Planetary Radio: Space Exploration, Astronomy and Science - Peering Down at Huygens: Cassini Revisits Mysterious Titan

Episode Date: November 7, 2005

Steve Wall, deputy leader of the Cassini RADAR team, on new images of Huygens' landing site and a shoreline. Asteroids on Q&A, new What's Up Contest.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Cassini peers down at Titan and the Huygens landing site 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. The Saturn orbiter flew right over the spot where the European Space Agency's Huygens probe settled down on Titan last January. I'm Matt Kaplan. Postline that got imaged a few weeks ago? We'll hear the beginnings of answers to these questions from Steve Wall, deputy leader of the Cassini radar team at the Jet Propulsion Laboratory. Later today, Bruce Betts explains how one of our listeners will get to join us for a What's Up segment. First, though, just time enough for these space headlines. Two more moons at Pluto?

That's the tentative conclusion reached by a team relying on the Hubble Space Telescope. The details are at planetary.org, and we'll try to get lead researcher Alan Stern back on the show to talk about these discoveries. Hayabusa hiccups. Mission directors aborted release of the little Japanese probe's lander. It was to make a trial run at asteroid Itokawa in preparation for the first of two sample collecting visits. Again, you'll find the complete story at planetary.org. And NASA has just announced that Jeffrey Hanley will manage Project Constellation. That's the agency's new name for the program

that will develop the crew exploration vehicle and all other components that will make the vision for space exploration a reality. Hanley has been with NASA for more than 16 years. Emily's up next. She's organizing her rock collection this week. I'll be right back with Cassini's Steve Wall. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, what are the different families of asteroids? There are many different ways to classify asteroids,

but the first classification that's applied to any asteroid is a name based upon where it's found in the solar system and what kind of orbit it has. Most asteroids are found within a region of the solar system called, appropriately enough, the main asteroid belt. The main belt occupies space between the orbits of Mars and Jupiter, or from about twice to about four times Earth's distance from the sun. There are many thousands of main belt asteroids, and they are all under the gravitational sway of Jupiter. Even more dependent on Jupiter is a small group of asteroids known as Trojans. thousands of main belt asteroids, and they are all under the gravitational sway of Jupiter. Even more dependent on Jupiter is a small group of asteroids known as Trojans. There are two points on Jupiter's orbit, 60 degrees ahead and 60 degrees behind the planet, where the gravitational effects of the Sun and Jupiter balance. A few hundred Trojan asteroids sit in these points on Jupiter's

orbit. A small group of objects called centaurs wanders around the outer solar system among the orbits of Jupiter, Saturn, Uranus, and Neptune. Their orbital paths are unstable because of the influence of the giant planets. What about asteroids in the inner solar system? Stay tuned to Planetary Radio to find out more. Steve Wall, thanks very much for being only the latest member of the Cassini-Huygens family to join us here on Planetary Radio. You're very welcome. Glad to be here. Now, we brought you in in particular because there has been a heck of a lot happening with

your instrument, the radar instrument, on the Cassini spacecraft. And I guess what's most recently in the news, just in the past few days, is that you guys have now made a flyby over exactly the area where that little European probe set down on that strange moon. Right, and this actually has been a big event now for several of our planetary missions. For example, way back in the 70s when we landed on Mars with the Viking lander for the first time, Viking landers,

one of the big things was to try to find out where in the pictures we were taking from orbit this little thing actually descended. And that, believe it or not, is a huge task because you take the Huygens probe or the Viking lander, they're both things that are maybe the size of a kitchen table, or in the Viking lander case, about the size of a small car. But this is such vastly different scale

from the kind of thing when you're taking pictures of part of a planet. You make the connection between this big globe that you think of as a planet and really things that are more familiar to you in day-to-day, like where something small like a car or a table-sized thing would land. It's a big moment and has been now for several of our planetary missions. And I know the same things happen on Mars with Spirit and Opportunity and even the heat shield and so on, the aeroshell. It would help, of course, if you knew exactly where to look.

Sure. And we had one advantage this time, and that was that we had fairly accurate tracking of the probe as it went down. Now, that's on the scale of miles or kilometers. scale of miles or kilometers. But once it got down to the very few last seconds, even the Huygens probe got blown around a lot by the wind. And it's not clear at all exactly what happened between the way that it spun and the way that it rocked at the end of its parachute and the way that it got blown around by the winds. We don't know exactly how it landed. And so therefore, we have some doubts as to exactly where it landed. There's radio tracking and other things that we're still trying to piece this puzzle together.

But the big thing, and maybe the most visually exciting thing, is to try to find out if there's something you can see from that landed standpoint that you can also see from the orbital perspective. And how close are we getting to that? Because the images that have been published so far, both on the Cassini website from JPL, but also in a nice article by my colleague, Emily Lakdawalla, that's now at planetary.org, it's not real clear yet, but I guess there's some indication that things may be getting better, clearer. That's true. Over at JPL, when we first got the synthetic aperture radar data, the highest resolution data the radar can take,

and the highest resolution data really that we can get of Titan with any instruments, we got the picture first, started looking for anything that you could tie together, and we had the Huygens descent mosaic, the pictures that it took as it landed, and we spent a long time puzzling over, well, does it belong here? Does it belong over here? Does it belong over there? We brought in the data from the camera and from the infrared camera that we call them ISS and VIMS and tried to piece it together there. And for a while, it looked pretty grim. I mean, it was looking like it was hard to find things. In the past few days after we went home and got all asleep, we have made it a little bit clearer story.

But you're talking about a lander that we are a probe. We knew where it landed within maybe 20 kilometers. We have pictures now that have resolution that's like half a kilometer. So you're trying to locate now something to a factor of like 30 or 40 within the scale that you knew where it was. Yeah. Well, we're getting better. We found, you know, a mountain over there on the horizon that maybe matches. We found a sort of a V-shaped feature, don't know what it is, in the infrared data that looks like it might correspond with something that we saw in the descent data. And now the SAR images and these things that we've been calling cat scratches, it looks

like we might, and we don't know yet, but we might be able to see something like that over in the horizon. So we're slowly narrowing it down. We're going to come back to those cat scratches. But to be really clear, with a half-mile resolution, obviously you're not going to pick out this little probe sitting on the surface of the moon. First of all, yes, it's absolutely right. You're not going to see something

that's the size of that probe from an orbital camera. The best that you can do is to sort of look around from the perspective of the probe and see what you can match that might be of greater scale. It's something like being out in the desert, trying to look around for things that you can match that might be of greater scale. It's something like being out in the desert,

trying to look around for things that you can recognize on a topo map. We'll be back with more from Steve Wall of the Cassini radar team right after this message. 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. We didn't just build it. We attempted to put that first solar sail in orbit, and we're going to try again. You can read about all our exciting projects and get the latest space exploration news in depth

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We're talking Titan with Steve Wall, deputy leader of the Cassini radar team that has been snapping spectacular yet puzzling pictures of the big moon's surface. It's not really very much like using a regular camera. This is radar. You're not doing this in the light that's available, the dim light that's available from the sun. You're bouncing this stuff off of the moon, comes back up, and turning it into an image with lots of processing. Right.

And so one of the biggest problems that you have is that the pictures that we took from the probe were taken, like you said, in basically visible light. Not a whole lot of light, sort of orange filtered by the atmosphere. We took some pictures there. Now, radar cameras are sort of an odd beast. A radar camera is sort of a combination between the radar, like you think of as used by the military or by a jet that lands at an airport and a flash camera. Because you're looking, number one, at a picture that is in a completely different realm of the electromagnetic spectrum from what your eyes are used to.

So it doesn't make bright things bright. Radar has a tendency to make things that are rough bright. So the difference between looking, let's say, at a parking lot and looking on a gravel road are the kind of differences that would make a bright thing in a radar picture or a dark thing in a radar picture. So you have to use your mind's eye to see how would a radar camera see what I'm seeing in these pictures from the probe. The very, very challenging thing to do unless you spend a lot of time. That's why some of us spend a whole lot of time looking at pictures of the Earth that were taken with normal cameras and pictures of the Earth that were taken with radar cameras

to try to get that sense of what looks alike, what looks different. Really retraining your senses. It is. It is. It is. Mike Kobrick, who's a colleague of mine at JPL, wrote an article one time called Alien Eyes. And I think it's a great way of saying in a very few words the way that you have to look when you look at a picture that was taken with a radar camera. That just strikes me as extremely cool, actually. Yeah.

What we're doing is by a series of e-mails and meetings and telephone conversations, we're saying, should we move it a little bit to the left? Should we move it a little bit to the right? Should we move it a little bit north, a little bit south? Still a lot of conversation going on. I think by this time, let's say closer to Thanksgiving, maybe in a couple of weeks, we'll probably have it to the point where we're ready to say, we know right where that thing is.

And eventually you're going to get some help from another pass, right? Because then, and I think this is so cool, it's sort of Cassini's version of the Heisenberg uncertainty principle. You can't look at something and see how high it is. Use your altimeter at the same time. That's right. The way that this radar works, it uses one antenna, and that antenna both acts as the flash of the flash camera

and the lens of the camera for the radar. It also acts as our altimeter. In other words, the thing that we use to measure how far away Titan is. It acts as our radiometer, a whole different type now, where we essentially look at how away Titan is. It acts as our radiometer, a whole different type now where we essentially look at how warm Titan is, but it can only do one thing at a time. So when we pass Titan, we will, from a long way away, we'll start measuring temperatures. We'll measure temperatures along large portions of the disk of Titan that we can see. Then we switch to another mode called scatterometry, where we scatter signals off and just tell something general about the

surface. Then we switch to altimetry, and we take a track that shows us what the bumps are, if you want, on the surface. Then we do the synthetic aperture radar, where we take the high-resolution pictures, and then we do the whole thing over again backwards as we leave. So there's a whole bunch of different modes. Then, just to give you an idea of how bizarrely complicated this gets, we combine that with what the camera, the infrared spectrometer, our ultraviolet imaging spectrometer, our magnetometers, our fields and particles instruments. A total of 12 instruments. Each of them has probably as many modes as the radar does.

I don't know. But there are literally dozens, many dozens, of different things the spacecraft can do. There are a whole lot of very dedicated people over at JPL that spend a whole lot of time trying to figure out exactly what the right sequence is. It's like taking a car through a city you've never been in before, wanting to look out all of the windows with all of the different pairs of eyes in the car, all at the same time. This is so fascinating, but I want to make sure we talk some more about Titan and what you have learned. Why does this moon have cat scratch fever? Good question. Cat scratches are one of the more unique things we've seen on the surface,

among a whole lot of unique things. We took our first data just about a year ago, in October of 2004, saw some interesting things, but we thought we sort of had a handle on what they were all like. Then in February, we took another stripe across the surface of Titan, and we saw these first little patches that we called cat scratches. And they're patches maybe 50 to maybe 100 kilometers across, parallel lines. They look for all the world like a cat just went down the side of the planet. Each one of the little lines about a kilometer or two apart. Sometimes these lines

merge and sometimes they separate, so they're not completely just parallel lines. But it's unlike anything that we've seen before. It resembles most closely a set of sand dunes on the Earth, seen from an orbital perspective. Now we're getting out all of our pictures of all the sand dunes that we know of on the Earth and trying to compare those to these cat scratches because the most obvious thing is that they're formed by wind. Now there are other possibilities, but that's the one we're sort of focusing in on. Now we know that the winds on Titan are not very strong, and it does take a certain kind of wind to form a sand dune on Earth.

So that has us a little bit puzzled. of wind to form a sand dune on Earth. So that has us a little bit puzzled. But it's most likely that there is something that gets ground up into dust or dirt-sized particles that forms dunes on Titan. But parallel lines hundreds of kilometers

long? Well, in the latest data that we got last Saturday, we do find these things that go on for many, many, many, many, many tens of kilometers, probably overall hundreds of kilometers, that we think follow the zonal winds on Titan. We don't know that much about how winds go on Titan, but it looks like they actually separate around hills, so like the wind would.

They don't bounce off of hills, so they're probably not waves. That's another possibility. But they're most likely to be entrained by the wind. Now, where do you find a place where wind is constant for long enough periods of time to form dunes over that distance? That's the puzzle. We're almost out of time. Oh, my goodness.

I know, and this is so much fun. We've got to talk at least about some results that came back a few weeks ago. Okay. And these were the indications that maybe you found the place where surf stopped on Titan. Well, it's possible. You're talking about some data that we took in September. But, yes, we found a very dark-looking area, unfortunately right at the end of our observation, so all we saw was a piece of it.

But the margin between this very dark-looking area and the more typical terrain that we've seen so far looks for all the world like a coastline. It has bays. It has perhaps little off-lying islands. There are some intriguing places that look like perhaps the liquid, whatever it was, if it was a liquid, flooded into like a wetland. It might be a wetland on Earth. Now, remember, we're talking about a place that is 150 degrees below zero. Right.

So the first thing we have to ask is what kind of liquids are there? Well, methane is a liquid at that temperature sometimes, so that's a possibility. If you put ammonia into water, it's a lot like putting antifreeze into water in your radiator, and it can stay liquid that cold. There are some organics that we think may be typical on Titan that may be liquid, but we didn't think they were quite that free-flowing a liquid, but we didn't think they were quite that free-flowing a liquid. So we're confused. Do you ever get together at your favorite bar with the rest of the radar team and think, or anybody else on the Cassini team, and speculate on what that ocean would look like? I mean, would it behave like an ocean on Earth if it's there or if it was there in even ancient times of Titan?

I mean, would the waves look like they do here on Earth? I should have worn my surf Titan T-shirt today, but I didn't. Well, I mean, the answer is yes, of course. I mean, we love to speculate. Try not to do it in print, but try to be more considered when we do that. But, yeah, we always wonder, once you've given the possibility of liquids, are there waves? Well, you can do that calculation, and you can tell that the waves are not going to be real high. But, yeah, there would be waves on liquids.

We tend to ask, well, would there be things floating in there? Well, the answer is there aren't very many things that float in liquid methane. We're putting together the picture. You know, whether there are areas to surf in or not, that's something for another time. Well, maybe we'll paddle around a little bit. We are out of time. This is fascinating. Obviously, we have to tune in again as you learn more about all of Titan, but in particular that one site where the Huygens probe set down.

Hopefully you'll have that altimetry. When does that take place, when you get the altimetry data? We have a little altimetry at the end of every pass. We have some from our first four encounters that we've looked at a little. It's a pretty flat place from what we've seen so far. We'll know more as we take more data and as we process more of the data that we've got. Just one last question. Is there a Cassini radar team bar that you guys hang out at and speculate? Well, we have a restaurant that also contains a bar that we tend to go to down in Pasadena,

and it's a place that we get together and think about those things that, as you say, are more speculation. Think about what it might be like if you were actually on the surface of Titan. It's a pretty congenial team. We have a good time. Well, raise a toast to us sometime, and we'll do the same for you. Thanks so much, Steve Wall, for joining us today on Planetary Radio. You're very welcome. Steve Wall is the deputy leader of the radar team for the Cassini spacecraft,

continuing to circle that great ring planet of Saturn and, whenever it can, pay special attention to one of the most mysterious bodies in the solar system, Titan. And we'll be back with Bruce Betts, who's generally not much of a mystery, but it'll be this week's edition of What's Up right after this return visit from Emily. I'm Emily Lakdawalla back with Q&A. What families of asteroids lie in the inner solar system? Within the main belt, there are asteroids that travel among the orbits

of Mercury, Venus, Earth, and Mars. Of particular interest to earthlings are near-Earth asteroids, which are defined as asteroids having orbits that bring them within 1.3 times Earth's distance from the Sun. Near-earth asteroids are further split into three groups Amors, Apollos and Ottens. Amors cross Mars's orbit but don't quite cross Earth's. Apollos have orbits that cross Earth's and take more than one year to orbit the Sun. Ottens cross Earth's orbit and take less than one year to orbit the Sun. Ottens cross Earth's orbit and take less than one year to orbit the Sun. These Earth-crossing asteroids present possible future Earth impact risks, though no near-Earth asteroid is now predicted ever to hit Earth.

Finally, there are the elusive vulcanoids. These are asteroids that are theorized to orbit the Sun inside the orbit of Mercury. There should be some of them out there, but no vulcanoid has yet been discovered. 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 with Dr. Bruce Betts, the Director of Projects for the Planetary Society.

He's here to tell us about the night sky and more. Oh, so much more. We're going to do a tease. We're going to do a tease because if people stick around to the end, they're going to find out how they might be able to join us. Join us for What's Up. Join us on Planetary Radio. Stay tuned. First, let's talk about what's in the us on Planetary Radio stay tuned

first let's talk about what's in the night sky Mars still glorious beautiful starting to fade a little bit still brighter than any star at the time we're recording this and it will fade over the next few weeks so if you haven't gone out or even if you have go see Mars it's rising about sunset

in the east and we'll be setting around dawn in the west, very high overhead during the middle of the night, orangish-looking bright thing. In the evening sky, you can also see Venus, of course, very, very bright, low on the other side of the sky in the west. And you can see Saturn in the middle of the night, rising around 10 or 11 p.m. roughly, and very high in the south around dawn. around 10 or 11 p.m. roughly, and very high in the south around dawn.

And Jupiter is a tough call, but just starting to come into view very low in the east-southeast before dawn. Bad meteor showers happening right now, which normally I wouldn't mention and would not make you suffer through it. But the torrids, named after Taurus, are actually seeming to produce some fireballs. So there still aren't very many meteors per hour. Taurids are usually so low down the chain that you never mention them. Yeah, I want to point out that when you say a bad meteor shower, that's not that the Earth is in danger. It's that they're boring.

Bad meteor shower, bad meteor shower. You're right. Exactly right. Good call. And even a fireball, as scary as it sounds, is like something the size of a piece of gravel that's burning up in the atmosphere, even sand. I've only seen a couple. They're great, though. They are good stuff.

So the torrids have a bit of a peak, which was actually predicted many years ago because we're going through the dirt stream of Comet Enki, and that's what causes the torrids, and we happen to be going through a richer part of that this time around. So still not very many. The torrids typically have like five per hour in terms of at its peak. They peak between the 7th and the 12th of November. I mention it because of a little fireball attention, so go out there, have fun with them. But we'll keep you posted for the better meteor showers coming.

This week in space history, nine years ago, Mars Global Surveyor was launched, still working fabulously at Mars. On to Random Space Fact! In honor of Pluto apparently having two newly discovered moons. Oh, yay. to you that Charon, or Karen, or Sharon, or however you pronounce Pluto's big moon, is a whopping half the size of Pluto in terms of its diameter. This is a much bigger ratio than any other planet-moon system that we have in our solar system. The next largest duo is, of course, the Earth-Moon pairing, but the Earth is only a quarter

of the size. That's diameter of volume. They're much, much tinier. But let's go on to the trivia contest. We asked you, what planets in our solar system share parts of their names with elements in the periodic table? How did we do, Matt? Wow, lots of great answers, much more than we were expecting from people. And one we've got to give special attention to, recent winner Carlos Castañon Jimenez,

who writes to us just about every week, I think. He came up with one that we did not have in mind. Tellurium, which is based on the Latin word telus, meaning earth. And so, Carlos, special mention. But our winner this week is Amanda Altobelli, who hails from Yorktown Heights, New York. She came up with the ones that Bruce and I knew about. Neptune, Neptunium, Uranus, Uranium, Pluto,

Plutonium, and Mercury. Mercurium. Wait, no, no. Mercury. Darn! Ah, you're so mercurial. Well, that is very interesting. You know, of course, the question we meant to ask, was based on the modern English versions of the names. We should have been clearer.

But still, we threw them into the random mix, but we got our winner. Good on us, Carlos. And Amanda, you're going to get that Planetary Radio t-shirt. Wear it in good health. We learned so much on this show. I love it. All right. If you'd like to win a Planetary Radio t-shirt, answer the following question.

How many parsecs in a light year? That's both units of distance measurement. I should know this because I knew this once upon a time. Yes, but you're not allowed to enter. Yeah, I know. But all I can remember is that Han Solo said the Millennium Falcon can make two-point-something parsecs past light speed. Would I win if I could enter on that? No, actually, you wouldn't.

It's a cool reference and all, but since parsec is a unit of distance rather than speed, oddly enough, it didn't make that much sense. Lucas was playing with us. He knew what he was doing. He had a good laugh. Let's tell people how they can be on WhatsApp and join this festival as frenzy. Just before we do that, I do want people to know that they have to get that entry to us by the

14th. That's Monday, November 14th at 2 p.m. Pacific time. Tell us about them, their Parsec things. Oh yeah, and enter at our website planetary.org slash radio and you will see the gloriously redesigned Planetary Society website. And that's where people would find the auction.

Part of our 25th anniversary and tied to our 25th anniversary dinner, we have an auction with lots of nifty things that you can bid on. Now, you have to get your bids in by November 12th at 8 p.m. This is being done in an eBay-like auction. You can find links to it on our website. One of the things you can bid on is the ability to party with Matt and I. Well, okay, but you can help us record What's Up and help him improve the quality of our show. Maybe do a random space fact.

Doubtless they will improve the quality of the show by their mere presence. So bid. We'd love to have you join us for What's Up. In the meantime, everyone go out there, look up at the night sky, and think about why slippery when wet. Why is slippery when wet? What is slippery when wet? Why? Why? Why? Well, he's Bruce

Betts. He's going to slide on out of here because we're done with this edition of What's Up. Something special next week will bring you highlights from the celebration of the Planetary Society's 25th anniversary, featuring Ray Bradbury, Bill Nye, Director James Cameron, and much more. I hope you'll join us.

Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week, everyone. Thank you.