Planetary Radio: Space Exploration, Astronomy and Science - What's New at Saturn? Checking In With Cassini's Linda Spilker

Episode Date: May 7, 2007

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A Cassini-Saturn update from Lindus Filker, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. As so often happens in science, the Cassini spacecraft is uncovering new mysteries, even as it provides answers to old questions about Saturn, its rings and its many moons.

As we've done several times in the past, we'll turn to Deputy Project Scientist Linda Spilker at JPL for a quick review of what the big spacecraft has recently shown us about that ringed wonder a billion miles away.

We're also not far from a really interesting Q&A about all that ice at the Martian poles, delivered by Emily Lakdawalla. And Bruce Batts offers a remembrance of Wally Schirra in this week's What's Up. Bruce will also tell you where to look for Saturn and other planets while we give away another Planetary Radio t-shirt. Of course, the loss of Walter Wally Schirra is in our space headlines this week. Hard to believe it has been almost 45 years since he rode six times around the Earth in a tiny Mercury capsule.

My colleague Amir Alexander has posted a nice tribute to Shara at Planetary.org. Planetary Society Executive Director Lou Friedman said that WALL-E exemplified the spirit of optimism, achievement, and vision that dominated the early days of the space age. We miss that, and we'll miss him. Lots more on the news, including the discovery of a molten core deep inside Mercury, and lots of wonderful images from New Horizons' recent Jupiter flyby. It's all there at planetary.org. Time for Emily. I'll be right back with Linda Spilker.

Hi, I'm Emily Lakdawalla with questions and answers. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, Why does Mars have one water ice cap and one carbon dioxide ice cap? This question is based on slightly outdated information. Based on data from the Mariner and Viking missions, scientists once thought that Mars' north polar ice cap was made of water ice, while the southern one was made of carbon dioxide. However, the better views of Mars afforded by the recent fleet of spacecraft, beginning

with Mars Global Surveyor, have revealed that both the north and south polar caps are made almost entirely of water with a thin surface veneer of carbon dioxide. Why this double layer structure? Mars's surface water is all in the polar caps because water is not stable in either solid or liquid form at the surface near the equator at any time of year, but it always freezes at the poles. So when atmospheric circulation takes a water molecule to one of the poles,

the cold temperatures freeze it to the ground and keep it there for good. So where does the carbon dioxide ice come from? Stay tuned to Planetary Radio to find out. Linda Spilker has spent almost half her life on the Cassini-Huygens mission team. She would tell you it has been time very well spent. She serves as co-investigator for Cassini's composite infrared spectrometer, but has much broader responsibility as the mission's deputy project scientist. We like to check in with her now and then for an overview of the science returned by the bus-sized spacecraft, even though we've focused on specific discoveries in other shows.

I recently got her on the phone in her Jet Propulsion Lab office. Linda, it's so good to talk with you again. Welcome back. It's wonderful to be back. Where shall we start this time around? Well, maybe a good place would be to start with is Titan. Titan is always surprising us. You'd think that after being almost three years in orbit about Saturn, we'd have it figured out, but we don't.

And Titan is still surprising us. And I think one of the most interesting things that has happened in the last year is that the lakes that we first saw on Titan have now grown into seas, that the high northern latitudes of Titan appear to be dotted with lakes and seas, and some of these seas are larger than the Great Lakes on Earth and perhaps even as large as the Caspian Sea. And they look very dark in our radar images, look like very dark features. We've also now seen hints of them in the images as well.

And the possibility exists that these might be lakes or seas filled with liquid methane or ethane combination. And the visual and infrared mapping spectrometer is trying to zero in and give us some composition information on these dark features and see if we can confirm once and for all that they're filled with liquid. So very exciting. This very interesting moon that's shrouded in this sort of smog-like haze, we're sort of peeling back that haze and getting a better look at the surface and the processes going on there.

As I've mentioned before, Titan is remarkably Earth-like. It has river channels, it has sand dunes, you know, mountains, evidence of a few craters, but just remarkably Earth-like in its appearance of its surface. I hope that everybody listening to this show has seen some of these radar images that look photographic, of course. show has seen some of these radar images that look photographic, of course. And I know that what you're finding now, I guess it's not that great a surprise, but you would hope to see some of this from the Huygens probe, right, as it descended and instead only got kind of indirect evidence. Right. We were at much lower latitudes with the Huygens probe. And we think now that the

liquid is probably concentrated at the poles, although there may be some liquid underneath the sand dunes, and maybe it's a seasonal effect. One of the things we'd really like to see is, as the Cassini mission goes on, does the liquid migrate from the northern dark, what's in the dark now, into the southern regions as the seasons change on Titan? And then to get a closer look at the South Pole and see if there might be, you know, perhaps lakes tucked away at the South Pole as well.

You mentioned that the topography that we see on Titan, it seems to be, it seems so Earth-like. I mean, to me it looks like Mars except with liquid on the surface. It is astonishing just how Earth-like it looks like Mars except with liquid on the surface. It is astonishing just how Earth-like it looks. Here's this place that's so far from the sun that the sun is going to start to look like a large star, and yet you have now methane playing the role of water on Titan, and so you get the same kinds of processes of methane rain, perhaps even icy particles of methane that come down.

Then methane flows on the surface and evaporates and the cycle starts over again. Now, while Europa and even Enceladus, as we heard recently on a planetary radio program, are getting more attention, the usual attention, I should say, regarding the possibilities of life, I've even heard Titan mentioned, and I was surprised by that because it's still awfully cold and the water is hard as rock, quite literally. Right, right. The question is whether or not there might be what they would call cryovolcanoes,

water volcanoes, which would bring up liquid periodically to the surface. And if that's the case, then you need a source of warmth underneath that rock-hard icy surface to have that liquid water. We know that some process is putting methane into the atmosphere of Titan. It has to be replenished because it gets used up. It goes to the upper atmosphere, gets disassociated, and so we need to have some supply of methane. Maybe it comes up with these, you know, if there are cryovolcanoes that are active on Titan, maybe this is one way to bring the methane to the surface. And you can bet with Cassini we're looking very carefully for any sign of change on Titan's

surface, and we'll continue to do so as we have the continuing flybys of Titan. Let's move on to a special event that took place last September, which we really haven't talked much about on this show, but it sure led to some great science. Oh, it was just a remarkable opportunity. It was a time when the sun was hidden by Saturn, and Cassini was at its most distant point in its orbit, and so we actually had two whole days with the Sun hidden

behind Saturn to image the rings and Saturn and really get a good look at the Saturn system and with the Sun behind Saturn that's a great time to really look for dusty rings in particular if you've ever had a dusty windshield and you drive into the afternoon Sun you'll you'll know that the dust on your windshield brightens up. And in the same way, any tiny, dusty ice particle material in Saturn's system brightens up. And lo and behold, when we took our images and got them back, we discovered that Saturn now has two new rings, two faint, dusty rings.

One of those is associated with a pair of co-orbiting satellites, Janus and Epimetheus, and the second is associated with a moon that Cassini discovered called Pallene. These are tiny little moons and perhaps impacts from micrometeoroids, you know, run into them and sort of poof the dust off and create then a dusty ring that's in the same orbit as these tiny moons. create then a dusty ring that's in the same orbit as these tiny moons. Or maybe sometimes, maybe there are bigger particles we can't quite see. They bump into each other. Maybe they could create bright, dusty features.

We saw a couple of new dusty rings in the Cassini division as well. That's the big gap between the A ring and the B ring. And they weren't there in the Voyager images, and now here we see them with Cassini data. Speaking of these little moons that are associated with the rings, we're getting more and more confirmation that they're pretty critical to, what, keeping these rings herded? Yes, they can keep the rings in place. A great example is Saturn's F ring, which has a pair of moons, Pandora and Prometheus, on either side, that interact with that ring in a very complex and fascinating way.

Tiny Moon Atlas, we think, might be helping confine the outer edge of the A-ring. That's the outermost of the main rings of Saturn. And it's kind of fascinating. It seems like now wherever you find a tiny moon, you know to look for a ring. Or if you see a ring, conversely, then you know to look for a tiny moon. Pandora and Prometheus, are they, I don't really remember, but are they the two that do this little dance in their orbits? That's Janus and a Prometheus. They actually switch orbits periodically,

and Cassini has watched that once, and we hope to watch it again in 2009. So the ring study is certainly not over either, right? Oh, no. Oh, no. In fact, in the last several months, we've gotten incredible views of the rings. Cassini climbed higher and higher using Titan to change its orbit, and we actually got up to about 50 degrees inclination. And they're just these stunning views.

If you look at the website, some of the pictures of the rings, you know, almost fully open around the disk of Saturn, and, you know, just very beautiful views of the rings. And we're going to continue. Toward the end of the mission, we get up to even higher inclination, 70 degrees, and we'll be looking down at the rings and at the poles of Saturn. So very interesting times to come. We'll continue our conversation with Linda Spilker of the Cassini mission in a minute.

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The Planetary Society, exploring new worlds. Welcome back to Planetary Radio, where we're in the middle of a Cassini update from the mission's Deputy Project Scientist, Linda Spilker. We've already heard about Titan, other moons, and those magnificent rings. How about Saturn itself? Let's go on down to the planet

and talk about what you're finding at the northern and southern tips of this big world. Yes, very interesting. At the poles of Saturn, it's quite different. At the North Pole, which is in the dark right now, we just recently discovered that there's a six-sided hexagonal feature, kind of looks like part of a honeycomb, that covers the entire North Pole of Saturn. It kind of looks like part of a honeycomb that covers the entire North Pole of Saturn. And we had seen this in the Voyager 1 and 2 images in the early 1980s. With Cassini, we're now seeing it again.

So it's lasted, you know, for a long time, over 25 years. We're seeing that it sort of appears to be synced up with the rotation of Saturn. Right now, the North Pole is in a dark, long polar night, lasts about 15 years. And so we were looking in the infrared at the five micron window, which is much redder than the eye can see, but we can see the heat coming out from Saturn and use that to discover the hexagon shape. Any idea what's forming this geometric shape? I mean, is it a storm? That's a really good question. We think it has a lot of similarities to the Earth's polar vortex. Only there the winds are blowing in a circular pattern.

And at Saturn, we seem to get a hexagon rather than a circle. And this hexagon is huge. You could put almost four Earths across it. And so we're going to be looking at it more carefully in the future and trying to puzzle out what is creating these basically straight sides, almost perfectly straight sides of this hexagon. And then at the other pole, at the south pole, the one that's in the sunlight, there appears to be a huge hurricane-like storm.

You know, it has an eye wall, you know, towering clouds, and then a sinking center, and it's very reminiscent of a hurricane, only there are no oceans of water underneath to drive it like you would drive a hurricane on the Earth. So we're puzzling about the South Pole as well as the North Pole. Do we have less of a history with the South Pole and the storm there? Do we have any idea how long it has been there? Yeah, I'm not sure of exactly how long it's been seen. It's much smaller. It's only about, I think, two-thirds, about 5,000 miles

across, two-thirds the diameter of the Earth. So it's much smaller. And again, we see it most clearly in the visual and infrared with a visual and infrared mapping spectrometer at this 5 micron window. Again, we also in the far infrared with the composite infrared spectrometer, we've seen that the center is warmer, much like in the eye of a hurricane. As the winds are going down, the eye is actually warmer, and we've been able to measure. It's about 4 degrees Fahrenheit warmer at the center of that eye of the hurricane. Back to that hexagon up north.

Has anybody come up with any kind of mathematical model yet? Are they even close to figuring out how such an odd shape could be formed? Well, they're trying to look at fluid dynamics, and I've seen some lab work that they've done where they try and set up a series of six little vortices and see if that could then generate that shape. And then the question is, how long is that shape going to be stable? So as the seasons change and the sunlight goes up to the South Pole, we'll see if there are any changes with this hexagon. What's very interesting is that the rotation of the hexagon

appears to be linked to the rotation of Saturn's deep atmosphere, and maybe even to the rotation of Saturn itself, because that's a big puzzle. We still don't have a good rotation rate for the interior of Saturn. Yeah, and regular listeners know that Emily Lactuala actually tried to address this in one of her more fascinating Q&As. It's a really tough thing to tell how fast that ball is spinning. That's right.

That's right. Since you have nothing but clouds, there's no solid surface that you could use to see how fast it rotates. And the method we used for Jupiter, Uranus, and Neptune to measure the radio signal, we're finding out that that signal gets actually slowed down by the geysers and the material coming out from Enceladus actually slows down this apparent rotation rate. We think that's why there's a six-minute difference between Voyager and Cassini, that we got a rotation period that was six minutes longer, which just amazed everyone.

And now we know what we're seeing is the rotation rate of the plasma around the planet, not of the planet itself. So it's still an open question. What's Saturn's rotation rate? Saturn, like the rest of the solar system, continues to amaze us. You surprised me when you reminded me that we're headed into the last year of the main mission, the primary mission of this spacecraft. That's right.

That's right. We have one year left. The prime mission ends on July 1st of 2008. We have a lot more coming up. In fact, there's 15 more close flybys of Titan. And in May alone, we have two more close flybys. Then two close satellite flybys in September of 2007. We have a close flyby of the moon Iapetus. And this time, we're going to get a good look at its bright side.

It's sort of this moon with both a dark side and a bright side. So this time around we're going to get a good look at the bright side. We'll find out, does that mountain range that appears to go around the equator, does it go all the way around? We'll get a close look at the bright side. And then we get another close look at Enceladus in March of 2008, and that will be our last close flyby of Enceladus in the prime mission. Catch another one of those volcanoes or cryo.

Yeah, see some of the geysers going off and see if we can learn more information about how that process works on such a tiny, tiny moon. You know, I get the weekly updates on the mission, and every one of them starts with, the spacecraft is in excellent health. It's very hard to believe that NASA and the public would want to see this spacecraft just put to sleep in not much more than a year from now. Oh, certainly not. In fact, what we're planning is, we're planning for a two-year extended mission, and that mission would be filled with a lot more Titan flybys. We have a plan that could include seven more Enceladus flybys and all sorts of great views of the rings.

In fact, it's a very interesting time. The sun will actually be transitioning from the south side to the north side of the rings, what we call an equinox. So we want to try and look. And so we have this plan before NASA, and we're just waiting to hear back if we're going to be able to go ahead with that two-year extended mission. My fingers are crossed, and I don't think you'll need a lot of luck to get that. At least I hope you won't. Remind me, how many years have you been working on this mission? Oh, I started on Cassini back in 1986, or 85 actually, before it even had a name

and before it was just sort of a dream in people's imaginations. And it's just been wonderful to see that dream evolve into the mission and be part of getting to Saturn and helping look at the data and just sort of sitting back in awe and wonder at the discoveries Cassini's making. 22 years and hopefully no end in sight. Yes, yes, that would be great as long as the spacecraft is healthy and NASA is willing to put forward the funds, hopefully Cassini will remain in orbit and taking data. Lots more science to do in the Saturnian system. Linda, thank you again very much and we will absolutely come back for another update, even though I'm sure we will continue to pay attention

to specific parts of what Cassini is discovering out there, even before we have you back for an update. But we'll also let folks know, remind them once again, that they can check out the official Cassini website and the Planetary Society's excellent site that keeps track of Saturn and the Cassini- and the Planetary Society's excellent site that keeps track of Saturn and the Cassini-Huygens mission with the links that are probably very close to where you may be listening to this radio show at planetary.org. Linda, take care and we'll talk again soon.

Thank you very much, Matt. It was a pleasure to be here. Linda Spilker is the Cassini Deputy Project Scientist. She's also the co-investigator for the Composite Infrared Spectrometer on that mission and a principal scientist for the Jet Propulsion Laboratory near Pasadena. We'll be right back with this week's edition of You Know Who, Bruce Betts with What's Up. That'll be after a return visit by Emily. I'm Emily Lakdawalla, back with Q&A. Mars's polar caps both consist of water ice with a surface coating of carbon dioxide.

Carbon dioxide is the major constituent of Mars's atmosphere. Over most of Mars, for most of the year, carbon dioxide exists only as a gas. But at the poles, during the long, dark winter, it gets cold enough for the carbon dioxide to freeze to the surface. The carbon dioxide frost hugely expands the apparent area of the polar cap. In fact, the seasonal carbon dioxide cap on Mars can contain more than a quarter of Mars's entire atmosphere. So when it's winter at one of the poles, the atmospheric pressure drops across the entire planet by as much as 25 percent. In spring, when sunlight comes to the pole again, the carbon dioxide sublimates, thickening the atmosphere and shrinking the cap. That thicker atmosphere is more capable of carrying dust, which is why the dust storm season begins toward the end of spring in Mars' southern hemisphere. But as spring comes to the South Pole, autumn comes to the North, and soon that seasonal high in atmospheric pressure reverses again. The carbon dioxide that spent the southern winter at the South Pole

migrates to the North Pole for another frigid season, experiencing two winters for every Martian year. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Time for What's Up on Planetary Radio. Bruce Betts, the director of projects for the Planetary Society, joins us once again. Tell us about the night sky and do some trivia and maybe a random space fact or two.

Hi, welcome back. Hi. How are you doing, man? I'm okay. How are you? Actually, I have a cold. I know. I'm worried about that.

I'm sitting as far away from you across the table as I can, which is no further than usual. Yes. Could you stop breathing, please? Okay. The show I've always dreamed of. Now breathe. Breathe. Okay.

Thank you. You're worrying me. All right. Venus. Venus. Check out Venus in the early evening sky over there in the west, looking really, really bright. We've also got the moon passing through by the planets, as seen from Earth, for the second half of this month.

So on the 19th, the moon is right near Venus, and you will see it on the 22nd, right near Saturn. Saturn can be tricky to find if you don't know what you're looking for. So the somewhat bright star-like object near the moon on the 22nd, or even on the 21st, it's on the other side, will be Saturn. And at the very end of the month, Jupiter, playing with Jupiter. So we've got Saturn up in the early evening, getting farther and farther down in the west in the early evening. As time goes along, it'll snuggle up to Venus in a little while.

And we've got Jupiter rising in the late evening and up in the pre-dawn, high in the sky, and Mars over there looking dim still in the east, east-southeast, right before dawn. Thank you, Dory Swell. Let us go on to this week in space history. In 2003, four years ago, Hayabusa launched off an asteroid, sampled an asteroid, and they've just recently fired up its one remaining thruster and its one remaining gyro and are trying to limp it home by 2010. In any case, it's still a stunning mission, first sampling of an asteroid and great up-close and personal data, and we'll hope for it.

Hey, and 40 years ago, 1967, the M2F2 flying body, NASA's flying body. Yeah, lifting body. Crash, lifting body, thank you. And, of course, the significance and pop culture of that is? What? It was used in the opening credits of The Six Million Dollar Man. Oh, that's right. She's breaking up.

She's breaking up. We can rebuild him. We have the technology. Better, faster, stronger. The actual pilot came out reasonably unscathed. He actually did lose an eye due to a post-accident infection. But considering the gnarliness of the crash, pretty amazing. Red Rose, first flight!

I'm going to bring this down again, but in an up kind of a way. Astronaut Wally Schirra was the only man who flew in all three of America's first human space programs, Mercury, Gemini, and Apollo. Of course, recently passed away. Yeah. And so I thought I'd note that, kind of a neat piece of trivia there. Such a great character. Such a terrific guy.

And, you know, went on to have a little bit of a career on camera next to Walter Cronkite, covering Apollo and other missions. And, of course, what I remember him and his Apollo 7 colleagues for were the little signs they held up, the little joke signs that were pretty funny. Paul Haney, are you a turtle? So I miss him. Sorry to say he's gone. No, he is.

Known for a sense of humor, not that we could appreciate that. On to the trivia contest. We asked you to name two astronauts or cosmonauts, the ones who have the most accumulated time spacewalking. In other words, in other words, in EVA, extravehicular activity, how'd we do? We did well, except that there was a good deal of division this time because apparently a lot of the references that list this kind of information are out of date.

Everybody agreed that the number one, the record is held, in fact, by Anatoly Solovyov. I think I got that right. He's the clear winner with 77 hours and 41 minutes and 16 EVAs. But a lot of people then said it was this fellow Ross, an American astronaut. Not so. Not so. And apparently this has all happened pretty recently. It turns out that it's Michael Lopez-Alegria with 67 hours and 40 minutes who took number two for most time spent floating around in a spacesuit. Outside your comfortable spacecraft.

Yeah. And by the way, it was Margaret Schwartz. Congratulations. Who got the luck of the draw this time. Margaret Schwartz from Baltimore, Maryland, who indeed came up with Anatoly and Michael. And for that, Margaret gets a Planetary Radio t-shirt that we'll put in the mail real soon. Thank you, Margaret. And if you'd like to take your shot at winning a Planetary Radio t-shirt, answer the following question. We turn our attention to near-Earth objects.

How many near-Earth objects have been discovered? We'll just take it pretty roughly. I'll give you to the nearest hundred, or to within a hundred as of the airing of this show. We'll put you into the pot for the random selection to win the prize. Yeah. So go to

planetary.org slash radio, find out how to enter. When do they need to get those entries in by, Matt? They should toss their rock into the hat by November. Not November. What am I talking about? You've got plenty of time. No, May 14. Monday, 2 p.m., May 14.

All right, everyone. Go out there, look out at the night sky, and think about all the colors in white. Thank you, and good night. He's Bruce Betts, the director of Projects for the Planetary Society, here with us every week in full living color for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week, everyone. Thank you.