Planetary Radio: Space Exploration, Astronomy and Science - The Final Countdown at Saturn

Episode Date: January 31, 2017

Planetary Radio’s most frequent guest, Project Scientist Linda Spilker, returns with another update on the Cassini mission that is approaching its grand finale.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

The Final Countdown at Saturn, 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. She's back. Our most frequent guest, Cassini Project scientist Linda Spilker, is here with another report on that magnificent mission as it enters its last months. It includes Cassini's top 10 science discoveries for 2016. Bill Nye sees political momentum building toward a human mission to Mars,

which is where we'll join Bruce Betts standing on top of the solar system's biggest volcano for his What's Up segment. Emily Lakdawalla is the Planetary Society's senior editor. Emily, big news in your most recent blog post. Not the kind of news we typically get from you there, and the last one we're going to see for a while, I take it. You know, it's been about four years that I've been working on a book about curiosity, and I finally had to face the fact that I was never going to finish it. I was never going to catch up with a rover if I didn't stop everything else to finish up the book. So I'm taking a three-month sabbatical from most of my other duties at the Planetary Society in order to wrap up work on this enormous tome on the Curiosity mission. on the Curiosity mission.

Now, I remember when you first told me that you had been asked to create this new book, and I thought, wow, it's kind of early to be writing that. Don't the additional two years sort of help a lot with what you're going to be writing about? Well, they do, especially in that they allow me to talk about a more interesting part of the mission than the first year of the mission when they were mostly working the kinks out,

although they did make some important discoveries at Yellowknife Bay. But now I have a whole rover traverse to write about, the beginning of the march up Mount Sharp. And so the science is definitely going to be much better than it would have been had I turned in my manuscript and it was originally due two years ago. I'm not the only one hearing this who is going to miss you for those three months. And I'll look forward to your return. But it's not like we're just going to fly over this segment. We've got lots of other good folks that will give a chance for their voices to be heard in your stead. For example, Jason Davis, our colleague at the Society. That's right. And there will hopefully be other guest voices as

well, along with all the other guest voices on the blog that I've been cultivating for the last year and more, trying to get more diversity in points of view on what's happening all across solar system exploration and designing the machines that we need in order to do it. So it definitely won't stop. It just won't have me for a little while. Those of you who regularly refer to Planetary.org for news about planetary science, and much more nowadays, probably have noticed that over the last year or a little bit more, we really do have a much more diverse group of voices, not just in topic, but the sorts of folks who are writing for us. And Emily, I thank you for that, because I think it really has become a great place to find out what's going on in space. Thank you, Matt. You're welcome. And good luck with this effort with the book. And we'll have you back when it comes out, of course.

I hope you'll be on the show long before that, returning to your regular segment. But I really look forward to reading the book and talking to you about it when it comes out. Believe me, Matt, so do I. That's Emily Lakdawalla. She is still the senior editor for the Planetary Society, our planetary evangelist. Just going to do that evangelizing in another track for a little while. And she's a contributing editor to Sky and Telescope magazine. Bill Nye is her boss. He is the CEO of the Planetary Society. Bill, big developments this week.

For people who want to get humans to Mars, particularly Americans, I suppose, you shared this article by Mark Kelly, among others, on Wired.com. We'll put a link to it up on the show page. Put people on Mars by 2033 for the good of the nation. Yeah, it's not just Mark Kelly. It's also our own Scott Hubbard, the Mars czar who's on the board of the nation. Yeah, it's not just Mark Hill. It's also our own Scott Hubbard, the Mars czar who's on the board of the Planetary Society. And the idea is that people have proposed going to Mars for decades,

but the timeline is always extraordinarily long. As you may know, the Planetary Society convened a meeting, Humans Orbiting Mars 2033, where we did a very diligent analysis of a reasonable architecture, series of rockets and space habitats and solar electric propulsion cargo trips that would put humans in orbit around Mars in 2033. put humans in orbit around Mars in 2033. And 2033 is significant in that it's a reasonable and possible orbit, with the Earth's orbit and Mars orbits lining up in such a way that you could get there economically and quickly. And so this article proposes having humans land on Mars in 2033,

and that would involve just going two orbits earlier, 2028 in orbit. But this could be done. And the idea of the Planetary Society study was that you wouldn't have to increase the budget for NASA. You just have to retire the space station per the agreements or hand it off to somebody in 2024. And then you could do this, and everybody would be engaged. And if the United States were to do it, the United States and NASA would remain the world leader in space, and that's the appeal of this article. And we're all for it.

Now, if you want to lower the cost even more, you have an international effort with many space agencies and aerospace companies working together to put humans in orbit and then humans on the surface of Mars. It'd be fantastic. It would speed up everything. It wouldn't be that much more money than we already spend around the world, and it would change the course of human history. Is that a big deal? Kind of. Let's go. The article, once again, it's in Wired.com. It appeared on January 28th. And it's by an astronaut, Mark Kelly, Scott Hubbard from the Planetary Society Board, the former Mars czar.

And good credit to Norm Augustine as well. Known for the Augustine Commission. These three guys are the real thing. So we're very hopeful that this will pick up momentum. John Culberson from Texas, the congressman from So we're very hopeful that this will pick up momentum. John Culberson from Texas, the congressman from Texas, is very supportive of this. And so we'll see if we can, as the saying goes, get her done. Thank you, Bill. Thank you, Matt. That's Bill Nye. He says we should be off to Mars. And he is the CEO of the Planetary Society. We've been at Saturn for years. We're

going to get another update from Linda Spilker in this last year of that spectacular mission. Moments away. September 15, 2017. That's the day one of the longest, most successful, and most exciting planetary science missions will meet its spectacular end. Cassini has astounded us throughout its 12 years exploring Saturn, its rings, and its moons, and the best may be yet to come in the barely seven months left

before the school bus-sized spacecraft plunges into the planet's atmosphere. Linda Spilker is already preparing for that fond farewell. Planetary Radio's most frequent guest is the Cassini Project Scientist, coordinating research underway by mission scientists across our world. Cassini has been a big part of her life for decades, just as the Voyager mission was even more years ago. She dropped by Planetary Society headquarters late last week. Linda, welcome back to Planetary Radio.

Matt, it's a pleasure to be here. And here we are at the beginning of the end. That's right. Which we'll talk about more later. We've talked about the grand finale coming up in September in the past. Gosh, it's just, it's sad. Sad, but exciting. I agree. I agree. It's sad, but the awesome science that's left to come back from Cassini makes it all worth it. I couldn't agree more. Let's start talking about what's going on with this grand mission in its grand finale year. Where is Cassini now? We're in a set of what we call ring-grazing orbits.

We went into these orbits the end of November. What we do is we pull in the closest approach of Cassini very close to the outer edge of the F-ring, closer than we've ever pulled in before. And this is so cool. We have 20 orbits, and we get incredible views of the tiny ring moons of Saturn and the best ever views we've had of the outermost rings themselves, the A ring, the gaps that are there.

And it's just amazing, the pictures and the data that are coming back. I want to get your comments about those ring moon images, which anybody who heard last week's show knows that I talked with Emily about those in her short segment. They're mind-blowing. I said to her there's that one of Daphnis where there's that little filament kind of coming off into the path of the moon or behind it. And what I said to Emily was I'll repeat the line. I said, Stanley Kubrick called from beyond the grave. He wants to use these images in his remake of the trip sequence in 2001, A Space Odyssey.

That would be great. If they ever do a remake, they're definitely welcome to use it. Yeah, that Daphnis image is incredible. Here's this tiny moon. It's only 8 kilometers across. It's clearing a gap about 42 kilometers wide. And if you think of it in terms of the 240,000 kilometers of the ring, And if you think of it in terms of the 240,000 kilometers of the ring,

this is just a very tiny piece of the ring, and yet this moon is in a mighty way is opening up the gap, and it creates waves on the edge of the gap. You can see Daphnis pulling ring particles in. There's a ridge around what looks like the equator of Daphnis, even craters on one end of the moon. So clearly some of the bigger ring particles must come in and collide with Daphnis every once in a while. We'll post some of the images, but we will post links to some of these as well once again

because they really have to be seen. Oh, it's stunning. I mean, Daphnis has gone from this point of light to this world that you can actually see, this sort of potato-shaped world. Yeah, yeah. Like so many things in our solar system that aren't big enough to be round. It's potato-shaped is a really popular theme. That's right.

How about the spacecraft, the health of the spacecraft? There was a great entry on the website about, I think it was the care and feeding of a senior spacecraft or something like that. You've been up there a while. That's right. That's right. By the end of the mission, 13 years in orbit around Saturn and another seven years of crew. So basically 20 years since we launched Cassini. And we've just been so lucky. The systems are all working well. You know, we've had some trouble with some of the instruments. But overall, really a very healthy spacecraft and all of the instruments, except for one, the plasma spectrometer, are on and taking data and working. So just amazing.

And way beyond the expected life or the life everybody hoped you would get. Right. The warranty has expired, and yet we're still going strong. Yeah. One of the numbers that I just was amazed by in that article, it said 6 billion reaction wheel rotations, those things that use inertia to steer the spacecraft, 6 billion. And for anybody who isn't impressed by that, remember, in the vacuum, in bitter cold. That's right. That's right. It's right. It's just amazing that they're all working, and we use those reaction wheels to point the spacecraft,

point the cameras, point our instruments into the direction of incoming dust. So we use them all the time. You have this revelation, which has only come in the last couple of days, as this show is heard, as it's being heard by the first listeners, more stunning images because of where the spacecraft is now. That's right, Matt. In these ring-grazing orbits, we've now turned our cameras to look at the outermost part of the rings, the A ring and the B ring. And we're seeing things down to a quarter-mile resolution, twice as good as anything we saw at Saturn Orbit insertion, which were the very best pictures of the rings previously.

We're seeing straw, we're seeing propellers, we're seeing density waves, just an incredible set of new images that are out there. And there's more to come. These images are all taken on the unlit side of the rings, so it's pretty dark there, especially in the B ring. So our exposures are a little bit long. There's a little bit of smear. But the images we're showing, we've put them out in the raw data format.

So those little bright spots that you see are cosmic ray hits or just hits on the camera. But it allows you to see incredible, exquisite detail. I just love that straw, these clumping together of particles that make these long filaments of ring particles that may be ephemeral. They may come and go. It's just so amazing. Straw is back. It's cool to see. And this is one of those times when I regret that it's not radio with pictures

so that you could narrate the little slideshow that you did for me just before we started recording. All these incredible structures, the straw, the so-called propellers, which I guess we're seeing much smaller ones now than seen in the past. Right. We're seeing little tiny propellers. We saw hints of those at Saturn orbit insertion. And these propellers tend to form in belts. What they are is some of the largest ring particles. They're trying to open up a gap, but they're not quite big

enough to do that. So they open up a little partial gap. And this looks then like two arms of an airplane propeller. And we see those in the images that are posted as tiny white streaks. And we know that they're objects, sort of the largest end of the ring particles creating these propellers. You also pointed out, God, an image which I was looking at on the train in today, because it just captured my imagination, of this wake structure, these alternating lines of particles, which you have been studying for many, many years. Actually, I wrote my PhD dissertation on the waves and the wakes in Saturn's rings, these spiral density waves created by resonances with Saturn's moons.

That just means if the moon goes around once and the ring particles go around exactly twice, you can get energy to create these waves that damp out and you get this incredible structure. Imagine waves sort of crashing together and then pulling apart. And this is creating in the strongest part of the wave, the straw that we see. It's actually pushing the particles together so it's easier for them to clump together and then pulling apart. It's just amazing in these density waves to see so much straw. And then the moon pan inside of the Encke gap creates wakes on each side of the gap, and then these wakes propagate out into the rings. And part of what I worked out for my dissertation is how far do these wakes propagate? And now we're seeing in the images just beautiful

structure of one of the pan wakes that propagates for a long distance away from the center of the gap. Just remarkable, awesome to look at. Before we move on, there's one other moon I think you want to talk about. Right, we got some of our best ever images of this moon named Pandora. It's the outermost of the Eph-ring shepherds. It's about 50 kilometers across. And we really see incredible structure. We see craters. We see ridges. It's clearly coated with icy particles from the F-ring. One of the large craters, you see a bright region. Maybe the ring particles slid down and we're seeing the icy core that's underneath Pandora. And Pandora can only get coated with so many ring particles because its gravity, once it gets balanced with Saturn's gravity,

then the ring particles can't stick anymore. We call that sort of the Roche radius or the Roche lobe that it fills. And so that gives sort of a maximum size to get coated with ring particles. Some of these tiny moons that almost have a skirt of material that go around their equator and that forms more, accreted more around the equator. But the Pandora images are stunning as well. Yeah. These little ridges or depressions on the moon, which are not very many kilometers wide. That's right. That's right. Maybe some of the largest particles, we call them parent bodies

in the F ring, maybe sometimes one of those makes it out and has a collision with Pandora. Fascinating. We also have to mark an anniversary that took place in December, and it sure makes me feel old. It's been 12 years since the Huygens probe from the European Space Agency descended to Titan. That's right. Cassini released the probe in December 2004, and Huygens landed on the surface on January 14th of 2005. Huygens is still there. You know, Huygens was running on batteries,

and those batteries have long since no longer functioning, but Huygens is still there. And as Huygens was parachuting down to the surface of Titan, gave us our first look at what the surface of Titan might be. And in a certain sense, Huygens is the Rosetta Stone, that data to help us understand the data that we're now getting back from orbit, to actually have data on the surface and now be looking at all of Titan with the orbiter. Huh. So it plays, obviously, an ongoing role in helping with this radar and other data that

you're still gathering. That's right. To help us understand with the Huygens data, we saw the first images of what looked like river channels flowing down. And then those rounded icy pebbles where Huygens landed told us that fluid was flowing on the surface of Titan. So, so much we learned just from that landing, the first robotic emissary in the outer solar system.

Now, we're going to come back to a lot of this because we have sort of your top 10 of 2016, which has been done for many years now with the mission. But first, what's next for the mission? I mean, before you go plunging down into that big planet. Well, on April 26th, we have our first pass through the gap between the rings and the planet. We have our final Titan flyby just a few days earlier. And that flyby actually gives us enough energy to go from just outside the rings all the way across, plunging through that gap. And on that first flyby through the gap, we're going to actually point the high-gain antenna into the direction of any incoming ring particles to protect the rest of Cassini behind it.

It's a shield. That's right, a shield just in case we're not sure exactly what the environment is like. We think it's safe. There's a weak radiation belt in there. If there were too many ring particles, it would mask the radiation belt. So we think we're safe, but just in case, we're going to fly with the high-gain antenna pointed in that direction as a shield and then go back, quickly look at our data. We have radio and plasma wave data, these long antennas, and the particles hit those and give us a signal. We'll be able to tell something about the frequency

and perhaps even the size of those impacts and help us understand, do we need to do this every time for the remaining 21 orbits, or can we go ahead and do the gravity measurements and look at the planet, look at the rings, as we already have put together in our plans. And this is when you'll have the chance to get these new views of the rings from the sunlit side. Right. We'll get to see the rings from the inside out. Imagine what that would look like. We even have a sequence of images looking outward on the rings

as they're closing up as we pass through one of those times through the gap. And the innermost rings, we'll see those in a detail we've never seen before. Best case, when will those images be available since you'll have to turn the spacecraft, that big antenna back from being the particle catcher to communicating with Earth? Right. Well, as all good scientists do, we continue taking data after that plunge through the rings and look at the rings and the planet and collect a lot of data, and the signal finally comes back to the Earth. On April 27th, it'll be a little after midnight Pacific time,

and that's when we'll start to send back the first data and the first images, and we'll be gathered, some of us at JPL, watching for that first signal, saying all is well, and on we'll go for the next 21 orbits. Which I think is going to be a tremendous event in itself. But nothing is going to compare with what's coming in September. That's right. September 15th marks the final day of the Cassini mission, September 15th marks the final day of the Cassini mission, and we're doing this to protect two ocean worlds. Cassini, in a sense, is a victim of her own success. We've learned so much about Titan.

We discovered the geysers coming from Enceladus. Titan has a global ocean underneath its icy crust, as does Enceladus. We've learned that Enceladus' ocean is salty. There are so many things that make us think perhaps it could be habitable. So we don't want to crash Cassini accidentally. We're running out of fuel, which is why we're ending the mission. And when we launched Cassini, we didn't sterilize it in any way. We didn't think we had to when we launched. So just in case, we want to be safe. And so on September 15th, around 5 a.m. in the morning Pacific time, Cassini will actually go into the atmosphere of Saturn. We get a gentle distant nudge from Titan. We call it the goodbye kiss. And this distant flyby is enough to push our closest point deep into Saturn's atmosphere.

And at that point, the Cassini spacecraft will vaporize and burn up. But we'll be watching in those final moments for that heartbeat from Cassini, those final precious bits of data about the composition of Saturn's atmosphere as she goes on into Saturn's atmosphere. That may be a kiss, but I think it's one of those mafia kisses. You know that a lot of us will be up and early in the morning, for a lot of us Europeans, you guys are going to have it much easier, tracking that moment by moment. That is just going to be amazing. And I sure hope that this place, the Planetary Society, will be able to join in the fun. place, the Planetary Society, will be able to join in the fun. Oh, absolutely. Absolutely. It should be just tremendous. It's sad to say goodbye and yet celebrate this incredible, successful mission. Cassini Project Scientist

Linda Spilker will return with 2016's top 10 science stories from Saturn. This is Planetary Radio. 2016's top 10 science stories from Saturn. 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.

In less than eight months, it's fuel exhausted. The great Cassini spacecraft will plunge into the planet it will have circled for 13 years. Cassini project scientist Linda Spilker has already told us what to expect in the time left. All right. For at least the podcast listeners, we're going to go on now to your top 10 for 2016, something the mission has done for many years, actually. You've laid them all out here right off of the website. We'll have a link to this as well. Let's go through these. I mean, we won't dwell on any of them for very long, but let's start with number one. Oh, well, the first one for 2016 is that we now know that the seas on Titan, those seas at the north polar region, are methane rich. Some of those seas are larger than the Great Lakes of the Earth, and we now know that the major composition is methane, liquid methane, with perhaps some ethane mixed in. And so I've been telling people for years, oh yeah, methane and ethane, but it's mostly methane. Right, right. And what we don't know is it might be slightly different from sea

to sea. And so we're checking into that a little bit as well. Maybe some of those seas are perhaps fresher and maybe have more methane. We know that methane basically performs the role that water plays here on the earth. You can have methane clouds, methane rain, methane flows through river channels. So there could be some differences, and we're looking into that. So I know I said we'd do this quickly, and we will, but I've got to ask, how do you use radar to tell what the material is, what the seas are made of? the seas are made of. The radar is actually key in helping us understand how much methane, because we actually sent a radar signal through the sea to the bottom and got a reflection up from the bottom. And if you had too much other material that would scatter the radar signal, and so the fact that we got all the way through to the bottom and then a signal back up gives us

some clues that you have to have a pretty pure methane lake to be able to do that. Okay. Number two, interstellar dust. Who'd have thought? Right. It turns out that in looking at these just tens of thousands of particles that have been collected by the Cosmic Dust Analyzer, 36 of them are interstellar dust. And we've measured their composition. We can tell by their velocities and where they're coming from. And they're different a little bit than the particles we see in the Saturn system. Now, Cassini is the first spacecraft that's been able to measure the composition. We've seen interstellar dust before.

But their composition appears to be not that much different than a solar composition. But these particles are going so fast, if they didn't hit the cosmic dust analyzer, they'd continue right on through and out of the solar system. They just pass through. They're going so fast. They pass right through. They're on flyby missions. Okay. Number three, surprises about the rings. Right.

It looks like the really opaque areas, the places that we don't see any sunlight when we look at the unlit side, may not be as dense as we first thought. And we're really puzzled about that. It turns out with some clever processing, with some of these stellar occultations, we're able to see some of these density waves and actually find a couple of them in the B ring.

And this tells us something about the mass in that region of the wave, at least. And it looks like it's a lot less massive, maybe not that much more massive than the A ring, which was a surprise. So you're wondering, how can we do this? Well, a good analogy might be, you know, a fog, if you're looking through a fog, it can block the trees and the scene behind you, even though the fog is very tenuous. And yet a swimming pool, which has a lot of water in it, you can see through all the way to the bottom of the swimming pool. So maybe something we don't quite understand is going on. But we're going to find out. In the grand finale orbits, we'll measure the mass of the rings, currently uncertain by about 100%.

Wow. You know, if you could scoop up all the ring particles, they'd be about the mass of Mimas. But are they two Mimas masses? Half a Mimas mass? We don't know. And if they're less massive than we think, they're going to be young.

Maybe a comet or a moon got too close to Saturn, got torn apart. If it's more massive, maybe they could have formed at the same time as Saturn and lasted through the micrometeorite bombardment that would slowly erode them away. So we'll find out at the end of the mission. And that in itself, that gigantic complex structure of rings, that the whole mass of it is this one little moon, Mimas. Remind me again, how thick is the ring structure?

Remind me again, how thick is the ring structure? The rings that we are finding as we get more and more data are maybe only as much as 3 meters, about 10 feet thick. Just paper thin, spread out across miles and miles and miles. That's just crazy. Yeah. Saturn is so oblate, it just sort of squishes everything down into this plane. And so that's why at Equinox, anything that's stuck up above this three meter thick ring casts long shadows. Absolutely amazing. All right, we'll keep going. That great hexagon, it just sticks around, but it changes colors. It's a chameleon. Right. This hexagon, this jet stream at the North Pole of Saturn, about two Earth diameters across,

at the North Pole of Saturn, about two Earth diameters across. We're finding that the interior is slowly changing color. As the sun has come up and is now shining down on the hexagon, the hexagon looked very blue for a long time because the haze particles, when the North Pole was in shadow, those haze particles weren't forming as fast. The sun comes up, provides the energy to form the haze, and that golden color is slowly coming back. But why you have a six-sided jet stream that's lasted since the 1980s at least, we don't know. It's an interesting puzzle. The only place in the solar system with a six-sided jet stream. We haven't talked about Enceladus, but it's time to do that.

Enceladus is very fascinating. We know that depending on where Enceladus is in its orbit, it releases more particles. And what we're wondering is, does it also release more gas? And so we planned a distant occultation by a star. The star went behind the jets coming out from Enceladus. And initially we found that the gas density, when the particle density went up, the gas density didn't appear to go up that much, maybe 30% or so. But then the star got close to the surface and went through one of the jets, and all of a sudden we saw a factor of four increase in the amount of gas. So maybe what happens is Enceladus goes around its orbit, and perhaps

coming from these individual jets, there's a lot more gas and that can lift a lot more particles. And so those two really are in agreement with each other. But it really took this occultation very late in the mission to be able to tease out those interesting facts. Is there a guess as to why it's when the moon is farthest from Saturn that the most particles are released? Well, the jets are along these four linear fractures we call tiger stripes. And so in looking at how the squeezing and pulling apart goes as Enceladus orbits, it turns out that its most distant region, maybe those fractures are being pulled apart. And when Enceladus gets in close to Saturn, they're squeezed together.

So you've got this pulling apart and squeezing together, and that may have something to do with how much gas and how many particles can actually go out into space. I just thought of, for some reason, you know, when you take the neck of a balloon and you stretch it and you can make it sing. Yeah. Titan, you've brought it up a little bit. Such a dynamic world.

Right, such an interesting world. And, of course, it up a little bit. Such a dynamic world. Right. Such an interesting world. And, of course, our atmospheric modelers were busy at work making predictions, predictions about Titan's weather. And one of those predictions is that as we got closer to summer, we'd see all these clouds forming in the northern hemisphere, forming over the North Pole. And instead, we found remarkably clear skies. So clear, in fact, that we got some really nice images, both in the visible and the near-infrared, down to the surface. And looking at the lakes and seas, we could see what looked like some kind of a rim of material around the seas. But now, finally, clouds. We're starting to see

clouds and actually have made little movies of the clouds rotating at the North Pole of Titan. So it took a while. It just means the modelers are scratching their heads and going back and thinking, let's see if we can explain this, why it took so long to have clouds. Too bad Voyager missed those clear skies. And you're watching this happen over a period of hours, right? Watching these clouds form like we can here on Earth. That's right. They can form very quickly and dissipate just as quickly. And so we actually have special sequences where we just go and we stare at Titan,

maybe for 10 hours or 20 hours, and just watch. And if the clouds pop up, we can watch them then rotate around and watch them as they appear and disappear. So it's a very interesting way to look at the clouds. We've got to go back to that world. Oh, I agree. I agree. Titan, Enceladus, a probe into Saturn. So many things left to do. That was number six. Number seven, we're still at Titan, and we're still with clouds.

And another big surprise. We found this ice cloud that formed in Titan's stratosphere at the South Pole. We're looking at it and we found a compound, a very unique compound called dianoacetylene that formed into, in order to form it, it just doesn't form by itself. You actually have to have a coating or special particles of ice that form to have a cloud of this composition. Voyager saw a very similar cloud and it was only with Cassini data and lab data, too, to best understand it, that we could figure out what was going on with these unique particles of ice in Titan's cloud. So this is still another mystery yet to be solved.

Right. I think we've answered lots of questions with Cassini, but I think we're going to leave a whole lot of questions for future missions to answer. That's science. All right. We're still on Titan, and this is one I know we did talk about, not only with you but with other people, about surface features on that world which make it look even more like parts of our own planet. Right. And going into these lakes are these river channels. And these river channels

are very narrow canyons. And it turns out that not only could we probe the depth of the Titan Seas with the radar, we're actually able to probe the depth of the liquid in the canyons flowing down. These canyons are very steep-sided and very deep, anywhere from 250 to 600 meters deep of fluid flowing into these lakes. So we now know they're feeding the seas. And so remarkable that we actually were able, with pinpoint precision, to hit the radar signal across some of these canyons. You haven't seen any kayakers? No, not so far.

It would be interesting to kayak on tight. I've seen that kind of stuff, fanciful images of that. We're down to number nine or up to number nine. And it's about Saturn telling us more about the moons? Right, right. Some recent estimates have been done about how quickly the moons might move outward from Saturn. And we call this migration of the satellites. And it looks like it might be quicker than we originally thought. And if this migration is happening rapidly, then that tells us that perhaps Saturn's moons are much younger than we originally thought. Maybe they didn't form at the same time as Saturn formed, but formed much later, perhaps from material coming off

from the rings, perhaps through some other process. So there's just this one idea. Not everyone, of course, is in agreement with the interpretation, but it's a very interesting model that perhaps the moons are much younger than what we originally thought. And finally, number 10. Well, 10 is about the dramatic seasonal changes on Titan that were, as we've gone from basically southern winter solstice now toward northern summer solstice, we've just seen remarkable changes that you have weather on Titan. And it's a very Earth-like and very interesting looking world as well.

And just to have been there for almost two seasons is what gives us the opportunity to make these kinds of observations and put the pieces of the puzzle together to understand a place like Titan. So half a Saturnian year, what would you give to be able to send it out for another two seasons and finish out a full year? Oh, if only we had enough fuel to last, say for another 10 years or another two seasons to complete one Saturn journey around the sun. I'm sure we'd make more remarkable discoveries, maybe a chance to fly through the Enceladus plumes a few more times and just continue to sort of understand and reveal the planet,

the rings, the icy moons, and just what's going on at Saturn. And that would be so wonderful. If we had solar power, maybe we could have lasted longer. But the real constraint is the fuel. That fuel light is on, and it's telling us that it's time to figure out the best way to say goodbye. That's the 2016 top 10 hits from the Cassini mission. Certainly not in any way all the science that came back, but just this group of fascinating stories, which again, you can find at the website. And we'll have a pointer to it on this week's show page that you can get to from planetary.org slash radio. Linda,

we got to talk at least, oh, I don't know, a couple more times before that big finish? Oh, absolutely. Absolutely. Maybe right before more times before that big finish? Oh, absolutely. Absolutely. Maybe right before or right after that big plunge in April. Thank you also for, you allowed me to come to your office the last time we spoke. And now for the first time, you visited us here at Planetary Society headquarters. Oh, your headquarters is absolutely beautiful. I really like your new digs. They're great. We like it too, but then we don't have, you know, mission control right down the hall

from the office here. So very exciting. Always wonderful to talk to you and thank you for doing this once again. I'll look forward to next time. Oh, I look forward to it too, Matt. Thanks. Linda Spilker, the project scientist

for the Cassini mission. Prior to that, the deputy project scientist. Prior to that, was also project scientist prior to that was also with the mission. She's been on the mission since she was about, oh, I think about eight or nine years old. Somebody who also has been at it for a long time, Bruce Betts, is going to join us in a moment for this week's What's Up. Time for What's Up on Planetary Radio. Here is Bruce Betts, the Director of Science and Technology for the Planetary Society. With a load of new stuff for us, I bet you're going to mention Venus.

I am. Dang it. So much for the surprise. I'm sure people are shocked. I've mentioned it every week for the last several weeks. It's the thing. It's the thing in the early evening that's shining super bright over there in the West. And so it's hard not to mention it when you talk about fun, easy things to see in the night sky. This is getting freaky. I mean, it's been so bright and so high in the sky for so long now. Yeah, it really doesn't require any complex or alien explanations. You'll be happy to know it all fits with the orbital path and such. All right, as long as it's following the rules.

It is, it is. And when you find Venus, which is super easy, look to its left, upper left, and you'll see Mars only 1 200th as bright as Venus right now. And then in the round 11 in the evening or so, Jupiter rises. And when Jupiter's up in the east and then the south in the pre-dawn, you can check out the bright star, though not nearly as bright as Jupiter, Spica, which is pretty darn close to it, below or to the lower right of it. And then we move on to this week in space history. Start with another look back since it was during this week that 2003, the Columbia disaster occurred. So we will remember those seven astronauts. Remember those seven astronauts.

And then on a much happier note, 1971, Apollo 14 both launched and landed humans on the moon. Yeah, a lot of memorial services taking place at NASA centers around the country this week, as is very appropriate. We move on to Random Space Facts. And there I had Linda Spilker in the studio. I could have had her do a nice intro for you, but no, no, we get to hear you again. No, it's just me. So Apollo 15, we talked about this, Matt. Apollo 15 left on the moon a small astronaut sculpture called Fallen Astronaut and a plaque with the names of the 14 astronauts and cosmonauts known

to have died up until that point. I was blown away by this when you showed me this image of these objects sitting on the moon. I had never heard of this. Yeah, I mean, it was kept pretty low-key. Dave Scott wanted it to be quite low-key, but it was put out there publicly, but I missed it for many years. But it's kind of nice. Yeah, very nice tribute. All right, we're ready for the contest. I asked you approximately how wide is the combined complex caldera, so volcanic collapse craters, of Olympus Mons, the largest volcano in the solar system. How did we do?

Turns out that caldera is big. It's huge. Like the whole volcano on Mars. Ron Brown of Florham Park, New Jersey has not won the contest in three and a half years, according to my records. He said combined complex caldera of Olympus Mons is 60 to 80 kilometers wide. Did he make it? He did indeed. It's huge. It's bigger than most volcanoes on Earth, or at least comparable, and it's just the caldera at the top. I got some other good comparisons. Samantha Glick in Minneapolis, she said the largest shield volcano on Earth is Mauna Loa, in Hawaii, of course, which has a caldera that's about 6.2 by 2.5 kilometers. So I don't know, you know, 4 by 1.5 miles. If placed end-to-end along the long

axis, you could fit almost 13 Mauna Loa caldera complexes inside the long axis of the Olympus Mons complex. Nice. This one's quite illustrative from Mark Wilson in San Diego. The Beverly Hills mansion of Bruce Betts would just barely fit inside. Darn, I was trying to keep that a secret. Mark Sulfridge, Boise, Idaho. This is pretty cool. It's literally too massive to appreciate visually if you were standing on the Martian surface near it, you would be unable to take the whole thing in. The curvature of the planet and the volcano itself would obscure your view.

Stunning. And it's, I don't know if anyone mentioned, it's over three kilometers deep, too. So 9,000, over 9,000 feet deep. Funny you should mention that, because Brian Mangold in Maricopa, Arizona did exactly that. He said, if you were standing up on the edge of the caldera, looking down those three kilometers, who could resist the urge to lean over and spit into it? So Brian, we want you to really think carefully about this before you take off your helmet. True. Very true. Also, it would be an interesting physics problem to figure out how quickly your spit freezes or sublimes.

Right. Would it even reach the bottom? Yeah. Or at least would it reach it as liquid? Probably not. Well, Ron Brown, you are going to get a Planetary Radio t-shirt, a Planetary Society rubber asteroid, and an itelescope.net account. A 200-point account worth a couple hundred dollars, American, to use

that worldwide network of telescopes. So congratulations, Ron. We're ready for the next one. Going back to the Apollo 15 plaque and statue, who created, who sculpted the fallen astronaut statue that Apollo 15 astronaut Dave Scott left on the moon with a plaque commemorating dead astronauts and cosmonauts? It's a whole weird story I got rather entranced learning about. Go to planetary.org slash radio contest. We're going all artsy on you this week.

Same prize package being given away, the one that you just heard about. You've got until Tuesday, February 7th at 8 a.m. Pacific time to get us this answer. All right, everybody, go out there, look up at the night sky, and think about what quote you would frame on your wall. Thank you, and good night. Inside of a dog, it's too dark to read. Groucho Marx, that would be the quote on my wall. He's Bruce Betts, the Director of Science and Technology

for the Planetary Society, who joins us every week here for What's Up. Oh, and is continuing his class at CSU Dominguez Hills. Yeah, go to planetary.org slash Betts class to watch the classes. Matt and I will be doing next week's What's Up segment during the class. It'll be exciting. You can actually be terrified by what we look like if you're interested. That'll be class two of the class. We're second class once again. Thanks, Bruce.

Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its brave members. Daniel Gunn is our associate producer. Josh Doyle composed our theme, which was arranged and performed by Peter Schlosser. I'm Matt Kaplan. Clear skies.