Planetary Radio: Space Exploration, Astronomy and Science - Celebrating Cassini…Live!

Episode Date: September 27, 2017

More than 1,100 fans of the just-completed 20-year mission to Saturn joined us for a live tribute.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Celebrating Cassini one last time, this week on Planetary Radio. Welcome, I'm Matt Kaplan of the Planetary Society with more of the human adventure across our solar system and beyond. Nothing could top last week's coverage of the Cassini mission's grand finale, but I think we come close with this week's bonus-length show. I've included nearly all of our September 18th live tribute to the mission, featuring three of its leaders, along with our own Emily Lakdawalla. The Planetary Society and I are so grateful to our partners at KPCC Southern California Public Radio. It was SCPR's wonderful in-person crew that got us Caltech's huge Beckman Auditorium and took care of all the logistics. As you'll hear, I was joined on stage by KPCC science reporter Jacob Margolis. He and I started the show by asking the more than 1,100 people in

the packed auditorium to welcome our guests. Please welcome to the stage Cassini project scientist Linda Spilker, Cassini program manager Earl Mays, and Cassini spacecraft operations manager Julie Webster. There is one more person joining us, my Planetary Society colleague, Senior Editor Emily Lakdawalla. She's here in part to represent the scores of citizen scientists who have contributed to this mission. Emily Lakdawalla.

Thank you. scores of citizen scientists who have contributed to this mission, Emily Lakdawalla. So, welcome everyone, and congratulations. I was here Friday morning before 5 a.m., about 4 a.m., for that glorious, bittersweet finish, then ran over to JPL to be with, well, Emily and Jacob were there for the press conference. It was one of the greatest mornings of, I have to say, of my life. We have so much to talk about in limited time, but let's begin with this. For the benefit of the one or two people in this very sophisticated audience who don't remember or know why, why did we crash Cassini? Earl? Well, it's been the plan for seven years. And really, the reason was to use every possible piece of that spacecraft in the most optimal scientific way possible. We couldn't leave Cassini floating around derelict around

Saturn. It was, you know, because of the potential prebiotic nature of both Titan and Enceladus, particularly Enceladus, we couldn't contaminate it. So we had to, you know, put the spacecraft away. The idea was to use all the fuel and go out in a blaze of glory, getting Saturn science for the very last second. That's exactly what happened, right? That's correct. You were getting data right to the very end.

Right to the very end. All of you, all three of you, have been with this mission for so many years. Linda, for you, what, almost 30 years? Almost 30 years, almost a whole Saturn year. You've got to ask, how does it feel to be really at the end of an era? Julie? You know, it's amazing, but it's exactly what Earl said. You know, we did it. We designed it. We knew that this day would come nine years ago. It's everything that we expected

it to be, and it was time. We were starting to worry about things going wrong. You were all together, most of you were together, for such a long time. Did it start to feel like a family? Oh, absolutely. I think we got to know each other really well. In some cases, our kids grew up together. We'd take vacations together, go out to dinner, and really got to know each other as people and not just professionals. Yeah, couldn't agree more. We would finish each other's sentences, take care of dog sit for each other. It was very, very much a family. And the entire set of skills and personalities

that you expect in a large extended family. Not like we always got along all the time, but that's what families do. I mean, there were a couple of references at the press conference to that old, old scientists versus engineers discussion, right, Julie? That's why Earl's in the middle. That's why I'm in the middle. That's why you said, you know, it's like my mother separated my sisters in church even when we were adults.

Well, we did. But Linda's going to give you my final line to all the scientists was that we were there for the science. Absolutely. When Julie said that, it just melted my heart. It was great. Yeah. And she got 23 times past Enceladus. So we worked our way in. We started way far on thrusters and worked our way in slowly but surely and just knew that there wasn't anything. So we didn't take any chances with Cassini. But we did. You pushed the envelope once or twice.

Absolutely, or half a dozen, a dozen times. That tension between engineering and science is what really makes you get the absolute most out of the mission when everyone's asking for a little bit more than they probably can get someone's saying well you can't quite get as much as you're asking for but I'll give you a little bit more than I said

that balance is what I think Cassini will take as a takeaway as one of the big successes is to find the right sweet spot between science and engineering is what I think Cassini will take as a takeaway as one of the big successes, is to find the right sweet spot between science and engineering. Absolutely. Absolutely true. We know data came right to the end. Images did not. We have, I think, the very last image captured by the spacecraft,

and you've got it in front of you on that monitor at the lip of the stage there. Linda, do you recognize it? What are we looking at? We're looking at Saturn and basically that dark shadowed line is probably just above the equator and it's actually illuminated in ring shine. And in that picture is the place that Cassini finally plunged. And so it was very bittersweet to capture that image and know that somewhere in there, there's a little piece of Cassini. Is this also a scientifically significant image? Yes, you can look and study the clouds right to the very end. We've been looking at seasonal change on Saturn for almost two Saturn seasons, so scientifically interesting as well.

We have one of your favorite images from the mission that we're going to pop up now. It's also one of my favorites. I had this on the back of my business card for years, but the resolution wasn't high enough to really see what's going on here. Talk about it. This is a wonderful image. Basically, you're looking at the sun in eclipse, in this case by Saturn. And you can see all of the rings.

The sunlight is shining through the tiniest particles, much like if you have a dusty windshield and it's hard to see when you drive into the sun. I like it because you can see all of Saturn's rings in one image. And as Emily pointed out, if you look at that bright ring around Saturn, it's the sunlight being refracted through the atmosphere. And you're looking at every sunrise and every sunset at the same time. And that's just amazing. And you'll notice that the night side of Saturn is illuminated. That light from the rings is actually falling on the night side and is brightening it.

And if you look very carefully, there are three other planets. So this is the Saturn view of the Earth and Moon system, and also Venus and Mars. What was really special about this opportunity is that we reached out to the public and said, okay, there'll be a 20-minute window. This was in July, I think, 2013. A 20-minute window, go out, wave at Saturn. And we have pictures. Here you go. Here is everybody at JPL. I love the hula hoop crowd for the ring tribute, of course. It was so wonderful. And then we asked people, send us your selfies.

Because, you know, you're going to be kind of small. The earth is only like maybe a pixel or two across. So we took all of these selfies and put them together and recreated that mosaic that you just saw and so we have I think with the next image with those selfies oh I don't think we have that

we recreated that beautiful image and it was so wonderful it was one of our most popular images because people were going through trying to find themselves in that particular image and I did the same thing to find themselves in that particular image. And I did the same thing. Where am I? Where am I in that picture?

Emily? I think somebody did the math to calculate the likelihood that a photon from a waving person's hand would have appeared in the image that Cassini took. And it was something like if you stood out there for the whole 20 minutes, it's like there was a one in five chance that a photon from your hand would have actually reached Saturn for that picture. Not bad. I'll take that. Okay. I was waving really hard, so maybe I got two photons. We have so much more to cover tonight. And it's going to be an interesting evening as it is punctuated by these, I think you'll agree, marvelous presentations

that Jacob has for us. It has obviously been a long, long journey to this celebration tonight. Jacob, give us some context. All right. Today, we're going to hear all about the triumphs, the discoveries, and enduring mysteries that came up during Cassini's mission to Saturn. But before we go over what we've learned, let's go back to humanity's first encounter with the planet.

Before the crash, before Cassini, before NASA, even before the United States, there was a guy named Galileo. You've heard of him. He was the first to observe Saturn through a telescope in 1610. But Galileo didn't see a ring. He actually described the planet as having handles. Of course, that's because his telescope was maybe not as advanced as ours today. planet as having handles. Of course, that's because his telescope was maybe not as advanced as ours today. It wasn't until later that century that Dutch astronomer Christian Huygens proposed a

crazy idea that the planet was actually surrounded by a giant ring. But it wasn't until the 1700s that an Italian astronomer, and you might recognize his name, Giovanni Cassini, figured out that what they were looking at wasn't one big ring, but multiple rings. Now, let's take a big jump. We're going to go to the 1980s, because that's when one of our biggest sets of discoveries about Saturn came from JPL. These people here in Mission Control were responsible for guiding NASA's 1,800-pound unmanned Voyager 1 spacecraft some billion miles through space. Driven by our curiosity of the cosmos, we launched space probes deep into the solar system. They, of course, were Voyager 1 and Voyager 2. And after quite a long journey, they arrived at Saturn. Because of human ingenuity, we saw our clearest photos to date of the gas giant, its many moons, and its

thousands of glorious rings, largely made up of little chunks of ice. Truly, the veil had been lifted in unprecedented detail of the outer reaches of our solar system. What was the reaction from the science community and the Voyager mission team when those close-ups from Voyager of Saturn started to flood in? Linda, I know you were, were you on Cassini by that time? Or no, you must have still been on Voyager. I was on Voyager at that point in time. And for me, as a ring scientist, I remember that there was some thinking that the rings would be these bland sheets of material. And as we got closer and closer, this incredible detail looking like the grooves on a phonograph record, and it was just astonishing to see that

detail. And these little moons that had been points of light, bit by bit, we started to reveal and better understand what they look like. So it was amazing to be on Voyager and be one of those early explorers. Earl, was the inspiration provided by Voyager, was that partly a driving force of wanting to get back to Saturn with Cassini? Oh, absolutely. I think that the Voyager, as has Cassini, raised as many questions as discoveries. And, of course, we had to go back. And I think it was also part of the campaign NASA had put together of these reconnaissance missions

following on the heels of the flyby missions. Galileo did that at Jupiter, and Cassini was the logical next. Saturn was the next logical target. We still have a couple of large bodies to go yet, but there was no doubt that Voyager is showing us these planets and mysteries that we simply have to go back and explore further. I think in particular was the moon Titan. One of Voyager 1's key goals was to fly close to Titan

and see what its surface looked like. And instead, all that Voyager 1 saw was this ball of photochemical haze, smog. And so immediately after the Voyager flybys, scientists started to get together and said, let's go back. Titan is still a key objective. Let's go back with a probe, with radar to pierce through the haze. Let's go back and study Titan. Now, I was five years old when Voyager flew past Saturn for the first time. So I don't remember the actual flyby happening, but I do remember a time-life book I had on our

solar system. And I remember reading and seeing the names of all these wonderful different looking moons. There was Enceladus with funky looking craters and Dione with wispy terrain. And Rhea and all these different icy moons, all these names that were not the names of the planets that I was familiar with. And I've been fascinated with those ever since I was little. Julie, did the success of Voyager support help out with the design and building of Cassini? I mean, were you able to take lessons from its success? Oh, absolutely. We took from the Voyager more some of the failures of the, and the Galileos and the Magellans and the thermal design and JPL up until Cassini had a thing about this, the people did the same job kind of over and over.

So you had an amazing amount of experience on the floor building and testing Galileo. I just want to add one picture about the backlit picture, one comment. As an engineer, what I see is the multiple images and how stable that spacecraft is. There must be some engineers in the audience. Can we get an idea right now? If you're a Cassini team member, give a shout.

Or anybody from JPL. Well, congratulations to you, too. Emily, briefly. Speaking of Voyager inspiration and Voyager leading to Cassini, I know that there are actually spare parts from Voyager that were included in Cassini. Yeah. Julie? It's actually not spare parts, but the same design.

We had the same basic thrusters as Voyager did. And our main engine, the thing that was the big engine, was thrusters on Apollo. So we had a lot. We had a computer that was an upgraded version of Magellan and Galileo. But the thermal design, I think, has always been one of my favorites. It was such an incredible, you know, the spacecraft ran at room temperature, basically from Venus to Saturn. And Cassini's camera optics actually had some Voyager parts included in it. Right.

And some of the other instruments are basically upgrades to the Voyager instruments. The composite infrared spectrometer is based on a Voyager instrument, just better detectors. So if it ain't broke. That's right. That's right. Clearly, the pictures and other data from Voyager instrument, just better detectors. So if it ain't broke. That's right. Clearly the pictures and other data from Voyager whetted everyone's appetite because scientists and engineers at NASA spent the next decade figuring out how to get back to Saturn.

It was the 1980s, and JPL scientists, like Linda Spilker. Hi, Linda Spilker. How's it going? We're excited to get back to Saturn. But space is hard. The vision wasn't easy to execute. It was going to cost a lot of money. There were arguments over what instruments should go on the spacecraft and what route they should take to get there.

Twice, Congress threatened to cut funding. On top of all that, there was this public uproar over the nuclear fuel source that if it exploded, people were really, really worried that it would contaminate Cape Canaveral. But luckily, in 1997, it happened. And liftoff of the Cassini spacecraft on a billion-mile trek to Saturn. Cassini launched with far better cameras, or with some of the parts from Voyager, with instruments that could help her measure chemical compositions,

atmospheres, molecules floating through space. And traveling at tens of thousands of miles per hour, Cassini departed through the Earth's atmosphere, beyond our Moon, Mars, Jupiter. And after seven years, in 2004, she arrived at Saturn. There was a lot about the gas giant that we still didn't know. For instance, we didn't and don't know the exact length of a Saturn day. We needed to test our understanding of what Saturn was made of, and we weren't sure the origin or age of the planet's rings. Also perplexing were the massive storms that engulf large swaths of the planet for months at a time. Oh, and I mean, let's talk about this giant stormy hexagon on the North

Pole, because I'm not sure how weather can have six-sided geometry. But, you know, with the hurricane eye at the center, which is really nuts, the more data scientists sifted through and the more Cassini circled the planet, even more questions everyone had. And there was a long way to go to better understand the basics of Saturn, even though we've been looking at it for more than everyone had. And there was a long way to go to better understand the basics of Saturn, even though we've been looking at it for more than 400 years. So we didn't have to wait for orbital insertion, for science from Cassini. How early in the mission did useful data start to arrive back here on Earth? Linda?

I think probably maybe six months, maybe a bit more, we started taking pictures of Saturn. Six months out from Saturn? From Saturn orbit insertion. And we saw this little tiny planet, and it slowly grew bigger and bigger, and saw more detail in the rings, and we thought we're going to take a whole lot of science going in, just in case something happens at Saturn orbit insertion. Talking about engineering and science often in conflict,

there was a very wonderful symbiosis between the two. We had to test the motor before we did the Saturn orbit insertion burn. So the best way to do that was to make sure that we had something on the order of 50 or so meters per second to test out the entire propulsion system before we went into orbit. Well, it turns out if you put that 50 meters in the right place, there's this captured Kuiper belt object out there waiting for you called Phoebe. So we actually had our first close flyby

was before Saturn orbit insertion. We did a test burn afterwards to go back in towards, and that was Phoebe. Remember that? It was just a beautiful object. And again, for the sake of engineering, we did science at Jupiter. We had this wonderful... And Venus, and Venus. But always for engineering. This was not the science objectives. We launched Cassini without all the capabilities to do operations at Saturn. And Julie's crew spent the entire...

Our crew, actually, at the time, spent those seven years developing the capabilities, and we tested them all out at Jupiter. And Galileo was still there. So we had an inside-outside campaign at Jupiter with Cassini surfing in and out of the magnetic field while Galileo was propelling around inside. It's beautiful. We have an iconic image of Jupiter that we're still very proud of.

Saturn science was turned on six months early, around inside. It's beautiful. We have an iconic image of Jupiter that we're still very proud of. Saturn science was turned on six months early, but you know, the camel snuck its nose under the tent a lot sooner. Well, as soon as we launched, you know, Earl and I were planning to fly a rock, which has always been the joke. And as soon as we knew that we had a good spacecraft and there were no issues, the sciences started clamoring. But remember the first two, three years, we had to go to Venus, back to Venus, and then by Earth. The high-gain antenna, which was our main communications, was used as a sunshield. So we had very, very low bit rates. And we didn't turn the high-gain back to use it as a communication device until 2000.

Did you have to use, because of that huge high gain antenna, did you, using it as a heat shield, did you have to, as you navigated, take that into account with the solar wind and just the light of the sun? It all had to be considered, right? Absolutely. Yeah. And the heat from the RTGs and the solar pressure and the pressure. The mag boom wasn't out until after we went past Earth. But, yeah, all of that had to be taken into account. And the navigators were saying, you move Cassini, you move Cassini. It was like. I didn't.

But, yeah, all of that. And it was well modeled. It was an amazing modeling job. Got some amazing navigators that you work with there at JPL. Absolutely bright people. So as we're approaching Saturn, how did it feel to see that planet growing in the sky? Linda? It was tremendous for me to see it, having worked on Voyager in the 1980s and then all the way to 2004 to be back and looking at Saturn and the rings

and just the promise of what was there. We just had a four-year prime mission, but we had packed it full of incredible science observations. I remember the tension in the room on that July day, 2004, as we were waiting with you to see if things were going to happen right. Julie, you're nodding emphatically. Tell us, what were we waiting for? Well, we weren't going to get any signal back until after the engine burn was done. And if you remember, in 98, 99, NASA had some losses. So they invoked this rule on us that

said, thou shalt not do a critical event without telemetry. We were not pointed at Earth to get down telemetry. So we had to switch to our low-gain antenna, which was about 80 degrees off Earth point, Earl? I think it was 60. 60 degrees off. And so the radio science team came in and said, we can pick this signal up 10 dB above the noise floor, and we'll find it for you, and we'll track the Doppler and be able to say that you got into orbit. So the Doppler, which indicated the change in velocity when the engine came on, right?

We changed the velocity by 630, roughly 630 meters per second. That's a lot. It was the biggest. It was a 96-minute burn. So it was a big burn. If those guys hadn't figured that out, we would have been out about another 120 kilos of fuel. Yeah, NASA came back and asked us to point the antenna at Earth,

even though that made the burn not in the right direction. I went back to NASA headquarters with Bob and argued that we could distinguish well enough without any telemetry that all we needed was the carrier signal, and the radio science did it for us. Wow. Yeah, I remember watching that plot, and there was a period of time we were behind the planet. Behind the rings. Oh, behind the rings, and watching for it to pop out and see were we on that plot. Yep.

And sure enough, we get the signal, and there it was, right on the money. Cassini settles into its new home, orbiting the planet. We're going to get to the moons and other stuff pretty soon. Were there surprises? Were there revelations about Saturn, and really the system, right from the start, like that hexagonal storm that Jacob is so excited about. I think about the ring images that came right at orbit insertion. It was the closest that Cassini got to the rings for a very long time.

And the incredible regularity of the features in the rings. But they also weren't exactly spaced. They were regular and diminishing in size, these waves. It was just incredible to look at. Yeah, very beautiful. And also, the first time we saw propellers, these little objects in the rings that would try and open a gap and would have these two arms that look like an airplane propeller. First time we saw those. I try to imagine what the rings would look like if you were actually in them. And it's difficult because some parts of the ring, like the A ring, is partially transparent. So maybe the particles aren't all right next to

each other. But the B ring is quite opaque, which means that the particles have to be close enough to each other to overlap. I mean, I wonder as an astronaut if you could just leap from particle to particle, just kind of jumping around inside the B rings or above them. It would be really cool. Right, especially if they're these iceberg-sized objects. It might take you a long time to land on another one, but it would work. So the rings, obviously, huge diameter, but one of the most amazing facts about the whole Saturnian system, the thickness of the ring system, Linda?

It's only about 10 meters thick. So they're just incredibly thin for their wide size. You could fit Saturn plus the rings in between the Earth and the Moon. That's how big that system is. Very briefly, what does it mean that you process this image? Well, Cassini, like most spacecraft imagers, has a black and white camera that's designed so that each of the little pixels on its detector is basically a photon counter. And it's counting up scientific data, how many photons in a certain wavelength range struck that little spot in the detector. If you want color information, you throw a filter in front of it. So you limit the amount of the different color photons that can strike the detector.

To make a color image, you throw first a red filter and then a green filter and then a blue filter in front of your camera, take three pictures and stack them on each other and you can make color. The catch with Cassini is that Cassini is moving, the moons are moving, the ring particles are moving, and they're all moving in different directions at different rates. And so it's actually not all that easy sometimes to combine these images. So it can take a little finesse. Plus, there's a small problem of cosmic ray particles flying around all over the place. And they tend to do nasty things with the CCD detector. They make these bright streaks. So you have to do a little painting, a little cutting and pasting. This is art as much as it

is science. But it's great fun because Saturn makes the greatest art to work with. So Earl, just even getting the original image, it's so much more difficult and complex than just holding up your smartphone. Well, that's exactly right. And the spacecraft essentially has to propagate the motion of that little satellite through those rings, compensate for Saturn's motion, the ring's motions, and that little satellite's motion, get ring's motions, and that little satellite's motion, get those all put together and point the camera in the right place. And that's all done piece by piece. Each little piece is added on to the next piece. And it's kind of interesting because the first time we did this, we didn't do quite as good a job of tracking

Daphnis as we would have liked, but we tracked the rings perfectly. And so the rings people were ecstatic because we got the rings just nailed. And you can see this incredible structure in it with Daphnis off in the corner. And then we came back and of course got Daphnis, which blurred the rings a little bit. You can't have them both. But it's incredibly, as Emily said,

everything's moving counter to the other components and you've got to pick the one you want and concentrate on it. We're coming back to that hexagonal storm. Do we understand it now? Do we know how dynamically that thing has lasted for what? How many years, Linda? Well, we saw with Voyager in the 1980s, it's still there, still going strong. Six sides, it rotates around as a unit,

and any little clouds that get trapped on the outside, just like cars on a racetrack, they zip around faster than clouds inside or outside. It's a six-sided jet stream. The South Pole doesn't have one. Jupiter doesn't have them. It's very unique to Saturn's North Pole, and we're still puzzled about why it's there and what's keeping it there. But other planets have dipoles. So on Venus and Mars, we've seen dipoles. What do you mean? What is a dipole? So this is like has six, it's a wave number six wave that's traveling around the North Pole. And in Mars and in Venus, you see a wave number two going around the poles. And so many, we even see that on Earth from time

to time. Sometimes Earth has a dipole as well. So it's not that unusual to have a sort of a standing wave, but this hexagon is particularly pretty. The interior of the planet. I mean, we wanted to know what's going on at the core of that planet, right? Has Cassini helped us to understand the structure of Saturn? I think the grand finale orbits, those 22 orbits in between the rings and the planet, bring us closer than ever before to get detailed gravity measurements, magnetic field measurements,

and there have been surprises. For instance, the magnetic dipole and the spin axis of the planet are almost right on top of each other to 0.06 degrees. And we were looking for a wobble that would help us get the length of Saturn's day. But so far, it's just perfectly lined up.

The interior of Saturn is not what our models predicted. We're not sure what it is, but it's not what our models predicted. So we'll have some interesting information about how Saturn formed. Does it have a small core, earth-sized little core? What's going on inside of Saturn? So give us another six months or a year. We're getting closer. Earl, when that grand finale started last April, that first dive between the rings and the planet, how nervous were you? I was nervous. That was probably an 8 on a scale of 1 to 10.

We had really put everything we knew into the models. We had never seen that region between the planet and the rings, and we could only extrapolate based on the dust that we had seen. And we thought it was benign, but we really had no idea. Of course, the spacecraft, for our first plunge through, we used the shield of the high-gain antenna into the oncoming dust, just in case it was even worse than we thought. And we didn't call home for some, what, eight hours later? Twelve. Twelve hours later. So it was twelve hours of wondering. And then

what we really were waiting for was the call home, and it was either going to come home fine or not. And I was very apprehensive because we'd staked everything on this being a clear passage. In hindsight, we were as wrong as we possibly could have been. Not only was it not dusty, not too dusty, It was not dusty at all. All the dust had been eroded down to nanoparticles. So we were able at that point to completely retire any contingency plans we had about using the Hygiene Antennas as a shield. And my relief was very palpable. But Julie, you did get pinged by a few of those nanoparticles, right? No, no. Oh, you didn't? The radio and plasma wave, the one that has the three antennas,

which, you know, would go, if it felt a particle, they got nothing. Well, the particles were so tiny that when they did hit the antennas or hit the spacecraft, they weren't big enough to make an electrical signal. Right. So they were there, but benign for Cassini. But that was probably the most nervous time for Earl and I that in the last three or four years was that April event. That was the one I had to be reminded to breathe.

Except for that eight meter per second burn. We were, we've been watching the gas gauge for the last two and a half years. And we did one big burn, and we were all, we had everybody at the ready in case we ran out because we were going to have to turn around and try to finish that burn up on these little tiny thrusters. And when that finished, I was also really, really relieved.

How long is Saturn's day? Sounds like it would be an easy thing to figure out, right? Not so much, Linda? No, if you look at Saturn, you're just basically looking at clouds and gas. And so the clouds rotate at different rates. The different bands go faster or slower. What we're looking for is the internal rotation rate to pin those cloud speeds down. But we don't have it. We thought we had it with Voyager. Turns out it wasn't what we thought. We're still looking. it. We thought we had it with Voyager. Turns out it wasn't what we thought. We're still looking.

I wish we had more time just to talk about the planets, the planet and the rings. But of course, that's not the only thing the Cassini mission was about, the planet and rings. It was about Saturn's moons as well, in particular, Titan and Enceladus. When the spacecraft launched in 1997, attached to it was something called the Huygens probe. Remember, it was Christian Huygens who realized that Saturn had a ring, but he was also the first to spot the moon Titan. Titan, by the way, is the second largest moon in our solar system, 50% larger than our own, and lingering questions, as you heard from the panel, about Titan from the Voyager mission was a major reason why we sent Cassini back. The goal of the Huygens probe was actually to land it on Titan's surface to

find out what was going on there. But that's hard to do when you haven't seen the surface before. See, Titan, as we also heard about and as you can see, is covered in a hazy orange atmosphere. It's made up mostly of nitrogen and methane. So scientists didn't know if they were going to land this billion-dollar probe on a mountain in the middle of a mudflat or in an ocean, and they didn't know if it was going to sink, crash, or land safely. So for a bit, the team watched Titan from above, and in the winter of 2004, they went for it. Cassini and Huygens, who had spent seven long years together adventuring through space on a grand quest, had to say goodbye. They gave each other one last look, one last long embrace, and detached. Huygens' descent to Saturn,

to Titan, excuse me, had begun. Into the orange haze, taking pictures, analyzing the atmosphere in the surface below, reaching out to Xenia with crucial pieces of data she was gathering on her way down. And what she saw was magnificent, a landscape nearly a billion miles away that looked a lot like Earth. It had rivers and lakes and mountains, but this is space. Things are crazy. Those rivers were made of methane and ethane, and the mountains were made of ice. Huygens' parachute deployed, and she drifted down, landing safely on a mudflat. All told, Huygens transmitted data back to Cassini for about four hours or so. After that, Cassini's friend was gone forever, stranded on Titan.

But we learned a lot about one of the most mysterious moons in our solar system, including the fact that it might contain precursors to life. So with any luck, maybe someday there'll be a little fence around Huygens sitting on the surface. It'll be a photo stop on the Titan tour. Earl and Julie, engineers, how impressed are you that the European Space Agency was able to build a probe, a craft that could do this? Are you going to tell the story or am I? Go for it.

Oh, goody. They built a great spacecraft. They built a great probe, but they forgot to put Doppler correction in at the bit level. Cassini and our navigation team took the first two orbits of Saturn, made it into three orbits. So Titan 1 and 2 became Titan ABC. So we changed the way we flew by Titan so that we could get the signal back clearly. And we started looking at that in 2000, and it took us two years to actually figure it out,

figure out the trajectory, change it, and then do all of the course corrections along the way. So I wasn't seeing the pictures. I was seeing the downstairs in a basement of an ITL testing sequences. So was there ever a chance that you were not going to get the data back from Huygens? Absolutely. There's a great story of human persistence here. We launched thinking that we'd done all the appropriate testing on the ground and that Huygens didn't need to be tested again.

But there was an engineer on the European side that absolutely insisted against great resistance from his management, both personal and professional, that we would actually test it in flight. And so he brought the equipment to the Goldstone tracking station. We made Goldstone look like a descending probe, and we tracked it with Cassini, which is exactly how the data was supposed to do. Cassini tracked and recorded the data from the probe.

It didn't go directly to the Earth. We looked at the data, and they said, we had a great test. We'll get back to you. And it was several months later, it was, well, the test wasn't quite so great. We've got a serious problem. And we quickly formed a nice team. And got the problem solved. It's a long story and rather subtle. It's not an easy thing to catch. But it was the

persistence of this engineer that just absolutely said, we must do this. Never, it's again, just don't give up and test, test, test. And otherwise we would have been sitting there on January of 2005 with nothing. He sat in the base of one of the Goldstone antennas and hooked up his computer. So it was one Goldstone engineer in Boris hooked it up and sent bits. His management truly insisted that they didn't need to do it. And when he did, it saved the mission. I was told that it was similar, and this might be breaking it too simple, that it was similar to someone tuning into like 89.9 instead of 89.3.

Like something, is that a little too simple? Just to pick some frequencies randomly. That's what I heard from a scientist. A real life scientist. Huge mistake, obviously. I don't know. But it really is a little it's the right idea.

There's so many different layers of Doppler compensation and locking loops inside these receivers. You're talking about minuscule signals that have to be very precisely timed in order to get above threshold. And it just was a very subtle error. And unfortunately, what happened was that the designers, a lot of times you put these in firmware

so you can change the settings. This was hardwired in. And so the only thing we could do was change the trajectory of Cassini. Huygens had to do exactly what it had to do, but we could move Cassini further away. And fortunately, there was enough margin in the link connection that we could stay some 60,000 kilometers away and still track the probe going in. And not only that, but the navigators managed to do it, as you said, by replacing two orbits with three. And in so doing, that meant that all the science planners didn't have to change any of their science plans for the remaining however many dozens of orbits they had already begun doing their science plans for. So that really saved the science teams. That's right.

Oh, yeah. And it was fair to say that Huygens, as we've probably heard in the past, has come to our rescue back in 94. We were slated to be X'd out of the budget by Congress. And I've got the letters from the community in Europe that are passion-pleased to not do that. And indeed, that was exactly what happened. So we were very happy to reciprocate. Has it paid off? Absolutely. No doubt. This is exactly where I was hoping we would go because this was an international mission. ESA came up with

Huygens. But the Italian Space Agency, I don't think enough people know about the role that they played. Well, that's right. They built the antenna. And the antenna, the high gain, is a unique... It's not just any parabolic antenna. It's a five-frequency antenna. It's a very specialized design and antenna. And there's a lot of radio. There's a lot of diplexers and combinations inside

to compensate for keeping those frequencies separate. Now I have to laugh because you take that antenna, every time you go through a dust hazard, you point the antenna right at the dust hazard. You're right. It's sturdy. It's still the best. They also built the image, the visible part of our VIMS instrument, our visible infrared mapping spectrometer,

as well as significant components of the radio and radar systems. So their contributions were significant throughout the mission. And Galileo Aficion built the Star Tracker. Right, we paid for those. Those were not Aussie contributions. We actually paid for them. But yeah, their Italian components, other than their contributions that were part of just the international components of the spacecraft. How did having both of these result in better science? Well, Huygens provided ground truth.

We knew what the landscape was, the composition of the gases coming out of the surface. So we had one point on the surface we knew very well. And then with the rest of the mission, we could use the radar, look in the near infrared and map the rest of Titan and put it in context with this one point from Huygens. So that was very valuable. And also as we went down through the atmosphere, ground truth also for the composition of the atmosphere, the pressure and all of the things that Huygens could do uniquely on the surface. Yeah, the atmospheric density, which the engineers and the scientists came up with different densities at Titan because we used the thrusters and the scientists were using INMS, the mass spectrometer, that got the last data at Saturn. And we had a huge factor difference, and Huygens provided the ground truth on that one, too. That, you know, if the map in your eyes aren't right, you know, the map's wrong.

Cassini's remote sensing ability notwithstanding, Titan's atmosphere is still really good at cloaking the planet and making it difficult to understand what's going on on the surface. I'm still dubious, for instance, about claims of active volcanism on Titan that are made from the orbiting observations. But when Huygens landed and saw rounded cobbles on the surface, there is only really one way to take some chunky broken thing and round it, and that's to roll it in a fluid. And so that, to me, as a geologist, is incontrovertible proof that there really is liquid rolling across the surface

to make those channels. And so there's really nothing you can... to replace that. Huygens was amazing at what it showed us. Right. We actually watched it rain on Titan. Parts of the surface darkened. You can imagine, like, a desert thunderstorm. And then slowly that surface dried up,

seeing lots of clouds and weather. And what was really nice in the beginning, the North Pole, there was like a lot of clouds and very thick covering. And then as the seasons changed and the sun came up, it's like those clouds kind of parted, and we've gotten really wonderful views of these large lakes and seas at the North Pole, sort of rimmed with some kind of interesting material. We've been watching to see if they would evaporate, no change in lake level,

looking for waves on their surface, evidence of wind. So the clouds did kind of part in the north, and that was really nice. Talk about that mysterious island that comes and goes. We call it the magic island. Sometimes it's there, sometimes it's not. And it turns out there are several places that have these features. We're not sure if it's maybe bubbles coming up, something just beneath the surface. We just see it in radar.

But they tend to come and go, and we keep looking and haven't exactly figured out what they might be. I like the person who told me, oh, they're cryo whales. figured out what they might be. I like the person who told me, oh, they're cryo whales. The second half of our live celebration of the Cassini mission is still ahead, and so is your chance to win great space art in this week's What's Up Space Trivia Quiz. This is Planetary Radio. Where did we come from? Are we alone in the cosmos? These are the questions at the core of our existence. And the secrets of the universe are out there, waiting to be discovered.

But to find them, we have to go into space. We have to explore. This endeavor unites us. Space exploration truly brings out the best in us, encouraging people from all walks of life to work together to achieve a common goal, to know the cosmos and our place within it. This is why the Planetary Society exists.

Our mission is to give you the power to advance space science and exploration. With your support, we sponsor innovative space technologies, inspire curious minds, and advocate for our future in space. We are the Planetary Society. Join us. Welcome back to Planetary Radio. I'm Matt Kaplan with much more of our live tribute to the Cassini mission and team.

Let's go back to the standing room-only Beckman Auditorium at Caltech. It was the evening of September 18th, barely three days after the spacecraft had plunged into Saturn's atmosphere. Delivering great science up to the second it began to tumble, and only a minute or so before it broke apart and was vaporized. Emily Lakawala, Jacob Margolis, Earl Mays, Linda Spilker, and Julie Webster were still talking with me about Saturn's tantalizing moon, Titan. I don't think there are any astrobiologists up here on the stage.

Maybe we have some in the audience. But I know astrobiologists who are actively considering how life could exist in this frigid place, beyond frigid. Obviously, it wouldn't be life as we know it. Do you find this line of research interesting? Linda, I guess you go to you again. I find it very intriguing. Could you have life that could use liquid methane in place of liquid water and have the chemistry that you need. It's cold there. It's not as efficient to use methane compared to water, but there is a possibility. There have been calculations by astrobiologists.

It would be very interesting to send a boat into one of these Titan seas and make some measurements to see just what you find there. The seas are really very deep on Titan? They're shallow. How deep are the seas on Titan? Well, we've done bathymetry and we know that some are about, there's over 100 meters on one of them that actually, so they're not just shallow ponds. They really are, I think we've likened them to the volume of the Great Lakes. Right. It's about the same depth of the Great Lakes, about the same size as the Great Lakes. Huge, tremendous volume of methane.

And this was something we didn't know we could do. We bounced the radar off the top surface of the lake, got a really strong booming signal. And actually this young person who had worked on some other data looked at it and said, look, there's a second signal. I think it's bouncing off the bottom. And sure enough, we could then map the bottom of the lake and see how deep it was and how much methane was inside. You already mentioned the speculation or the proposals that have seriously proposed a boat to go sailing on the seas of Titan.

I got a great T-shirt that says Surf Titan. But there are other proposals as well. Earl, what would you like to see go back to Titan? Well, I think the boat is clearly one, but I think the edges of those lakes is where I would want to see something going on, something that could... I have no background in astrobiology,

so I'm afraid to speculate wildly without any repudiation of my professional career. But I think that what's going to happen is going to be at the edges of those on the shores. We've watched this odd sort of, as the lakes come and recede, some coloration changes and structure changes. So I'd like to actually see something that could spend time at that fringe. And putting a plug for my robot buddies at JPL, we've got the technology. It just needs to be operating in very cold.

But that's where I'd like to go. Titan is an aeronaut's dream because it has a relatively thick atmosphere. It's about the same density as Earth, a little bit denser. But the gravity is much lower, and the atmosphere is much taller. So you could take, say, a balloon or some other kind of fairly simple gliding aircraft. And, you know, if you were human there in an appropriate spacesuit, you could take like little wing-like device and just flap around in the atmosphere. It would be wonderful. So some kind of flying thing that could go up, catch a trade wind, go down, sample the surface, rise up again, and just kind of dot all over Titan

and take pictures would be lovely. Juliet, I was just talking to somebody who was talking about a quadcopter, like a drone that so many people now own. Really? That's true. That's a mission proposal in New Frontiers to fly a quadcopter on Titan. A quadcopter on Titan. Okay.

I'll volunteer to be the one on the surface with the remote. We'll go. We'll go. Just tell me how to get there. We've gone below the surface of those seas, but even deeper down, we've learned that Titan is a world of multiple oceans, because if you go deep enough, right, there's a water ocean. Linda?

Exactly, a liquid water ocean underneath Titan's icy crust. We wonder if there might be a connection somehow to the surface. We know that methane needs to be replenished because it's broken apart in the top of the atmosphere, and over time it would disappear. If all the methane is gone, Titan's atmosphere would collapse. So something, some process has to keep releasing methane. Maybe it's with water with some ammonia like an antifreeze, and it can carry methane up. We're not sure of the process, but we know it has to get replenished. And this is a discovery by Cassini, right?

The confirmation of that water ocean below the ice? That's right, with the Cassini gravity measurements. With the radio science, yeah. And also, I think the radar tracked features on the surface, and you can see the whole crust of Titan rotating a little bit on top of its lubricated ocean water layer on the inside. It turns out that Titan isn't the only moon of Saturn, hiding a warm and inviting ocean that might be able to support life. Jacob? It's not all about Titan. There's also Enceladus.

It's a much smaller moon, right in the of Saturn's E-ring. But what you really need to know is that it's actually a perfect little snowball floating through the cosmos. Titan was weird in how Earth-like it was, but Enceladus was weirder. See, when it was initially spotted in the 1980s or so, scientists were able to figure out that it's always covered in a fresh coat of snow, like powder, stuff you could ski on at Big Bear, not during a drought year. But there is no atmosphere, there are no clouds, there's no snowstorms around the moon, yet there's always this fresh powder. So the question was why? Well, Cassini went for a trip to try to figure it out. Passing by Saturn, it eventually arrived

at Enceladus. When it got there, it spotted something unexpected and magnificent. Giant geysers of water shooting out of the snow and ice, 50 miles into space at supersonic speeds. Cassini was able to actually taste some of the mist, and it turns out that it was really salty. It was actually salt water shooting out from this moon a billion miles away. Scientists use that data and other measurements to figure out that there's likely a global ocean beneath the crust. And there's a giant heat signature on the South Pole, which is actually boiling water,

pushing it up through the ice and into space. All told, they spotted 101 geysers, and Cassini made another miraculous discovery. Because beneath all the ice, there's possibility that the snow-white moon could be harboring life. Before we go on, haven't these little multimedia segments been terrific? I want to thank Jacob for presenting these. Thank you, Matt. Okay, here's another image that Emily has provided. It is another gorgeous one of those geysers spewing out of those so-called tiger stripes. Emily, did you have to work to get these to stand out? You know, Cassini has amazing cameras, and they're much more sensitive than the cameras that you and I have.

So a lot of what you're seeing here is really very faint light. But then Enceladus is a very bright surface. Like Jacob said, it's very snowy, and so it tends to reflect light very brightly. So you have to work to kind of combine images, parts with different exposure levels in order to make the geysers pop out and see all the detail in them while also being able to see detail in the surface. Matt's giving me credit for processing these, but I have to give credit right back to the Cassini imaging team

and to the navigators and to the engineers who built such an incredibly stable spacecraft. The images are so crisp. All I see is seven target Enceladus. Say that again, Julie. All I see is seven target Enceladus, offset. But it is. It's the stability of the platform itself on the spacecraft that allows you to build these kinds of images and take them over and over.

Take long exposures. Take long exposures. Take long exposures. Pull out that subtle detail. And it was easier, right, Earl, with Voyager, because Voyager had a little movable camera platform. You had to move the whole spacecraft. Right. Well, there are two sides to all those stories.

And one, as Julie has alluded, is that when you bolt your Hasselblad onto a brick and don't move it, it is incredibly stable. We had an early experience with the spacecraft. It was so stable that we actually burned out a pixel on one instrument because it had the star right on that pixel for 20 minutes. But once we figure that out, it's just phenomenal. Now, of course, the downside to that is that when imaging wants to go to Enceladus, so does everybody else. Come back to the team's ability to collaborate and share, we got the best of both worlds.

I think what Julie's alluding to is originally before Cassini was de-scoped, we had a scan platform on one side, a turntable on the other for the fields and particles, a movable radar antenna, and it was really an incredible machine so you could do a little of everything every flyby. With the de-scopes, the scan platform disappeared, the turntable disappeared, the extra antenna disappeared, and you now had this lean, mean machine,

but a very stable platform for pointing. And you would have had only half the number of instruments because you still had the same amount of power. So I still... Yeah, I think overall, given 13 years and a chance to spend the time that you needed, then we got back the science we had lost by taking these off. We had a wonderful, very capable scan platform pointing in all directions on paper. But the reality of that system never really sunk in,

both in being operable and implementable. And I think, again, reality set in, and we got a good one. I think reality really did set in, because we would have been out of fuel a long time ago. So I really think that the body fix made it. Incredibly subtle images. When you've got a scan platform, there's always motion compensation and so many different noise factors that have to be in that we've been shed of.

And that's, I think, given us a tremendous insight. There's some observations, I won't get into them, about Enceladus's nutation that I'm not sure we would have been able to do with the SCAM platform. Right. And it took 10 years of observations to look for this slight wobble that led to the fact the ocean was global and not just at the South Pole. You mean of Enceladus. Or of Enceladus, sorry, of Enceladus. Yeah, 10 years of observations. Emily? I think it's worth, these images are so kind of otherworldly and cosmic that I think it's worth taking a moment to try to imagine yourself on the surface,

what you would see. And you can see the geysers against the blackness of space, but if you follow the line, you can see them go onto the night side of the planet. And so if you were standing there on the night side of Enceladus and looking up, you would not be able to see the geyser in front of you on the ground because it'd be dark. It's night. But you'd be looking up into the sky. And at some point, the sunlight would be coming across and lighting up the geyser way up above your head. And so that would be pretty cool too. Quite a light show. Linda, why only the South Pole? Why coming from these tiger stripes?

That's a good question. We think that had the geysers or these fractures start anyplace else, it would naturally move toward one pole or the other. But why just the South Pole and not the North Pole, we're not exactly sure. Although we know the crust is thicker over the north, and maybe it's too thick for this water to get through from the ocean. So one hypothesis is that if you look at Enceladus's next door neighbor, Mimas, it's a similar sized world with an enormous crater on it. And perhaps another, Enceladus received a big whack. Actually, every single one of Saturn satellites, icy ones that you look like, has a great big crater on it. Enceladus doesn't. And

maybe it got a big whack at some hot spot on its surface that got this kind of runaway process of melting an ocean and everything going. And over time, the entire crust of Enceladus rotated to place it at the south pole because of Enceladus's spin. It's quite a story. Why the hot spot, though? What is the mechanism behind that? Well, we think that the reason Enceladus has the ocean is that it's in a resonance with Dione. It makes its orbit slightly elliptical, egg-shaped. That allows Saturn to sort of be squeezing on it like you'd squeeze a ball. And that heat energy then keeps the ocean liquid.

But why not Mimas? I mean, that's another puzzle. Why not Mimas? Earl, Jacob mentioned that by flying through the plumes, Cassini was able to taste them. How? What instruments? Well, there are two instruments that are able to actually analyze the particles in situ. One is the ion and neutral mass spectrometer that can break them apart by their molecular components. And also our cosmic dust analyzer has the ability to do some chemistry on the components.

They can't do chemical experiments. They can only break them apart and decide what they're made of. And both of those we have used to advantage on Enceladus by flying through the plumes themselves. We've been closer to Enceladus, but I'd say it was 2015 we did it. Yeah, we were actually closer, but we were closer. Yeah, but we actually went through the plumes. And that was a bit of a dramatic moment.

One of the videos you showed actually showed some kind of snowflakes hitting on the windshield. That may have been a little bit of artistic license. But there was some concern that we might have some particular particles there that might cause us some harm. But there's no way to, I mean, to fly through the plume and use the high gain as a shield would have been just a complete waste. So we took that chance, and the risk was fairly low. And we did. We started out on thrusters at about 175 kilometers, and then slowly realized that we weren't doing any thrusting. There was no resistance, and then we slowly worked our way down to 25 kilometers on reaction wheels.

So the stability of the picture is being able to get close. Do you want to explain what the distinction is between using reaction wheels and using thrusters, why you have to use thrusters in some situations? Well, thrusters you use to turn faster or to go incredibly fast. You use it for turning fast and for fighting the atmosphere. We use thrusters at Titan. When we go below about 1,300 kilometers, we fight the atmosphere with the thrusters. If we go above 1,300 kilometers, there's not enough atmosphere,

and we can hold the spacecraft stable with the reaction wheels. I have to pile on to that incredibly fast comment. Watching Cassini turns is like watching the hour hand of a clock. You're moving many tons with itty-bitty controllers, and so when we go rapidly fast with the thrusters, it's about three times that fast. Well, okay, all right. It's 30 minutes to do a 180-degree turn. Linda? What was so incredible about Cassini, we actually seven times flew underneath the South Pole

directly sampling the gas and the particles to reveal the ocean, the organics in the ocean, excess hydrogen, tiny nanograins of silica. These tiny grains could only form in water that's near the boiling point, telling us there might be hydrothermal vents on the seafloor of Enceladus. And so tantalizing, you have the water, the energy, the food, the organics. Could there be life in this very intriguing ocean? And you also had caps. You had the mid-range, the plasma spectrometer through Enceladus 17.

Right, right, to see the larger particles. And so not only is this a promising environment in which life could form, it has all the ingredients, the chemistry, the liquid water, the solvent, the energy from the hydrothermal vents, but it's so politely spewing its ocean into space where it's really easy to scoop up. Free samples. Free samples. So, you know, maybe there are other places in the solar system where other people are convinced that might be more likely to have life, but there's none that's easier to sample than this one. So you found organics, but not complex organics because you just couldn't, right? That's right. The instruments on Cassini were not designed to look for life.

So we couldn't find the amino acids, the fatty acids, the long chain molecules that would be created by life. So that's for a future mission. So that's why we need to go back. So would you bet on it? Would you bet that we would? What are the odds? I think the odds are pretty good. It's just a question of what's that initial spark to get life going. It's worth a look, that's for sure. Let's jump to Saturn's neighbor, Jupiter. With any luck in the early 2020s, the Europa Clipper will be leaving for there. And I believe it will be able to taste those longer, more complex molecules, perhaps of life, right? That's exactly right. It has the mass spectrometers with the range, like maybe four

orders of magnitude more than Cassini has to do just that at Europa. And it's just a matter now of finding a plume and flying through it. Now, there are signs that Europa could have plumes, kind of like Enceladus does. The problem is that Europa is much more massive than Enceladus. So those plumes don't travel nearly as far into space. And so it'll be much more difficult to find those things, which is what makes Europa a little bit harder to target than Enceladus, but it's also a lot closer. Plus, you've got that horrifying radiation environment at Jupiter. Earl, would a mission like Europa Clipper work well for Enceladus? Would it in some ways be easier?

Well, other factoring in the fact that Saturn is so much further away, yes. But Enceladus itself isn't. What the Europa Clipper is able to do is to use Europa to effectively move itself around and investigate Europa on all sides. Enceladus would be a little bit more challenging for us because it's so small that shaping the trajectory to go around to the other side, you know, beneath and around the way we've been able to with Titan. So there'd have to be some astrodynamics done with Titan as well. But a Titan and sell this one-two punch, I mean,

what could be better? I mean, it's what we try to do. And to go back and do that even more with even more sophisticated instrumentation would be perfect. We can't give equal time to the other moons, but there are, what, 60-something? There's quite a lot. 62 moons. And all these little ones have their own personalities. But I think one of the things that we learned from Cassini is how connected the entire system is. I mean, all these mid-sized icy moons, Tethys and Dione and Rhea, their surfaces are painted with ring material

that's been accelerated in the magnetic field and implanted, I think, correct me if I'm wrong, on the backsides of these moons. So it's all, you know, they're individual worlds with their own histories, but they're all connected to each other in the system. Right, through the E ring, through the material from Enceladus

that spreads out in the system. Right, through the E ring, through the material from Enceladus that spreads out through the system and coats the far sides, the back sides of these moons. So how much of the E ring is Enceladus responsible for? Enceladus makes the entire E ring. It's thickest at the Enceladus orbit, but it spreads all the way into the rings of Saturn and all the way out to the orbit of Titan. A very water-rich, E-ring-rich system. Where can people go to find more, many, many more images like the ones we've been looking at tonight?

I'm glad you asked, Matt. You can go to the Planetary Society's website at planetary.org. Follow the links to the multimedia and the Bruce Murray Space Image Library, named for one of the founders of the Planetary Society. One of the things that I do at the Society is I try to corral images that have been processed by this huge international community of people who

are thrilled and excited about images from Cassini and all of our beloved space robots. And you really can't find a larger collection of those things anywhere. I'm very proud of it. It's far from just me. There are so many other people who are much better at this than I am and produce amazing pictures. And it's not that the scientists can't produce these things. They certainly can. Just that when science process images, you're usually trying to increase the contrast, trying to look for subtle features, trying to understand, of course, the

science that's in the picture. But the amateurs and the enthusiasts, they're trying to answer the question, what would it look like if I was there? And so you get these unearthly and yet still familiar images that would look like they would appear to your own eyes. And it's just incredible. Do any of you in the purple shirts want to get equal time for a JPL site? Well, You in the purple shirts want to get equal time for a JPL site? Well, I do want to just follow. I couldn't agree more with Emily. The amateurs and semi-professionals that have been processing the data from Cassini have done a phenomenal job, and we do share some of those on our website, saturn.jpl.nasa.gov.

Again, all the raw images are there in their very raw form, as well as some of the science-enhanced images. And we also have given some form to the amateur images, because they really are spectacular. And the patience and precision that Emily and others have put on these images are just, I think, spectacular. So, both places. Right. In fact, Emily was one of the first to put out Enceladus setting behind Saturn.

She very quickly got those raw images, put them together into a wonderful movie, and I think beat anybody else out there. I'm not the best, but I'm the fastest. First is good. Our time has flown by, but we have to ask, what's next? That's a good question. Yeah, I mean, we've given some hints at other missions, going to Titan, going down to the surface again,

getting back to Saturn, but there's so much more that we can do. Is there anything we can look forward to in New Frontiers that you can give us hints about? The New Frontiers program that Jacob mentions, there are actually five missions. They are competing. It's a group of 12, and five of those are to go back to Saturn. There are two Enceladus missions to answer the questions about the ocean,

look for evidence of life, two Titan missions, an orbiter and a quadcopter, a Saturn probe mission, and then so there's five chances. In December we'll hear which of those, three of those, we'll make it to step two, another year of proposal work, NASA will down select to one. And there's also other ideas out there for joint missions with the Europeans. Maybe we could do a Saturn probe mission with the Europeans where maybe we build the probe and they build the

orbiter, for instance, or the spacecraft that carries the probe. Or how about Cassini 2 and 3 to go to Uranus and Neptune? So I think there's a lot of potential, but it might be decades in the future, though, until we get back. I think this is the part of the show where I need to stand up for the underrepresented planets. I would like to see new frontiers go to Venus, finally, because Venus is so neglected. But there are such wonderful targets at Titan and Enceladus. And I also think that we need to keep in mind that Uranus and Neptune are both going through their equinoxes toward the end of the 2040s. And that's a period when you actually get to see both poles of all the planets and their moons. And so I'm hoping that we can plan in the long term

and get perhaps a pair of spacecraft, identical spacecraft that would be out there exploring both of those distant worlds. And they're very different worlds, these ice giants from the gas giants that we've been looking at with Jupiter and Saturn. And yet they're very similar in size, at least, to the majority of the worlds that we've been discovering orbiting other stars with all of our exoplanetary missions.

So a close look at Uranus and Neptune, you're looking actually at thousands of planets, millions maybe, across the Milky Way galaxy. Earl, what would you like to see happen next? We'll stick to the outer solar system. Stick with the plan. As wonderful as Cassini has been at Saturn, I think that we need to keep going. Voyager has shown us, has teased us with Uranus and Neptune.

They're long missions, but we have the capability, both in propulsion and in instrumentation, to get there in our lifetime still. I'm probably going to be on the couch watching TV, but I would like to see us continue to keep that going. There's a strategic view of exploring our system, and at the same time, we want to be tactical and use some of these smaller missions to go back

and look at Enceladus and Titan, but not lose sight of the big picture. Julie, where do you want to go? Well, I'm with Emily. My first spacecraft was Magellan. At Venus. At Venus. So I would like to go back to Venus.

At one time in 1991, we had a better map of Venus than we did of the Earth. So maybe we did such a good job, we don't have to go back. No. I'm really rooting for, is it Psyche? No, that one's a metal asteroid mission.

That's the asteroid. The metal one? Veritas, yeah. I'm really hoping to go back to Venus. How about the three of you personally? Where do you go from here? Let's start with the asteroid. The metal one? Veritas, yeah. I'm really hoping to go back to Venus. How about the three of you personally? Where do you go from here? Let's start with the engineers.

Are you done, Julie? Well, Earl says I'm not. Earl thinks I owe him an engineering report. He knows what kind of writer I am. I've got 20 years of engineering to break down and write about. We don't write papers as well as the scientists do, so we've got a lot of catching up to do. Oh, you can't see them. They're laughing because Emily's shaking her head.

It's really true. But the tension is gone. Absolutely. The tension... I don't want to say the thrill is gone. We. The tension... I don't want to say the thrill is gone. No, we like that tension. We like the tension. I think a month after not being called in the middle of the night, I'll be out looking for another job. Yeah, I've got to get that report for really fast. But I think, you know, I think both of us have been pretty myopic about what's next, just trying to get this done properly.

And now we make some jokes about paperwork and things like that. But I think after the holidays, get ourselves documented up, I think we'll be looking around and we'll see what we find. Linda, speaking for you, yourself, and the other scientists on the mission, you're far from done. Right. We have another year's worth at least, a year's worth of funding, but far longer to actually look at and try and understand all of the Cassini data, in particular the 22 orbits from the grand finale. And I have some data in there too.

I work with the composite infrared spectrometer. There are some beautiful ring scans and I'm looking forward to diving into the data, looking at these things called C-ring plateaus, these thicker regions in the C-ring and higher resolution than ever before. And I'm also on a proposal, one of these proposals for new frontiers.

It's called Enceladus Life Finder or ELF to go back to Enceladus. And so who knows? Maybe in December I'll be one of those three working on another proposal. If not, I'll root for whatever mission NASA picks. Are the citizen scientists going to keep digging through everything that's come back? And, you know, the Cassini mission was very generous to share those raw images on the Internet, but they were actually kind of a cruddy version of the data set. They were not calibrated. They were squashed down with JPEG compression. It was kind of gnarly.

And so now my hope is that I can encourage more of the amateurs to go into the NASA archives, use the real science quality data, because there's so much more subtle detail available in those images that anybody's been able to appreciate from the raw JPEGs. And so my goal, I think, is to encourage more people to participate in that kind of image processing. Linda, do you have an idea offhand of how many papers have been based on Cassini data and how many PhDs have been achieved? Well, we have over 3,000 science papers so far. And I'm sure in the next year and

in the decades to come, there'll be far more papers and books. We've literally rewritten the books about Saturn and Titan and the rings and probably dozens of PhD theses. I don't know the exact number. And those will continue as well with this very, very rich data set. So just as you were a fairly young scientist, a PhD when this got started, it's a good way to bring the youngins up. Oh, absolutely. I've had some wonderful postdocs that have worked with me over the years. In fact, my very first postdoc is now the project scientist for the Huygens component of the Cassini mission. I tell them, I'm so proud of you. This is great. We have sadly reached the end of the evening. I want to thank all of our guests for being here, and excuse the four of you.

Please help us thank Planetary Society Senior Editor Emily Lakdawalla, Cassini Mission Manager Linda Spilker, Cassini Mission Program Manager Earl Mays, and Cassini Mission Spacecraft Operations Manager Julie Webster. And that is along with the 5,000 scientists, engineers, and others who have made the Cassini mission one of the greatest voyages of exploration ever. And we'd like to give a special thank you to Caltech's Beckman Auditorium for hosting us, NASA and JPL for all those wonderful images you saw up on the screen, KPCC's in-person team, the Planetary Society,

thank you to all of you, and to Matt. It's been fun. My co-host, KPCC science reporter Jacob Margolis, closing out our spectacular celebration of the Cassini mission. But wait, there's more. We actually ended the evening with a great music video about the mission and its grand finale. You'll hear it right after our visit with Bruce. You can also see the entire evening titled Destined to Crash, Cassini's Grand Finale, including all of the great images. We've got the link on this week's show page at planetary.org slash radio. We finish up with what's up, and that means that Dr. Bruce Betts, the Director of Science and Technology for the Planetary Society, has joined us once again. Welcome back. What's up in the night sky?

The exciting thing going on is Venus and Mars in the pre-dawn. That's the pre-dawn east. Venus is the super bright object. east. Venus is the super bright object and Mars is coming up from below it, getting closer and closer each day until they are really, really close on October 5th. And then they'll begin to separate again. We've also got Jupiter and Saturn in the evening sky. We move on to this week in space history. It was 10 years ago this week that the Dawn spacecraft launched and then went off to explore Vesta and now Ceres. Big asteroids.

Yeah, big asteroids. We'll be talking to Mark Raymond. I think in two weeks, we're going to have a conversation with the chief engineer and mission director for Dawn. It's already in the can. A little update on that mission. All right, we move on and we've got a special help, don't we? We sure do.

You know, we love it when we get a little help from listeners. We do indeed. Yeah, to introduce Random Space Fact. This came from Jeremy Kocal. I hope I have his name pronounced. I hope I pronounced it correctly. I will mention up front that he's a big fan of yours. He took your course.

Oh, cool. Actually earned a certificate in doing Bruce's periodic intro to astronomy course offered by Cal State Dominguez Hills. People can still see that, right? They can. You can find it at planetary.org slash Betts class, B-E-T-T-S class. In addition to being now a certificated astronomer. Well, I'm not, yeah, sure. Congratulations, nonetheless.

Okay, Jeremy is also the tenor in a group called the Moon Rays, which he describes as Southern California's premier doo-wop group. And these guys do a lot of top stuff. You know the Dapper Dance, the barbershop quartet at Disneyland. I used to love to listen to them when I worked there. They have Broadway careers, some of them. They do all kinds of stuff. They've even been on stage at Coachella.

So here are the Moonrays with their random space fact intro. We got a random space fact, random space fact, random space fact. Random space fact. That was very cool. Thank you, Jeremy. Thank you, guys. That was lovely. All right, I'm not done with Cassini.

The Cassini spacecraft, over its 20-year mission, traveled the equivalent of nearly 200,000 times around the Earth. Holy cow. That is impressive. You've honored the moon race with a wonderful... Sorry, I guess I should have done something moon-related. I didn't connect it all together. Speaking of Cassini, we asked on what rocket did the Cassini spacecraft launch in 1997?

How'd we do? Got a huge response for this. Just people love Cassini, I suppose. Random.org picked longtime listener, first time winner if he's got this right, Kevin Nitka of Forked River, New Jersey. He says, Cassini launched on a Titan IV-B Centaur on October 15, 1997. That is correct. Kevin, congratulations. He went on to say, a truly wonderful experience from launch to end, and all the Cassini gave thanks to all who made her and kept her for all mankind.

Kevin has won himself a new Chop Shop Design planetary radio t-shirt. You can see those at chopshopstore.com. There's a whole Planetary Society store there, sub-store, and a 200-point itelescope.net astronomy account from iTelescope, the non-profit worldwide network of telescopes that anybody can use. 200 points is worth a couple hundred dollars U.S. Eric Bruner of Cary, North Carolina, says that Titan was the last lunar or planetary mission to launch on one of those now-retired rockets. That also put the Vikings, the Voyagers, Mars Observer, and Clementine, the mission to the moon. Those were apparently all on Titan rockets, Titan variants of Titan rockets.

We had a whole bunch of people, including Pepe Smith in Hong Kong and Jordan Tickton, much closer in San Luis Obispo, who all noticed that it was a Titan that was sending a probe to Titan. How appropriate. Mel Powell of Sherman Oaks. Of course it was a Titan rocket, because it would have been darn silly to send a spacecraft to Saturn on a rocket called Ganymede.

And challenging. Let's see. Eric O'Day was one of those watching the grand finale. He was at the Museum of Science Boston for that big finish, said there was nary a dry eye there. And finally, this from Kay Gilbert, not our poet laureate, but Kay in Manhattan Beach. The Titan IV-B is no more.

Goodbye to its liquid-fueled core. The Centaur Stage III deployed Cassini, assuring its place in space lore. Thank you, Kay. We're ready to move on. I don't often ask for definitions, but I think this word is often misconstrued, so let's learn a little something. What is the definition of the metallicity, metal! Metallicity of a star.

Go to planetary.org slash radio contest! Are you doing the devil's horns when you say metal? Maybe. You know the story of those? It's rather fascinating, but unrelated to our show.

Yeah, we'll do that on our other show. You've got until Wednesday, October 4th at 8 a.m. to get us the answer to this one. We're going to give away again from Chop Shop, not the Planetary Radio T-shirt, but the just as, if not more, cooler Planetary Society shirt. The one we talked about last week, the Venn diagram of Mars and Earth that says Planetary Society at the intersection. A 200-point itelescope.net account. And then, ah boy, these artists have waited so long for this. Finally, we're going to start for the next several weeks giving away beautiful original art. Well, they're prints, actually, provided by members of the International Association of Astronomical Artists. We've had

them on the show a few times, representatives from there. You can read about the association at IAAA.org, I-A-A-A.org. This one from Simon Kriegar. Simon, who's a good friend of the show, he has provided a couple of prints. We're going to give away an absolutely gorgeous print from Simon of the lunar module, Apollo lunar module, in its last few moments before setting down on the surface of the moon. It is gorgeous, and it could be yours if you're chosen by random.org and have the answer correct. Well, that's very, very cool. Yeah, it really is pretty.

All right, everybody. Go out there, look up at the night sky, and think about dog licks all over your face. Thank you, and good night. I'm sorry. I really hate that. And our dog knows not to do that to me. He goes after my wife. That's Bruce, dog lover extraordinaire and director of science and technology for the Planetary Society, who joins us every week here for What's Up. By the way, you can see lots of Simon Kroegar's work at SimonKroegar.com. That's S-I-M-O-N-K-R-E-G-A-R, all one word.

Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its awesome members. Before you go, we have a special treat from a local band, the Amoeba People. They make great music and they love science, so it shouldn't be surprising that they have created their own tribute to the grand finale. I think some of the band members are here tonight. Ladies and gentlemen, boys and girls, Saturnians and Titans, here is the Amoeba People's Cassini Dive Go.

Good night, everyone. Clear skies. Thank you. Thank you. Got to take it back, back to 1997 When Cassini left the Earth for good With the one-way ticket for a seven-year journey Bound for Saturn and its neighborhood Destination, the jewel of the planets Had to leave the Earth far behind

But little did they know The success of the mission would leave it in such a bind. Oh! Cassini Dive Go! Oh! Cassini Dive Go! Gathering data and sending it back. Information like we've never seen. Thank you. One last dive through Saturn's rings, then it's time to light up the sky. Oh, Cassini dive, go! Oh, Cassini dive, go! Oh, Cassini dive, go!

Oh, Cassini divego When the mission's all done And the data's collected Enceladus will need to be protected When the mission's all done And the data's collected Enceladus will need to be protected To avoid contamination And the risk of pollution A grand finale is the only protected to avoid contamination and the risk of pollution

a grand finale is the only solution to avoid contamination and the risk of pollution a grand finale is the only solution only solution yes only solution yes if that's so let's put on a good show Oh, Cassini dive, go. Oh, Cassini dive, go. Oh, Cassini dive, go. Oh, Cassini dive, go.