Planetary Radio: Space Exploration, Astronomy and Science - Cassini Visits Phoebe at Saturn!

Episode Date: June 21, 2004

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Cassini meets Phoebe on Planetary Radio. Hello everyone, I'm Matt Kaplan. The Cassini-Huygens spacecraft has had its first close encounter with Saturn, or rather with one of Saturn's moons. The images and data collected from tiny Phoebe are spectacular. We'll talk about Phoebe and its much bigger neighbor, Titan, with planetary scientist Elizabeth Turtle. Later, you can join Bruce Betts and me at Legoland in Southern California as we give away some T-shirts. First, though, we'll hear what Emily has to say

about the possibility of life on Mysterious Titan. I'll be right back. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, how likely is it that there is life on Titan? On the face of it, Titan, Saturn's largest moon, doesn't seem to be a promising spot for life. Its surface temperature is minus 180 Celsius, minus 290 Fahrenheit, far below the freezing point of water. Celsius, minus 290 Fahrenheit, far below the freezing point of water. But Titan's cold atmosphere is rich with organic molecules, the carbon-based molecules out of which all Earth life is composed. Titan's atmosphere is made mostly of nitrogen and methane. In

the upper atmosphere, these molecules are broken up by bombarding electrons from Saturn's energetic magnetosphere. The broken-up molecules recombine into more complex, heavier molecules, which settle down onto Titan's surface. Laboratory simulations suggest that, over geologic time, at least 100 meters of organic muck should have fallen onto the surface. Could this stuff have made life on Titan? Stay tuned to Planetary Radio to find out. I knew we had to have Elizabeth Zibby Turtle back on the show as soon as I heard how thrilled she was by the new super-sharp images of Saturn's moon Phoebe,

taken by the Cassini-Huygens spacecraft. Zibi is now an assistant research scientist at the University of Arizona's Lunar and Planetary Lab. That's where she watched the pictures of Phoebe arrive. And it's also where she took a few minutes to chat with us. Elizabeth, or should I say Zibi, welcome back to Planetary Radio. Thank you. You were pretty excited as you saw those images of Phoebe coming in a few days ago. Oh, yeah, yeah. It was a spectacular weekend.

So you were, what, sitting at your desk waiting as each one of these rolled up on your computer? Yep, yep. I was sitting in the office refreshing the image database that we have as the images got played back. Now, we've mentioned that what you're really looking forward to, because you're much more involved with it, are the upcoming observations of Titan. And we're going to talk about Titan, hopefully at some length. But let's start with Phoebe. Even though you've said that this is not your main field of study, I mean, clearly you were fascinated by these great images, but were they telling us anything interesting? I know there was some talk that there might be some layering

revealed by some of these meteor hits. There are hints of that in one of the crater walls, an image that came back, and that actually was one of my favorite images. I haven't studied Phoebe or small bodies in the solar system, but I have studied impact cratering. And so I was kind of focusing on the impact craters because of my background with them. And one of the craters just jumps out as having this very fresh, sharp rim

that actually has dark material right around the edge, and then there's brighter material that's been moving down the slope into the crater. And there are hints of layering. We can't say conclusively, given the resolution limits of the images, which are quite high resolution, but we can't say conclusively that they're layers. There are certainly hints of layers, and that's very interesting. It looked like the best resolution I could find on the Cyclops site,

which is the place to go if you want to see Cassini images. Easiest way to get there, folks, by the way, go to our site, planetary.org slash Saturn, the special site set up by the Planetary Society to follow Cassini-Huygens mission. And there is a link there to Cyclops and also to the main Cassini site. But the best of those images, as Cassini made this close pass, I guess closer than about 1,500 miles or so, was about 45 feet per pixel, which is pretty good, I guess, but you wish it had been even sharper?

Well, it's spectacular resolution. It's the best view we've ever had of Phoebe, the best view we will have. Cassini won't get this close to Phoebe again. This is the only flyby as it approaches Saturn. So I'm not complaining about the resolution, but as with any imaging experiment, there's only so much you can do from 2,000 kilometers above the surface of a planet. You had some question in your mind, and I think I heard a bit of that, as to whether this layering is even really there on this fresh crater

that's seen in this maybe the most famous image from the flyby. Possible it was a trick of the light? I mean, has that been resolved a little bit? No. The uncertainty I have is that if you look at the images and you zoom right in, you can actually see dark material and then bright material and dark material. What you can't tell is whether that bright material in between the two apparent dark layers is actually a layer or whether it's actually just material sitting on top of the surface.

And that's an ambiguity that you can't really resolve without going there and exploring the surface. And that's an ambiguity that you can't really resolve without going there and exploring the surface. And that clearly is something that's a ways off. Well, we'll put that on the things to do list. Right. I wonder if you've had any more thoughts about Phoebe's origin. I mean, there was a quote from you in a great article by my colleague, Emily Laktawalla, questioning whether Phoebe might have been an asteroid and concluding that, no, it doesn't look like an asteroid anymore. The observations that we have, and I should say that I've been working with the imaging team,

but there are many other instruments on board the Cassini spacecraft that took data during the flyby, the visible and near-infrared mapping spectrometer, SEERS, as well as the radar. I apologize for the instruments that I haven't named. There have been quite a lot of observations made. But the observations that we see, the images that we see, are consistent with an origin in the outer solar system, an ice-rich body.

What we see is a fairly dark surface, but there are areas where there's very bright material exposed, either by cratering or by small landslides that have occurred. And so that suggests that it's ice-rich, and that's information that we're expecting to be confirmed by, as I mentioned, the VIMS instrument, the Visible and Near-Infrared Mapping Spectrometer. And that is this interesting instrument, a spectrometer, but one that actually delivers an image as it gives you clues to the composition of what it's looking at? Yes, yes.

Their imaging as well, although they have a lower spatial resolution, as well, although they have a lower spatial resolution, they have a much higher spectral resolution starting in the near-infrared and going out into the mid-infrared, I believe. And so they can actually, with that high spectral resolution, look for features due to water ice and other surface materials. So they'll be able to really help understand the composition of Phoebe's surface. Well, I know there has been speculation that Phoebe might have been a captured object, perhaps similar to one of those out in that distant place called the Kuiper Belt. Is that what you're thinking when you're saying from the outer reaches of the solar system?

Yes. Yeah, it's thought that Phoebe is a captured object because of its orbit. It has an unusual orbit. It orbits in the opposite direction. It's retrograde from the other orbits of the other satellites and the spin of Saturn itself, and it's highly inclined. And so it's thought that it's a captured object. It may be an object left over from the very formation of the solar system.

It's billions of years old. We're going to take a break in a moment and move on to Titan, which everybody, of course, is looking forward to. One of the major objectives of this mission is to explore that mysterious moon, and one of your major objectives. But just one more comment about the first, these incredible images of this pockmarked little satellite that has weathered so much. I guess that's what generated such strong feeling, not only on your part, but a lot of scientists?

Yeah, the images really are spectacular. And I think one of the other things that's been so exciting is how different they are from other small bodies we've seen in the solar system, from the surfaces of asteroids. Just the range of surfaces we see in the solar system is continually surprising us. Well, we'll go ahead and take that break, and when we come back, we'll continue this conversation with Elizabeth Turtle Zibby about Titan, something that she and the rest of us are looking forward to very much. We'll be right back with Planetary Radio. This is Buzz Aldrin.

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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. Zibi is our guest on Planetary Radio this week. More formally, Elizabeth Turtle. She is an assistant research scientist at the Lunar and Planetary Lab, University of Arizona. Zibi, let's move out to, or move in, I should say, a moon that has been puzzling scientists

for a lot longer than Phoebe, and one that I guess you and a lot of other researchers are hoping to learn more about in, well, beginning in just a few days. Yes. Titan's been a mystery for quite a while. It has a thick atmosphere, which prevented Voyager from observing the surface in any detail. In fact, it was thought that Voyager hadn't seen the surface, although it's been recently demonstrated that Voyager did see down to the surface. It's possible to see the surface through spectral windows in the atmosphere, and the Hubble Space Telescope and some ground-based

observers as well have imaged the surface. But Voyager wasn't really designed to peek through that thick atmosphere, and Cassini is. Yes. Cassini carries filters that are expressly designed to look through, to take advantage of these windows that I mentioned in the atmosphere to see down to the surface. How good a view of Titan are we going to have? And we're going to have several, aren't we? We hope. Cassini will perform 76 orbits of Saturn in its nominal mission, and there will be 45 close flybys of Titan. Wow.

At this point, it's not actually known yet how well we'll be able to image the surface. And that's because the scattering properties, the way that the lower atmosphere of Titan scatters light, aren't known absolutely. There are plenty of models, and they suggest that we'll be able to image it at high resolution, but it's actually possible that we won't. And so we're waiting with bated breath not only to learn about Titan, but to learn about how much we'll be able to do with the imaging system. Is this atmosphere of Titan just one of the things that makes this moon so interesting and unique?

It certainly makes it unique. It's the only satellite in the solar system with such a substantial atmosphere. It certainly makes it interesting because it can have weather processes that you don't have elsewhere in the solar system. And it's also just heightened the excitement because it's such a mystery. There has been endless speculation about the surface of Titan. Can you talk a little bit about what we might find there and even maybe some of the wilder speculation? Well, we certainly expect to find impact craters as we see throughout the solar system. But as I mentioned, there may be

weather. And in fact, there may be hydrocarbon lakes on the surface, or even rivers. There may be erosional processes due to precipitation from the atmosphere. And these, as I've said, are processes that we just don't see on other icy satellites. And not water erosion, but erosion caused by this flowing hydrocarbons. I mean, like what, gasoline? Essentially, yeah. And other, I mean, I know there are thousands of hydrocarbon compounds, but, I mean, this would be quite a landscape, I would think, if this turns out to be the case. It certainly could be.

And we're only starting to get glimpses of it. We've been taking images as we're approaching, as Cassini's approaching the Saturnian system and starting to see albedo markings on the surface that are consistent with observations that we've seen, as I mentioned, with the Hubble Space Telescope and ground-based observers have made maps of the surface, and we're getting slightly better resolution.

But the first real test will be right after Saturn orbit insertion when we have a distant flyby of Titan, but nonetheless the best view that we will have seen. If the camera and the atmosphere cooperate, then we'll hopefully be observing features as small as a few kilometers. And that'll be during the later flybys, or is that during this first one? That's during the flyby right after Saturn orbit insertion. On the 2nd of July, Saturn orbit insertion is the night of the 30th of June,

and on the 2nd of July, there's a 340,000-kilometer flyby of Titan. And that nominally gives us a pixel scale of two kilometers. Later on in the flybys that I mentioned, those are much closer. We get down to within a thousand kilometers of the surface of Titan. And were we able to image as we hope, the resolutions could be as low as several tens of meters per pixel. But as I say, that's still an outstanding question. So the 2nd of July will be the first big test of that. Clarify for us, before we run out of time, when we talk about X number of meters or feet per pixel,

if you can see some tens of meters per pixel, how small a feature on the surface of Titan would you actually be able to resolve and say, oh, look at that little crater? To really identify something, you need a few pixels. You can't identify something from a single pixel. So if the pixel scale is 50 meters, then you're really resolving features that are closer to 100 meters per pixel. We are just about out of time. Can we expect to see these images and other data coming back regarding Titan as promptly as we have from Phoebe?

I certainly hope so. I believe that's the plan, and I should state that there also are many other instruments designed to look at Titan. Specifically, there's a radar that will be sending back, an imaging radar that will be sending back images of the surface, and that, too, there is less question about the atmosphere for those data. So there's a lot to learn. And then, of course, much later in the year, the Huygens probe that we've talked about on this show, and if we had time, we could address, but it certainly is a topic that will be coming up repeatedly over the

next few weeks here on Planetary Radio. Zibi, we're going to put your website, your own homepage, and some of these other links where we normally do on the page where people can hear our show, but I want to mention again that if you want more news of the Cassini mission, go to planetary.org slash Saturn, and you'll have links there to these other sites that we've talked about. Zibi, thanks very much for joining us once again on Planetary Radio. Thank you. My pleasure. Elizabeth Turtle has been our guest.

That is her nickname, Zibi, that most people seem to know her by. She is an assistant research scientist at the Lunar and Planetary Lab, University of Arizona. I'll be back with Bruce Betts and What's Up from a special location, Legoland, right after this return visit from Emily. I'm Emily Lakdawalla, back with Q&A. Could a rich environment of organic materials have produced life on Titan? Most scientists, being scientists, are skeptical. But scientists hope that Titan is a fabulously interesting laboratory for our understanding of what conditions on a primitive Earth might have been like before life originated here.

In order to evolve, life on Earth would have required a supply of organic materials readily available in the environment. Therefore, to understand the origins of life, we need to know what kind of non-biological organic chemistry preceded it. Understanding Titan's chemistry is one of the motives behind the Cassini-Huygens mission to Saturn and Titan. The Cassini spacecraft goes into Saturn orbit on July 1st, just after midnight Universal Time.

Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. It's that regular segment in the Planetary Society's radio show, Planetary Radio, where we are joined by the Society's Director of Projects, Bruce Betts. And it's time for What's Up? Yeah! Okay, all right, all right, that's enough. You're not all getting shirts.

That was impressive. That made them sound like a real crowd. They are a real crowd, Matt. Stop talking like they're imaginary. Here we are at Legoland, California, live. Well, okay, not really. Close enough. But we're alive, and we're coming to you with What's Up.

You've got to explain why we're at Legoland. And we're coming to you with What's Up. You've got to explain why we're at Legoland. We are at Legoland this weekend because it is their debut of Florida Miniland. And it includes Cape Canaveral and parts of the Kennedy Space Center. It's very impressive. Have you had a chance to go up there yet, Matt? I have not been here since the opening of that section of Miniland, so I'm going to go over after the show.

It is fabulous. Yeah, I bet it is. And so they've got a whole space operation weekend going on here with lots of astronauts and then, you know, us. We had, well, he's gone now. We had an astronaut right next door. Yeah, he was here until you showed up. I have that affection.

Shall I tell people what's up in the night sky, man? Yeah, let's get started with that. Okay, well, still have one really good planet easy to see in the evening. Look off to the west, fairly high in the sky, and you'll see Jupiter looking like the brightest star-like object up there. Also, if you go out shortly after sunset, you can see Saturn and Mars low towards the horizon, still up, but getting harder and harder to see. If you're up before dawn, which I try not to be, you can see Venus looking extremely bright, brightest object before

dawn off there in the east. So good stuff to look at. You can still see comets neat and linear if you go out, and particularly with binoculars. They're tough to see without binoculars, but you can see them. You can go to our website, planetary.org slash radio, and we'll give you some links of how you can

figure out exactly where to look for those comets. Don't you want to mention the real names of those comets as named during our trivia contest? Well, of course, but I thought maybe people were getting tired of that. But yeah, we officially have renamed them Bucket Full of Marmots and Bob. Because that's so much more interesting than neat and linear and a whole bunch of numbers. So somebody won a shirt for that. Don't laugh. Look, I'm a night sky. linear and a whole bunch of numbers. Somebody won a shirt for that. Don't laugh. Look, I'm a nice guy.

It's a bucket full of marmots. You see, therein lies the humor. What else have you got? We've got random space fact. I'm going to steal one from the speaker that we had earlier here today. By the way, don't mention who he was. Yeah, an astronaut. And he reminded me that seconds

before the shuttle lifts off, they fill the area under the shuttle with millions of gallons of water. The primary reason, not actually being for heat control, although that's a lot of it, it's because of these sound waves to keep the sound waves from reverberating back up, reflecting directly back up off the concrete and damaging the shuttle. Very impressive. You can always see it in the launch footage of the shuttle. That's why they dumped millions of gallons of water out there. I like the launch where they added the Jell-O.

That really made it interesting. Yes, but the smell was odd. So anyway, this probably takes us along to our trivia contest. And shall we do the let's do last week's, this week's, and then some local trivia for the people who are here. How do we do? We once again had a record number of respondents. I don't know.

Something's happening with this show, or they just really want a shirt really bad. Well, look how cool this shirt is. Of course, not those of you on the radio, but those in person. Is this a cool shirt? Yeah! You're such shills. It is a nice shirt, and it's keeping me relatively warm on a cool day at Legoland. You missed the rain earlier, Matt. So I heard. Yeah, they had me speak earlier in the rain. Did you notice the tarp over us? Yeah. Yeah, there are holes in it.

It's not very waterproof, is it? We had a whole bunch of entries. Every one of them was correct. Everybody knew who discovered Phoebe. And it was William Henry Pickering. And he did it in 1898, right? 1898. Now, how did he do that? Over 100 years ago.

This is, Phoebe's a small rock. How did he find it? Very good eyes. Yeah, right. You know, he used a telescope. Yeah, but how big a telescope? I mean, I can't see. I've got a telescope. I wouldn't be able to see that little rock. Yeah, it was, you know, a pretty big one. All right, all right. I guess it was bigger then because it hadn't had so many things hit it. The telescope? No, Phoebe. It's all right. We're not talking about the last episode of Friends.

We're talking about the moon of Saturn that Cassini recently encountered, recording stunning images, which you can see on their website, or our brand-new Saturn section at planetary.org. Planetary.org slash Saturn. David Donald was the winner. David wrote in to us with the correct answer from Winnipeg in Canada, and he didn't have the date that we are got we did get that date of eighteen ninety eight from a lot of people uh... one of our

regular listeners dominic he wanted us to uh... not get confused with william hayward pickering former director of the jet propulsion laboratory so many people make that mistake yeah it's true i ran into three today okay new new New trivia contest. Okay, new trivia contest. What I would like to ask you this week, again inspired by the person who was here earlier today, so if you saw him, please don't shout out his name, because our trivia contest is, what astronaut commanded the first mission, the first shuttle mission, to include a Russian cosmonaut. What American astronaut commanded the first shuttle mission to include a Russian astronaut? How do they enter the contest?

And I had the happy circumstance to meet him earlier today here speaking at Legoland. They can enter the contest by going to planetary.org slash radio and following the instructions to enter the contest and win this glorious T-shirt. They're kind of losing interest there. We better hurry. All right. We better start giving them things. Get us your entries by Thursday, June 24, noontime.

Thursday, June 24, noontime, if you want your entry to be considered in this week's contest. That's for you guys who are listening on the radio. But how about the folks out here? We just have a couple of minutes left. All right. With a couple of minutes, we're going to ask some questions. We'll award you some prizes. You want to help me out here, Matt? Sure. We have three t-shirts, three different sizes. Not sure how to do this. Please answer the following question. What are the names of Mars's two moons? The names of Mars's two moons right here. Got to jump in. He was very enthusiastic, but now he's hiding. Anybody? Mars's two moons. The names of Mars' two moons right here. Got to tell me how he had it.

He was very enthusiastic, but now he's hiding. Anybody? Mars' two moons. The names? Here's somebody. Looking for the moons. The two moons of Mars. We might have to get to that in a moment.

Stay tuned. For those of you Latin fans, it's based on fear and panic. Oh, that helps. I've got fear and panic now. He's afraid we're not going to get off the stage. Oh, that helped. I've got fear and panic now. He's afraid we're not going to get off the stage. Oh, wait. There's someone in the back. They got it.

Okay, Phobos and Deimos. And there's an astrobot. All right, we're giving away Lego astrobots. We've got about a minute left. All right, what is the fourth planet from the sun? Fourth planet from the sun. Nice place to visit. Mars.

All right, we've got one right here. There you go. All right, now what's the name of the two rovers on Mars? Yes, indeed. Throw him a shirt. You got it. What are you looking away for? Here's your shirt.

All right. You're welcome. Okay, who. What are you looking away for? Here's your shirt. All right. You're welcome. Okay. Who discovered Saturn's moon, Phoebe? Turns out they were all sleeping during the broadcast. It was just a test. Yes. Yes.

Hickory. Very good. Here you go. Catch. All right. Good catch. Bruce, we are out of time. We're out of time.

All right. Well, maybe after this spiffy radio, we'll give out some wonderful prizes. That's too big? All right. You know what? Trade with him over there. He's got a small. You can trade with him.

He might want a bigger one. All right. Another problem solved. Bruce, say goodnight. Thank you, everyone. I want you all to go out, look up in the night sky, and think about Lego bricks. Thank you, and good night. Bruce Betts is the Director of Projects for the Planetary Society.

He joins us each week here on Planetary Radio, though not usually from Lego Lab. Just enough time left for a few program notes. Have you noticed that Planetary Radio is now available on the web as an MP3 file? We hope to soon have all of our past shows converted to this convenient format, along with the Windows Media files we've provided from the start. Check them out at planetary.org slash radio. And remember that we're almost ready to make the show available to public radio stations all over the United States. Let us know if there's a station near you that should be airing Planetary Radio. Thank you. They just put the first private civilian astronaut into space on Rutan's Spaceship One.

It could be the real start of spaceflight for the rest of us. Next week, we'll bring you highlights of the spectacular June 21st flight over California's Mojave Desert. Join us for a special Planetary Radio view of this history-making event. Have a great week.