually. We were able to capture that. Okay, again, you're not forwarding unless I click this, fine. We also were able to complete the family portrait. We have from Saturn's orbit, taken pictures of almost everything but we had not taken a picture of Neptune. So we went ahead and took a picture of Neptune so that we could complete the family portrait. And then there we were headed into the last couple of orbits. Very exciting. The ion and neutron mass spectrometer was doing its work and these were just clicking off week after week. On the very last day, we did a mosaic of Saturn and its rings. We also took an image of Titan. It was called a Titan meteorological campaign. It's one of the last ones of the mission. We also watched Enceladus as it was setting behind Saturn. And we did a couple of propeller and Peggy images. The nice thing about this from somebody who's been on the mission for a long time is that it's a little bit of everything, right? We've got Titan, we've got the rings. We've got Enceladus. We've got a mosaic of Saturn. And of course the maps instruments are constantly taking pictures. And I actually wanna kind of go out of PowerPoint for a second and bring up, since this has now happened. Here's the last picture that we took of Titan. Here is the last Saturn mosaic that we took. Here is a visual and infrared mapping spectrometer image of Saturn in just a few hours before we crashed. And this is exactly the location on Saturn that we crashed. Here's the Enceladus movie, Enceladus setting behind Saturn. And then here is the very last image that Cassini ever took of Saturn. And you can even see the rings here in the distance. Let's see. And this is a very charming cartoon that I think I really like. So I put it in my presentations now. It says, so Cassini, I hear you're retiring in September, 2017, congrats. How do you wanna celebrate? Maybe do lunch with me in all my moons. Nah, I'll just go barreling straight into your atmosphere, learning as much as I can before I'm crushed to death and vaporized in spectacular whirling inferno beneath your mysterious stormy clouds to which Saturn has its reaction. But then the final panel is, that's awesome. And with that, I will take questions from the audience. Brian, how about, now, do you need me to stop sharing? What should I do? Yeah, why don't you go ahead and stop sharing and that will be for you. Sounds good. Okay, well, we've got one question that's up here and hopefully a lot of other people will add some questions here. There's a lot of really cool stuff here. This is really great. So Barry asks, the images appear black and white. Are there any filters used for these images? And I guess that's kind of a basic question of, how do you end up getting the color images? What is that? So that is exactly correct. Every camera that has flown into outer space is a black and white camera because that's how you get the highest resolution. And then you put filters in front of them to create color images. The filter wheel on Cassini is, I guess I should say was, the filter wheel on Cassini had, I think nine or 10 filters. Obviously, we had a red, green, blue filter so that we could get color images that your eyes are used to, but we also had a methane filter to see down to the surface of Titan. We had an infrared filter. We had a clear filter and we had a filter spot in the wheel that had nothing in it. So we had all of those. Polarizer, we had a polarizing filter. So yes, the pictures are black and white until they're processed. Okay. Well, Barry says thank you. So we're waiting for a couple of other questions. So what was your most memorable moment during the mission? My most memorable moment during the mission, I would say there's twofold. There's a moment that's technical and then the moment sort of that's more personal. That the technical moment was a moment of fear. It was a Titan flyby, it was T-13 and it was a flyby that was very important. In fact, it was so important. It was a flyby where we're going right across Xanadu with the radar instrument. And it was so critical that data that we had made a plan to have a contingency if something were to happen and we weren't able to get the data back. And on that morning, something happened and the spacecraft had been hit by a cosmic ray and it had knocked out the ultra-stable oscillator. But we didn't know that for several hours. All we knew was the spacecraft was not talking to us and that was terrifying. And it was only T-13, so it was very early in the mission and it was just kind of crazy to be sort of that paralyzed with, oh my gosh, since I had worked on all the Titan stuff, what did I do? Is there something I did that I didn't check? But then in a couple of hours, the spacecraft did start talking to us and we learned that it was the ultra-stable oscillator, which was something that was easily understood and easily powered on. And then we were able to execute that recovery process and we got back 87% of that data. So that was a moment that was quite memorable because moments of fear are burned into your psyche. And then a moment of personal sort of work related that is extremely memorable is I've been working with the Titan group for many years. And ultimately I got put in charge of the Titan group and there was a big task in front of us and it was several months of some of the most intense work of my life. And I remember the six, seven hour telecon that where all the big decisions were made. And I just remember like everybody came to that meeting so prepared, everybody had their A game and everybody was great. And it was just to lead a team of really, really smart people who worked really hard and they're doing their best at that moment was a pleasure. And I will never forget that meeting, it was fantastic. Thank you. So we've had a few people had a chance to get some questions and William asks, were with the images, were you able to resolve individual ring particles? So the closest we would have come to that William is the sort of the propellers. We don't know if the propellers are an individual ring particle or if they are conglomerate, but that's about as small as we've gotten. So really the answer is no, but it's possible that the propellers are individual ring particles and therefore the answer to that. You know what, actually even then the answer is most likely no, because what we see is we see the effect of the propeller. We don't quite see the propeller itself, the thing that's causing the trouble. So really the answer is no, what we see are collections of particles. Great, thank you. So Christine asks something a little bit more about Saturn itself. Can you speak a bit more on the data regarding the internal structure of Saturn, particularly the symmetry or lack of symmetry? So Saturn is quite oblative. You can even see that in a telescope with it's one of the most sort of obviously oblate bodies. The internal structure of Saturn is continues to be a mystery. Every model that we have has been run up against the data and failed. So the thing that I could tell you is we don't understand the internal structure of Saturn, but now that we have this data set and it is a fantastic data set, the signal to noise on this data set is a thousand times better than anything we've collected. I'm confident that the radio science team and Luciano Yes is sort of the key scientist who's working on that. At some point there will be a press release with what is the internal structure of Saturn. But right now what I could tell you is it is very mysterious. It is very tricky. It is hard to understand. And how great is that? That we did all this really hard stuff and we've given data to these scientists and they are all scratching their heads. Well, as a geologist for here on Earth, I have to say that we don't even really have a particularly good understanding of our own planets interior, so. That true. Well, let's ask a question and I'm not quite sure what I'll let you see if you can decide for this. What was the last date the Cassini spacecraft was sending out? Okay, so the last, so yes, so the very last moment that Cassini was sending data back to the Earth was Friday, September 15th. In Pacific time it happened in the morning and it happened at, was it 4.55 or 5.55? Let me just think for a second. So it was 4.55, 06 was the predicted time when the atmosphere of Saturn would cause the spacecraft to tumble and we would lose signal. We actually got 22 seconds more than that. So it was 4.55, 39. Okay and Josh actually asked that question to what time did the last signal arrive on Earth and he mentioned about how, you know, for the team, you know, must have been kind of a poignant moment or perhaps even bittersweet. Yes, quite, it was, the team was collected. Cassini actually gave us a gift, most spacecraft end in a, because of an anomaly, right? You lose the spacecraft that's unexpected, you're searching for it, or there was a known problem that finally took you out. Cassini was operating perfectly, it was operating perfectly to the last second. We knew literally down to the minute when she was going to die. And so we were able to gather. We had the team of engineers that have kept her healthy all these years in the MSA. We had all the scientists over at Caltech, you know, literally a cast of thousands. We were all together, which was a wonderful gift. It was a wonderful gift that Cassini was able to give us. Okay, and Melissa asked her follow-up, which relates to that, or what was the data that it sent at the moment it lost signal? So remember there's two things. One thing is the telemetry stream. And at that time we had eight instruments on, but the only instrument that mattered was the ion and neutral mass spectrometer, because it was telling you something about Saturn's compositional, the composition of Saturn's atmosphere. And every second of data mattered. And in fact, the very last packet of data that we got from the spacecraft was the ion and neutral mass spectrometer. A couple of days ago, people thought it was the magnetometer, but it was actually ionomess. And, but as soon as you lose telemetry, remember you still have the large radio science signal. So there's no telemetry on that, but the S-band signal was the last bit of information or communication that we had from the spacecraft. The radio science team was of course doing an occultation as they sank into Saturn. There was atmosphere above them. But that S-band signal was the very last thing that we saw. Okay. Darren has a question, probably goes back to perhaps what we were talking about about the resolution of individual particles. What is or was the resolution of the camera? And I'm guessing that we're meaning the visible light camera. Well, so the resolution of what you're looking at depends on how far away you are. Maybe the question he's asking is how big was the camera? The camera was a one megapixel camera. I know that doesn't seem very big in today's standards, but remember this is a one megapixel camera that was built, excuse me, it was built in 19, like in the early, the mid 1990s. And it was launched into outer space and it operated in the freezing cold temperatures out at Saturn. So, you know, not your average one megapixel camera, but it's a one megapixel camera. Okay. And it's a, just give me a second. It's 1024 by 1024. Okay. So our iPhones are probably better cameras. Oh, absolutely. But your iPhone wouldn't operate in the coldest space. My iPhone doesn't even operate in Minnesota. I've gone to Minnesota, my iPhone is dying. We have a couple of related questions here and let me see if I can, you know, try to kind of combine these. Let's see, where did the other one go? Okay. So Dan asks, and I'm going to kind of throw both of these out at the same time. Dan asked, can you talk about how large the risks were to Cassini if it was set through a thicker part of the rig? Well, actually it was a double one. So let's do that one, and then I'll come back to the other question, which is okay. So it was a, how large the risks were to Cassini? Oh, okay. So the risks were a couple. The first one was the dust, the risk from dust particles, which turned out to be very benign. The second one was the risk from Saturn's atmosphere. The atmospheric experts told us they only knew things to within a factor of three and they were dead right about that. We came in at 150, 200 and 250 times the predicted atmosphere, but we were ready for that. So we didn't tumble until we expected to. And then there's always just the risk of something unexpected happening, but those were the two big risks, dust and atmosphere at the end of the mission. So kind of, and then there's another one, and now that I read them, I realize they're a little bit different. And so Dan also asked there, was there a contamination risk if Cassini was destroyed there within the ring site, I'm guessing? So there was, we absolutely didn't want Cassini to go into either Enceladus or Titan, but slamming it into Saturn at 70,000 miles an hour is just fine, because in about one minute, you lose a lock with the spacecraft and the spacecraft tumbles. In the next minute, she's ripped apart and melted. And so it's literally many, many times hotter than the surface of the sun and no microbe could survive. So she decontaminated as she burned up in Saturn's atmosphere. Okay. Edward asked the question, and so the destruction of Cassini was to prevent the possibility of contaminating or landing on Titan, crashing on Titan. Yes, or Enceladus. To Titan, sort of, not a danger to contaminating that world. So the Huygens probe, okay, so you have to have sort of, first of all, when you build a spacecraft, you have levels of cleaning that you have to do. If you're gonna be an orbiter like Cassini, you have one level. If you're gonna be a lander like Huygens, you have another level. So as they built Cassini, they had to, or sorry, as they built Huygens, they had to clean it much better than they did Cassini. But then also recall that Huygens, when it entered Titan's atmosphere behind a heat shield, also got very, very, very hot. And so whatever was left, whatever bio burden was left, was burned off in the entry phase. The Titan Huygens lander was still hot when it landed on the surface. You can actually see once it landed, if you look at that little movie that they put up, you could see steam, methane steam coming up all around it as it melts off all the methane around it in the permafrost. So it was one of the considerations also because Cassini had a nuclear, basically a small plutonium reactor providing heat. And was that a concern about contaminating them with the plutonium? So not really, when we went to, and just, we don't have a plutonium reactor, just make sure that what we have is, we have plutonium in like little ceramic dishes. Because plutonium decays with a radioactive half-life, those dishes are very hot. And you put them in a tin can, a titanium canister, and it gets very hot, like 700 degrees hot. And then you slap thermal couples all over it and you pull the heat off as electrical energy. So the plutonium was not really an issue once we had decided to crash into Saturn. The plutonium canister around the RTG was probably something that lasted the longest. Titanium would have been most resistant to the heat. And so it's probably the piece of the spacecraft that lasted the longest, perhaps an additional 10 or 15, 20 seconds, maybe an additional minute before it was vaporized in Saturn. Okay. So we've got a couple of other ones a little bit different here. So William asks, during the formation of our solar system, did Saturn prevent Jupiter from migrating into the inner solar system? A little bit of orbit dynamics. Yeah, I have not heard that. So I think my answer to that question is, I don't know. I've not heard that theory. And I'm not familiar with that either. So, but it would be, it would be interesting to find out. That sounds like an interesting guess for you. Certainly the big planets have had a lot of gravitational influence on the rest of the solar systems. Yes. Christine asks, can you remind us of the primary theory about the polar hexagon? So the polar hexagon is a jet stream. It is a, so a jet stream, just like the jet stream here on the earth is a place in the atmosphere where you have high velocities. On the earth, the jet stream is, you know, gets bummed around by land and mountains and war motion and cold ocean. On Saturn, there's none of that. So it can stay in one place. The fact that it is a six-sided hexagon versus say an octagon is telling us something about Saturn that we don't understand yet, but we do understand that it has set up a standing wave. That's a nice stable feature, but we don't know why it's six-sided. But it's basically a jet stream. Okay, so we're gonna call one more question here. And this is actually from our colleague, David Prosper, who's currently at the Oki-Tex star party. Yes. And he said that he's sharing this with some of the people there apparently. They've got a fairly good signal. Yay! Really good buddy. And so he wanted to know, I mean, he thinks that maybe we covered this. How long Cassini was able to transmit once it did enter the atmosphere and how long it took after that signal before it was crushed or vaporized? So about a minute for each of those from the time that it was touched the top of the atmosphere. Remember, it's going 77,000 miles an hour. It was about a minute until we lost attitude control and we started to tumble. And then it was about another minute until the spacecraft was gone. Okay. Well, that's great. Well, thank you so much, Trina. You're welcome. This is absolutely wonderful. We had some great questions for everyone. And so it's an amazing mission. Yes, it's truly been. I've been on it for 21 years. It's been absolutely one of the highlights of my career. And I worked on Voyager at the Neptune Encounter, which is also a highlight. But Cassini has been a wonderful mission to be on. And it was a fantastically well executed. There's no question looking back on it that it was one of the most well-built spacecraft of all time. The data is clear on that. It was well operated by the spacecraft team for 20 years, carefully watching consumables and the things that were starting to fail on the spacecraft. And of course, the scientists continued to put interesting challenges in front of the spacecraft for 13 years at Saturn. And she did not disappoint. She did absolutely everything we ever asked her to do. And it was a pure pleasure to work on her. Well, thank you very much for your part and for bringing the story to this crew and to the other people that you've had the opportunity to interact with. So thank you so much. You're welcome.