Planetary Radio: Space Exploration, Astronomy and Science - A Saturn Update from Cassini's Linda Spilker

Episode Date: March 28, 2005

A Saturn Update from Cassini's Linda SpilkerLearn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Join us for a progress report from Saturn on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. What's a billion miles away, working perfectly, and offering up almost daily surprises about a giant ringed planet? It's the Cassini spacecraft, of course, and Deputy Project Scientist Linda Spilker will give us an update in a couple of minutes. Who's the highest human of them all?

We'll find out from Bruce Betts in today's What's Up Space Trivia Contest. It all begins with these space headlines. Dust devils, nothing to get excited about, right? Unless they're on Mars. Cameras on the Mars Exploration Rover Spirit caught two of the little demons for the first time. You can see them and get an update on both rovers at planetary.org. Cosmos 1, the first solar sail, is getting closer to launch. Eight huge triangular blades have been carefully folded and attached to the spacecraft's body. We'll be bringing you much more coverage of the light-driven vehicle in the coming weeks, with liftoff planned for sometime between April 20 and May 30. And NASA has announced the first of its Centennial Challenge competitions.

A total of $400,000 will be presented to teams that develop very strong yet lightweight tethers for use in space and for advancements in the wireless transmission of electricity. The idea is to follow in the footsteps of the XPRIZE and earlier aviation competitions to encourage new technologies. Now, if only they had one for Best Space Radio Show. You are one minute away from a visit with Cassini's Linda Spilker. In the meantime, Emily has a Q&A ripped from the headlines, and she's reading it by the light of an extrasolar

planet. I'll be right back. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, I heard that astronomers have detected light from an extrasolar planet by watching when the planet disappeared behind its star. But how can you see light from a planet when it's behind a star? This is the first time that human observers have ever directly seen the light from a planet outside our solar system. It's incredibly difficult to see that light because planets are such faint light sources compared to the stars that they orbit. Through human eyes, the stars are 10,000 times brighter than the planets. But two different teams of scientists reported this week

that they have managed to detect the light from two previously discovered extrasolar planets. To do so, they used infrared detectors aboard the Spitzer Space Telescope, a brother mission to Hubble. Infrared wavelengths are useful to planet hunters because typical sun-like stars are much dimmer in the infrared than they are in visible wavelengths, only 400 times brighter than their planets. Even with this advantage, the scientists couldn't detect the light from the planets until the planets had passed behind their stars. Why not? Stay tuned to Planetary Radio to find out.

Radio to find out. Linda Spilker, thanks very much for taking time to join us on Planetary Radio. What's the latest from Cassini? Well, one of Cassini's new and exciting discoveries is that Titan is no longer the only moon in the Saturn system with an atmosphere. It looks like one of the other moons, Enceladus, also has an atmosphere, albeit, I think, a very tenuous one. It turns out that during the two close flybys we've had recently, the magnetometer experiment measured what we call a draping, or the magnetic field lines bent around Enceladus.

And they also saw a kind of wave, a plasma kind of wave, in which they detected ionization of water molecules coming up from the surface of Enceladus. So by some process, we don't understand yet, it looks like material is coming up from Enceladus. And that's quite interesting because we know that Enceladus is the source of the E ring, this diffuse, broad ring spreading through a large part of the Saturn system. And so now we're very curious, how are those particles getting off the surface of Enceladus geysers or volcanoes like we have on Io and on Triton, or through some other process we haven't even imagined yet. So Cassini continues to reveal all kinds of wonderful surprises. Oh, it absolutely does. It's sort of like reading a mystery story, and you have all of these clues, like on Enceladus, all of these clues,

but haven't quite put all of the pieces together yet to find the prime suspect, in this case, creating the atmosphere on Enceladus. And then the question, do the other moons, some of them perhaps, have atmospheres similar to Enceladus, and maybe they in some way are also contributing to Saturn's E-ring? I didn't realize until I started to research to prepare for our conversation that Cassini is really at least five missions in one, and maybe more than that, maybe five categories of missions, because you've got what? You've got the planet, you've got the rings, you've got the icy moons, you've got weird old Titan, and you've got the magnetosphere.

That's right. You have each of these areas for study and that's one of the challenges i have with my job is sort of balancing the science in each of these areas working with scientists both in the united states and in europe to sort of maximize the science return from the mission within constraints like the schedule and the budget and and just working with everyone within the project. So it's quite a challenge. Cassini doesn't have a scan platform, unlike Voyager and Galileo. So we have to turn the entire spacecraft every time we want to point to a target.

And so, as you can imagine, we have to learn how to share, how to take turns when we use the spacecraft. Scientists have to learn how to share. That's right. That's right. Well, you're a mom. You must have had some experience with that, with multiple children that you raised. A lot of your job, apparently, is arbitration. That's absolutely right.

It's sitting everyone down together and then trying to get, if you can, consensus or get agreement for the best plan. In fact, the way we designed the tour initially is we took each orbit that Cassini would have around Saturn, there's about 75 of those, and divided it up into pieces that would have a particular focus, a focus perhaps on Titan or on the planet itself or the rings, the icy moons, or the magnetosphere.

And then within those segments, we asked separate little teams to come up with the best plans that they could for the observations within those segments, we asked separate little teams to come up with the best plans that they could for the observations within those segments of the tour. When you have a conflict, and I guess it happens now and then, where you've got one team of scientists with their instrument, and they're telling you, we absolutely have to get this observation during this pass or during this orbit. And you've got another group saying the same thing. What happens? Well, first we try and get the two teams to agree.

We try and get them to sit down and see if they can work out a plan, a win-win plan where each side gets a little bit of what they want. And if they can't, then it goes up through the project to the project scientist who finally listens to the arguments on both sides and then has to make a decision. And we've just had a very few of those where it's had to come down to a very tough choice. It's either A or B, but we couldn't do both. In a lot of cases, we find a way to compromise and get a little bit of each flavor of science. And that's when you mentioned the project scientist.

That's your boss, right, Dennis Manson? That's correct. That's correct. So you guys are a team, and while your title, you are project scientists, you do much more than science. There's a lot of administration involved here. Right, right. In organizing and running meetings, we have project science group meetings three times a year. Have to organize and coordinate those and also any of the other science-type discussions that come up. Right now we meet once a week on a telecon with the scientists,

and they phone in and we have discussions and talk about publications, upcoming meetings, new science results, and encourage collaboration in that way too. Now at the same time, you are a scientist, and you are involved with at least one of the instruments on Cassini. That's right. I'm a co-investigator with the Composite Infrared Spectrometer, and my role there is to organize the ring observations that we can make in the far infrared, measuring the temperatures and learning about the composition of the molecules that make up the rings themselves. It's very, very fascinating, again, trying to solve this

mystery of the rings. How old are the rings? They appear to be very young. What are the rings made of besides water ice? What processes go on the interaction between tiny moons that orbit just outside the rings and the ring particles themselves creating these beautiful structures called spiral density waves? Now, are these the tiny moons you mentioned? Are these the so-called shepherd moons? Right. There's a number of very tiny moons that orbit just outside the edge of the A-ring, Saturn's main ring, of Saturn's main rings. And these moons interact with the ring particles themselves at different places, creating structure in the rings. The two shepherding moons around either side of the F-ring are very interesting. One of them, Prometheus, has actually been seen stealing material away from the narrow F-ring. Prometheus has actually been seen stealing material away from the narrow F ring.

You know, you could see these stream of particles actually going toward Prometheus and being pulled away from the F ring. Wow. So this is just one thing that we've learned about the rings of Saturn. What are we discovering about the planet itself? What has Cassini revealed? Well, we've seen some interesting evidence that we've measured some lightning coming from Saturn. And I've actually, with the cameras and the radio and plasma wave spectrometer, Well, we've seen some interesting evidence that we've measured some lightning coming from Saturn. And I've actually, with the cameras and the radio and plasma wave spectrometer, been able to pin down the location of what looks like the equivalent of a thunderstorm or a giant storm on Saturn itself with the lightning coming from it. So that's very exciting.

Is this a persistent storm like the ones we know so well on Jupiter? These appear to be quite different. We're approaching, we're at Saturn now, what would be southern summer. And if you've seen some of the pictures on our website, you notice that the shadow of the rings is going up over a good part of the northern hemisphere. And we think that this shading that's going on might play a role in creating these episodic or periodic thunderstorms that we see on the planet itself. I was on the website last night, and there are some wonderful shots of Saturn with the

shadow of the rings across it. It really is a beautiful place. Right. In fact, there's one picture in color. It's like a Kodak moment shot. It shows the tiny moon Mimas, and the rings are in the bottom of the picture, and you can see the shadow of the rings slanting out across the planet. It's just a beautiful picture.

We have a lot more to talk about, and this is just a progress report on a mission that we hope has many years yet to run. But we do need to take a break. When we come back, let's talk about some of the other recent results revealed by Cassini and, of course, by Huygens. We've got to talk about Titan. So we'll do that when we return with Linda Spilker, the Deputy Project Scientist for the Cassini mission from JPL.

This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary Society, the world's largest space interest group. The Planetary Society is helping to explore Mars. We're tracking near-Earth asteroids and comets. We sponsor the search for life on other

worlds, and we're building the first ever solar sail. You can learn about these adventures and exciting new discoveries from space exploration in the Planetary Report. The Planetary Report is the Society's full-color magazine. It's just one of many member benefits.

You can learn more by calling 1-877-PLANETS. That's toll-free, 1-877-752-6387. And you can catch up on space exploration news and developments at our exciting and informative website, planetarysociety.org. The Planetary Society, exploring new worlds. We're back with Planetary Radio, and our special guest at JPL is the Deputy Project Scientist for the Cassini mission, Dr. Linda Spilker. Linda, we said we wanted to talk about some of the other things we're learning from Cassini, but of course, there's also Huygens. And I guess there was a major presentation just a few days ago.

Huygens had an interesting and kind of rough ride down to the surface of that little moon. That's right, Matt. We had some reports from the Huygens probe scientists at the Lunar and Planetary Science Conference. And it looks like after the main chute opened, it was a pretty rough ride, that the probe was swinging back and forth, tilted quite a bit. And actually, it started spinning in one direction and ended up stopping and spinning in the opposite direction as it was going down. And then as the atmosphere got thicker, we went to a smaller parachute. And as we got lower down in the atmosphere, the ride seemed to be smoother and even out. And when you think about Titan, it's amazing. You can imagine looking at the

Earth from space and thinking about what the surface might be like, but only having pictures from space. And that's where we were with Cassini before the Huygens probe. And then imagine riding on the probe and getting a bird's eye view as you settle underneath the parachute closer and closer to the surface until you finally see actual rocks and tiny boulders on the surface of Titan. And it was just amazing. We landed with a sort of a gentle crunch on the surface. Some analogies for the surface of Titan are kind of like creme brulee. There's some kind of maybe a crust or maybe that penetrator landed, touched first on one of those icy rocks and then went through to the surface that appeared to be kind of like wet sand or maybe even like clay,

but much softer than that initial little piece of the surface. I said a little moon. This is anything but a little moon. There's an awful lot of moon for us to explore up there. That's true. In fact, Titan is bigger than the planet Mercury. And if Titan had formed anywhere else in the solar system, it would be a planet in its own right. So it is a large place with a large extended atmosphere. And that atmosphere is very much like the Earth's

atmosphere. It has nitrogen and it actually has some methane in it, but no oxygen. No, I'm still wearing my, very proudly, my Surf Titan t-shirt. But so far, we haven't found those liquid methane seas and rivers and lakes. Right. I wore my Surf Titan t-shirt the night of the Huygens landing, you know, just in case. But so far, it looks like we haven't found broad oceans or large lakes of liquid methane. And that's what we were expecting, given that the methane has been raining out onto the surface for a long time. We expected large pools or lakes of methane, and so far they just don't seem to be there. There is methane, though, I know, because when Huygens came down and warmed the surface a little bit, you started detecting some coming up

from the surface, right? That's correct, Matt. It turns out that the warmth of the Huygens probe on the surface warmed it up enough so that methane gas came out, and we had an instrument that could measure that gas coming out. And what's so amazing about Titan, it's minus 290 degrees Fahrenheit. It's colder than I can even imagine, and yet we have a liquid flowing on the surface. That liquid is methane.

And it works in the same way as water does on Earth. It actually creates drainage channels and stream beds and dry lake beds and sculpts the surface of Titan. So in many ways, Titan is very Earth-like in the processes of erosion that are going on on the surface. It's just amazing to see. I'm glad you mentioned how Earth-like it appears to be, because I guess we're now also seeing evidence of other Earth-like geological forces, including tectonics.

Right. There are evidence for tectonics or fracturing of the surface, evidence for volcanoes, a very special kind called a cryovolcano or cryovolcanism. Which we talked about on this show two weeks ago. Where you have water ice flowing instead of lava. There's some evidence of a few impact craters that are present on the surface as well. So in many ways, Titan's surface is very Earth-like. I guess there's still a lot of suspicion. I won't use the word hope because you're a scientist. But about the South Pole, because there seems to be a lot of weather going on there,

and maybe that's where some of this methane is pooling? Yes, it's southern summer on Titan right now. so the South Pole is one of the warmest places. And that's a place we've also seen clouds forming. And we think that maybe with the clouds comes methane rain. And we haven't seen anything that we can definitively say is a lake or an ocean. But that would certainly be a good place to look, a place where it's summer on Titan. How much more are we going to see of Titan as Cassini continues to make these close passes? I read that so far we've mapped or photographed about 30 percent. Are we going to see most of this moon eventually?

Yes, with the cameras and with the spectrometers, we'll very easily see all of Titan. We have a total of 45 close passes to Titan. We've only had a handful so far, so we have very, very many more. We also have an instrument, a radar instrument, can probe through the clouds to the surface. And we plan over the course of the mission to map out about 20% of the surface with the high resolution radar. What are you most excited about? What are you looking forward to, we'll say in the fairly near term, like the next six months to a year? Well, in the next six months or so, we'll actually be going into a period of orbits where we raise the inclination up slightly. And we do this to get a series of radio occultations of the rings and of the planet. And as a ring scientist, I'm

really looking forward to probing the rings with the radio signal. We have three different frequencies that we can probe the rings and to get a detailed look at what the structure of the rings is like. And we should explain briefly, when you say radio occultation, this is using the signals coming to or from Cassini because they will have to pass through the ring material or through Saturn's atmosphere. You'll be able to learn a lot about the nature of those. That's right. In fact, you can imagine if you were riding on the atmosphere, you'll be able to learn a lot about the nature of those. That's right. In fact, you can imagine if you were riding on the spacecraft, you would watch as the Earth went first behind the rings and then behind Saturn. And all the while, Cassini is sending a radio signal back to the stations on the Earth. And so they're picking

up how much that signal is absorbed by the ring particles or by the atmosphere. We call it attenuated. And from that, and also from some phase information in the radio signal itself, we get information about the structure of the rings and the structure of the atmosphere. We also have some close flybys coming up, one of Dione and one of Rhea, what we call targeted flybys. And so we'll get some good close looks at those icy moons, although that's a little bit later in the year. A lot of work going on out there, a billion miles away.

Is the spacecraft in good health? Are we looking forward to, fingers crossed, a long life at Saturn? Yes, so far the spacecraft has been in great health. A lot of the main systems, the main computers and so on, we have two of those. They're redundant, and so far we're, with the exception of switching out one reaction wheel, we're on all of the primary systems and haven't had to go to backup. So yes, the spacecraft health is looking good. And we hope for certainly the four-year prime mission and perhaps several years after that. You have already put in 17 years on this mission. You've been at JPL. You came here

right out of college and were lucky enough to dive into the Voyager mission. That's quite a continuity of experience that you've had with the outer planets. Right. I feel like an outer planet explorer. I've had a chance first with Voyager to be part of the Grand Tour and get close-up looks at four of the planets, Jupiter, Saturn, Uranus, and Neptune. And then as a ring scientist to go back to my favorite planet, to go back to Saturn and have a chance to study that system, and in particular that ring system. So is this your life for the foreseeable future?

Yes, yes. I'm working on Cassini and also looking ahead a little bit. I'm part of a project to look at what NASA might want to do next with regards to the outer planets, and I'm part of a Neptune study to look at what it would take to send a mission to go back, orbit Neptune in much the same way that we're doing now with Cassini around Saturn. And you'd like us to get out to that big blue-green place? Oh, I'd love it. It has an active moon Triton with geysers. It has an intriguing ring system complete with what we call ring arcs.

And so, yes, I'd like to go back. I think Voyager gave us a taste of what's out there, and now we need a mission to go back and really focus on the Neptune system and see what's there. Linda, this won't be the last time we talk. I'm sure there are going to be many more surprises and probably many more mysteries that Cassini will make us aware of that we never had any suspicion of, and I guess that's part of the fun. Oh, absolutely. Not knowing from day to day exactly what you're going to see and being willing to be surprised.

Linda Spilker has been our guest. She is the Deputy Project Scientist for the Cassini mission, has been with that mission for 17 years here at JPL. And I'll be back with Bruce Batts and this week's edition of What's Up right after this from Emily. I'm Emily Lakdawalla back with Q&A. In order to detect for the first time the faint light from two extrasolar planets, scientists had to watch those planets disappear behind their stars. When we stare at a planet from so far away, we don't have telescopes that are able to resolve the planet and separate its light from its stars. The light that we see represents the sum of the light from the star and the light from

the planet. But if the planet disappears behind its star, then all we see on Earth is the light from the star itself. To detect light from extrasolar planets, astronomers measured the light from the star itself. To detect light from extrasolar planets, astronomers measured the light from the sun and planet together, and then measured the light from the star alone, and subtracted the lone star light from the star and planet light. This leftover light represents the first faint glow ever detected from extrasolar planets. That light has already told scientists about the temperature and reflectivity

of these distant worlds, and someday that light will tell us what the planets are made of. 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, and so we are joined by Dr. Bruce Betts, the Director of Projects for the Planetary Society. Welcome back. Thank you very much. Good to be back, Matt. Good stuff up in the sky? Good stuff. We've got planets and a solar eclipse coming, so go out there looking for planets.

You can go in the evening. We've got Jupiter rising right around sunset. And it is coming up in the east. It is at opposition on April 3rd, meaning it's on the exact opposite side from the earth relative to the sun. And therefore, it is rising around sunset and setting around sunrise coming up in the east. Anytime in the early evening, the brightest star-like object up there is Jupiter. If you've got binoculars or a small telescope, take a look. evening, the brightest star-like object up there is Jupiter. If you've got binoculars or a small telescope, take a look and you can see little dots out to each side that will be four of Jupiter's large moons, the Galilean satellites. You can also see Saturn in the early evening. If you look in the south, up high after sunset, near Castor and Pollux, the Gemini stars, and it's looking kind

of yellowish. Also great through a small telescope, rings are very open right now and ready for you to look at them at 24 degrees from edgewise, about the best it'll be for many years. Welcoming rings. Welcoming rings. Come see us. Then in the pre-dawn sky, if you're up before dawn, see Mars low in the southeast before dawn, looking kind of reddish. And if you have trouble finding it, look for it on April 3rd or 4th.

The moon will be nearby. But the big news coming up is a solar eclipse that occurs on April 8th. You've been teasing us with this solar eclipse for weeks now. I don't want anyone to miss it who has a chance to see it. So perhaps I've overcompensated, but it really is coming. I swear. And it's a funky solar eclipse. That's the technical term. Or was it hybrid? I guess it's hybrid, not funky. And so it's total in the center of the path. And it's a funky solar eclipse. That's the technical term. Or was it hybrid? I guess it's hybrid, not funky. And so it's total in the center of the path and annular out towards the side, meaning that you still see the annulus, the ring of the sun, around the moon off on the ends.

But this is visible, which is what people really want to know. If you're hanging out in the South Pacific, that's where you want to be to see the total eclipse. If you're in South America, Central America, and even up into Southern and Eastern North America, including the Eastern part of the United States and Southern part of the United States, but not here, you can see a partial eclipse from those areas. So I wonder if some of our many listeners in New Zealand and Australia are going to be in totality. Yeah, well, I think they're going to have to road trip to do it. I honestly don't remember the details. Check the graphs on the web.

We'll give you a link to a place to find information about the eclipse. But I believe it starts just east of them. But if we've got people hanging out on Easter Island or Tahiti, or better yet, on a cruise ship, then they'll do pretty well. All stuff we should do. We should be there, don't you think, to report back to people? Speaking of on location, road trip! All right, on to this week in this history, in space history. This week in space history, on March 29, 1974,

Mariner 10 became the first spacecraft to fly past Mercury, giving us our first view of that inner planet. On to Random space fact! The highlands of the moon are mostly anorthosite. This is stuff that floated up when there was a giant magma ocean covering the entire moon, and the light stuff floated to the top and crystallized, and that is stuff called anorthosite, which you do find on Earth, but not nearly as prevalent as the highlands. Those are the bright areas if you look up at the moon.

Ah, never heard that term before. Well, that's what I'm here for, Matt. Trivia. On to, well, I didn't think it was that trivial. Oh, the trivia contest, I'm sorry. Yes, we asked you in the last time around, we asked you, I'm sorry. Yes, we asked you in the last time around, we asked you what human or humans have traveled the farthest from the surface of the Earth?

Who reached the highest altitude? How did we do, Matt? We did great. The listeners did great. Lots of answers. Only a couple that were wrong. We had one person pick out the right Apollo mission but said he didn't know who was sitting in the right hand seat, because I guess the assumption was that might have been the person farthest from Earth as it swung around. But we did have a winner. Ryan Caron of Amherst, New Hampshire, a longtime

listener, who said that it was none other than Jim Lovell, Fred Hayes, and Jack Swigert of Apollo 13. Well, congratulations. Yes, Apollo 13. And apparently I read that Jim Lovell actually was asked who was in the farthest seat. And he has refused to say. So we don't know. But at least we give it to the three-level Swigert and Hayes setting the altitude record. We give it to the three-level Swigert and Hayes, setting the altitude record. Turns out, primarily because more than the emergency trajectory they were taking,

it was actually tied to the fact that the moon was near apogee. The moon's orbit is somewhat elliptical, and it was the closest to apogee of any of the Apollo launches. Apogee being that point in the orbit when it is furthest away. Exactly. Out there at the ends of the ellipse. Farthest from the Earth. Okay, on to the next question for next time around. I'm going to stick with the Apollo theme for a change and ask you, what was the name of the Apollo 10 lunar module?

All of these spacecraft had at least nicknames. What was the name of the Apollo 10 lunar module? To enter, go to planetary.org slash radio. Find out how to email us your answer and take a chance at winning a fabulous Planetary Radio t-shirt. And get those entries into us by Monday, April 4 at noon Pacific time. Monday, April 4, noon Pacific time to make sure that you are eligible in this newest space trivia contest from What's Up and the mind of Dr. Bruce Betts.

I think we're done. A scary place indeed. Everyone go out there, look up at the night sky, and think about what Matt would look like without headphones. Thank you, and good night. No one will ever know. That's Dr. Bruce Betts. He's the director of projects for the Planetary Society,

and he does join us every week here for What's Up. That's it for Planetary Radio this week. Whether you're new to the show or one of our veterans, we'd love to hear from you. Write to planetaryradio at planetary.org. And tell us what you think of our little way station among the stars and planets. See you next time.