Planetary Radio: Space Exploration, Astronomy and Science - Saturn Update From Cassini Deputy Project Scientist Linda Spilker

Episode Date: August 31, 2009

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Back to Saturn with Linda Spilker, 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 of the Planetary Society and do we ever have a packed show. Start it with Bill Nye's kudos to a team that has successfully tested a new kind of heat shield that could get us to the surface of Mars. Then it's time for one of our periodic updates from the Cassini mission's Linda Spilker. And boy has there been a lot happening a billion miles away at Saturn. Emily Lakdawalla will explain a bit more about the recent smackdown at Jupiter, and Bruce Betts will give us an up-close look at more than the night sky this time.

He's just a mile or so from the station fire, burning tens of thousands of acres in Southern California. Just barely enough time now to mention that Space Shuttle Discovery has reached the International Space Station, and to send our condolences to India's Chandrayaan-1 team, contact has been lost with that nation's first lunar orbiter. More details are in Emily's blog at planetary.org. Here's Bill. Hey, Bill Nye, the planetary guy here, vice president of the Planetary Society. Now, this week, the Augustine Commission's results are being debated. The former administrator of NASA, Michael Griffin, is complaining, saying that people must keep their focus on the moon.

We can't lose our—okay, and so on. But let me tell you what happened this week that was cool. NASA, with all the other stuff that's going on, all the other controversy, successfully launched and deployed the inflatable reentry vehicle experiment. This thing is an industrial fabric mushroom that inflated in space and came down through the Earth's atmosphere successfully. It had a little bit of spin to make it stable. And this is exactly the kind of thing that we need to do if we're going to go to Mars, whether it's with people or with robots. Because here's the thing. Mars has an atmosphere, but it's not much of an atmosphere. You enter the Martian atmosphere at any reasonable

speed, you're going about Mach 10. By the time you get down deep enough in the atmosphere where you could fly around with your airplane or something, you're going about Mach 0.6. That's a huge range. And things get torn apart and they get really hot under those kind of aerodynamic conditions. But the inflatable reentry vehicle experiment was a success. This is the future. This is the kind of cool thing that NASA's got to tell the world about. This is the future. This is the kind of cool thing that NASA's got to tell the world about.

Maybe it will now be a reasonable cost to go up into low Earth orbit, grab debris, bring it down safely, burn it up easily. Then maybe we can go to other worlds like Mars and walk around and look at rocks. This could be cool. All from the IRVI, the Inflatable Reentry Vehicle Experiment. Way to go, you guys. Good work. I've got to fly Bill Nye the Planetary God. We check in with Linda Spilker at least twice a year. The Cassini Deputy Project Scientist has been part of that magnificent mission since long before its launch nearly 12 years ago.

The bus-sized spacecraft has now been exploring Saturn, its moons, and its rings for more than five years and is in an extended phase called the Cassini Equinox mission. That's where our conversation started when I called her office at the Jet Propulsion Lab near Pasadena, California. Linda, welcome back and happy equinox. Oh, thank you very much. Yes, it's been a very exciting time here. The rings have been edge-on as seen from both the sun and the earth. And we have been talking about this off and on.

Bruce Betts brings it up regularly in our What's Up segment. I don't know that you're entirely ready to talk about everything that Cassini has learned during this special time at Saturn. No, we're still busy looking through the data, trying to understand what we see, and there'll be a lot more to come in the weeks ahead. Okay, then we'll have to check back, either with you or one of your colleagues. We continue to learn an awful lot about the rings. Are the special conditions during the equinox likely to help us learn even more about these fantastic structures? Oh, absolutely. With the conditions at equinox, with the sun essentially edge on with respect to the rings, we have a chance to look for and get a three-dimensional view of the rings.

Anything like warping in the rings or anything with vertical structure would cast shadows. In fact, it's just been fascinating to watch as the shadows of the moons and the tiny moons outside the rings grew longer and longer and started to go across the rings. And in fact, pretty early on, we made a very interesting find in that there's a gap called the Keeler Gap in the outer part of the A-ring, and there's a tiny moon Daphnis inside. Daphnis is only about five miles across, and it's keeping this 26-mile-wide gap open. Its orbit is slightly inclined, and so what we saw as Equinox drew near is that Daphnis

is actually pulling material above and below the ring. So along the edges of the rings, there are these structures. They're anywhere from a third to one mile high, which is more than 150 times more than the thickness of the rings, which you think is only something like 30 feet. So here are these huge structures going up, towering structures casting these beautiful shadows with Daphnis sitting in the center, kind of having the prime seat.

So sort of proof of concept that, yes, any additional vertical structures. We also saw an object in the B ring large enough to cast a shadow. And so we're continuing to look through the images and see what other interesting finds might be there with this unique geometry. It's unique. It only happens once every 15 years. And so we're just very lucky to have Cassini at Saturn for this time of equinox. And for this particular equinox, it turns out that Saturn was very close to the sun. And so it really wasn't possible to do much in the way of ground-based observations

because you wouldn't want to point your telescopes so close to the sun to look at Saturn. Yeah, not even the Hubble. Right. Cassini had a ringside seat, you could definitely say. You could. You could. Better you than me. Our model of these rings seems to be becoming more and more complex the more we learn about them. Oh, absolutely. Yes, the rings have gone from our ideas that they were single individual particles floating around to now the fact that they clump together and create these structures that we call gravitational wakes. And we're starting to think now, and have been thinking, that rings are an excellent model for planetary disks, similar to what formed our solar system.

And so as we learn more about the processes happening in the rings, that's a really good analogy for processes that probably occurred within our own disk from which we got the planets, including the Earth. And are probably, well, we in fact we know now, are continuing all across our galaxy and probably the universe. Right, right. That's true. Other planetary disks as well. So what we're learning here at Saturn's rings will help us perhaps understand planetary formation elsewhere in our own galaxy. You know, someday, and maybe people are already saying, this may prove to be one of the most

important findings, conclusions that Cassini helps us reach based on the data it collects out there at Saturn. Right, and I think there's still a lot more to learn. Certainly, every time we get a unique geometry, we learn more and more about these fascinating rings. And they change over time, don't they? I mean, they evolve. Right. In fact, the F ring in particular, we've seen a lot of change happening within Saturn's F ring, a narrow ring that's just outside the main rings. We've seen clumps come and go, jets, streamers. We're coming up toward the end of this year in a very interesting occurrence where

the moon Prometheus, which is just orbiting just inside the F ring, will be at its apoaps, Prometheus, which is orbiting just inside the F-ring, will be at its apoaps, where the F-ring is at periaps. So we'll see lots of activity as Prometheus continues to distort and actually sort of start to dip into the F-ring. And give us definitions of those terms, please. The apoaps of an orbit is the furthest. If an orbit is sort of egg-shaped or elliptical, apoaps is the point where you're the furthest in your orbit from Saturn.

And if you're at periaps, that's when you're the closest to the planet. So if you get this anti-alignment, you can get Prometheus then at its closest point to the F ring. All right, let's go a little farther out now and consider those moons, which are no less fascinating than what's going on with the rings. We'll get to Titan maybe in a minute, but since we last spoke, even more fascinating and very exciting data spewing out almost literally from Enceladus. Right, right. Yes, as we're getting a chance to try and understand the data in more detail, a couple of very interesting findings.

One of those was the detection of sodium salts, essentially the equivalent of table salt and baking soda, and some of the tiny particles that are in the E-ring, which of course are coming from Enceladus' plumes. And these particles are almost pure water ice, but the Cosmic Dust Analyzer is also able to pick up, trace hints of these salts. And why salt is so important is it tells us that it's strong evidence for a liquid source for the plumes, perhaps even a liquid ocean underneath them. And so the detection of sodium is very important in that way in saying that the source is possibly a liquid. And the other very interesting find was the detection of ammonia,

a liquid. And the other very interesting find was the detection of ammonia that the ion and neutral mass spectrometer basically was on during our flyby through the plumes. It could sniff out the chemicals that were part of the plumes and they found organics, water, of course, and then strong evidence for ammonia. And you might say, well, why is ammonia, you know, so interesting? And in part, what it is is ammonia dissolves in water, and it acts as a really great antifreeze. And so you can, with ammonia in the water, it can be in a liquid state down to something like minus 143 degrees Fahrenheit. And so that tells us that another piece of evidence

that that source for the plumes could be liquid water. More from Cassini Deputy Project Scientist Linda Spilker in a minute. This is Planetary Radio. Hey, hey, Bill Nye the Science Guy here. I hope you're enjoying Planetary Radio. We put a lot of work into this show and all our other great Planetary Society projects. I've been a member since the disco era. Now I'm the Society's Vice President.

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That's planetary.org slash radio. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. Linda Spilker of the Cassini-Equinox mission is giving us another update on what that spacecraft has taught us about the Saturnian system, including Enceladus, the moon that shoots towering water geysers out into space. Is it getting easier to understand how this little moon that everybody thought was too small for any of this could have all this wet activity?

It's still a puzzle how a moon this size, that's so small that we think should have been frozen solid by now, could have this much activity going on. The process by which it have this much activity going on. The process by which it got started and keeps going is something that we're still trying to figure out. And we hope as we get more close flybys, we have a couple of more dives into the plume in November that perhaps will get more pieces to this puzzle that's in Celadus. Let's turn now to Titan. I'm sorry to say that I can't remember who I'm getting this quote from, but somebody just recently I heard call Titan,

at least geologically, the most similar body to our own, to Earth in our solar system. Do you agree? Yes, it's similar in the sense that Titan is one of the few places where you have a liquid. In this case, it's liquid methane or like the gas in your stove that can be a liquid, a solid, and a gas. And so it works on the same way on Titan's surface as water does here on the Earth. So you can form methane clouds. They can rain out. They fill lakes on Titan, create river channels, and very, very similar to the processes we see, the erosional processes we see on the

Earth. So the temperatures are quite different. It's very much colder on Titan, but many of the processes between Titan and the Earth are very similar. It's so fascinating that all of these phenomena can be so similar, and yet they're offset by hundreds of temperature degrees just working with a different fluid, and to the point where the similarities now apparently even extend to storms. Right, right. In fact, a recent paper came out that there was a huge storm. It actually was back in April of 2008, detected from the ground. It turned out that this storm formed and dissipated between two of Cassini's

close flybys of Titan. And this storm was in the dry equatorial region, and it's fascinating because, first of all, it was a large storm, which they don't appear to happen too often, and then second, to have something in these dry latitudes, you'd need some process to raise the humidity of methane. In other words, some injection of methane into the atmosphere, perhaps. Maybe a cryovolcano, so you have both heat and the methane coming out to create this huge convective cloud, this convective storm that sprang up near the equatorial region

on Titan, or it could be something else that we haven't even thought of yet. So it was very exciting to see this cloud. And in fact, given the rare occurrence of clouds with Cassini, we've made a change in our program. We're now trying once or twice a week to go back and take some pictures of Titan just because it can be a very long time between our close flybys with Cassini. And we want to make sure not to miss anything. Okay, so what's next other than these results to look forward to from Cassini's studies during the equinox period? Well, we have a couple of close Enceladus flybys coming up in November,

and so that'll be very exciting. And we continue to have additional Titan flybys every two or three weeks or so. And so it'll be interesting to see if we see any more cloud activity or changes in the weather now that we've passed through equinox. And as the sun starts to shine at the north pole of Titan, that's the place where we've seen all of these methane lakes with ethane inside of them. And will these lakes start to evaporate, perhaps, as the sun starts shining more and more at the north pole? And will we see perhaps more weather as the seasons change on Titan? Any of those upcoming Enceladus flybys going to be those very low ones,

possibly right through those plumes? Yes, that's the plan. It's basically to skim through those plumes and continue to make measurements about their composition. Just one more. How about down there on the big planet? Is anybody watching for changes in, for lack of a better term, the weather as the planet also passes through the equinox. Yeah, for looking at Saturn, this is a great time because with the sun essentially edged on with the rings,

as you can imagine, the rings cast their smallest shadow ever on Saturn. And so you have a great view of both the northern and southern hemispheres of Saturn. And so it'll be a good chance to observe the clouds and the weather on the planet as well. Linda, it's always a pleasure, especially when you make the trip in in spite of the fact that one of those famous L.A. brush fires is burning right there in the hills above JPL. Right. Yeah, the La Cunada fire, I was keeping an eye on as I came in today, and I could see these great large clouds of smoke coming up. And fortunately, it looks like the wind's sort of blowing north,

so it's not blowing the smoke in the direction of JPL. Okay, we don't want any interruption in data collecting for Cassini or any of the other missions there at JPL, and still figuring out how to get spirit out of that sand trap, too. So hang in there, and good luck to all of you on the Cassini mission, and I look forward to checking back with you again. Okay, great. Thanks a lot, Matt. Linda Spilker is the Deputy Project Scientist on the Cassini mission.

She's been with that mission for, oh, I think since she was about eight years old, right, Linda? No, not quite, but for a long time, since well before launch. Anyway, it is Cassini, and it is the Equinox mission now, of course, the extended mission of that great spacecraft that continues to explore that amazing Saturnian system right in our own backyard, right here in the solar system. We'll take another look at that solar system and beyond when Bruce Betts is visiting with us for this week's edition of What's Up. That's after we hear from Emily.

Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, how could an asteroid make such a big mark on Jupiter when it doesn't have a solid surface to make a crater in? When a small object smashed into Jupiter on July 19, 2009, it left a dark mark near the giant planet's south pole. The mark was the size of Earth, yet the object that hit Jupiter was likely only around a kilometer across. How could such a tiny body make a big mark in a gassy planet? To understand the answer, you need to know what happens when an asteroid comes in for a crash.

First of all, it arrives at an incredibly high speed, about 100 kilometers a second. The impact speed is much faster for Jupiter than for Earth, because Jupiter's gargantuan gravity accelerates incoming bodies to much higher speeds. As the rock rockets downward, it compresses the gas in front of it. Just as a bicycle pump heats when you use it to compress Earth's air, the air in front of the asteroid heats, but because the speed is so high, the pressure is enormous and the air heats to thousands of degrees. Soon, the rock explodes. It vaporizes, contributing its elements to Jupiter's clouds, but the huge planet hardly notices that. What it does notice is the splash. Fiery hot gases fly in all directions from the impact, especially upward through the

transient hole left in the atmosphere by the incoming fireball. This rebound brings up copious amounts of ammonia from deeper in the planet, which is responsible in part for the dark color of the impact mark. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. We're into What's Up on Planetary Radio. We're with Bruce Betts at the other end of the Skype line. And that other end is uncomfortably close to the big fire in the San Gabriel Mountains, which you probably have seen on the news if you're listening to this early in the week.

What's going on there, big guy? Well, we're, sorry I'm distracted because it's the first big wind. That's the one thing we haven't had. Now there's a big wind blowing. Yeah, I hear that. I hear that. It just picked up. What's going on? What do you see? Well, I'm looking out the backyard and probably about a mile and a half, two miles away, the mountainside is on fire and there's huge columns of smoke, and we've got several helicopters that are taking turns coming in and doing water drops on the fire line. It's been going for about three days, and this is by far the closest it's been to me personally. Wow.

It's obviously getting close all over the place. I think it's 35,000, 40,000 acres now. Are you in any danger of having to evacuate? If you phrase it that generally, yes. Probably no. On the other hand, you know, a mile away is evacuated out. So it's always possible. It's certainly still getting closer. It's not beaten down. How's the air there? Most of the time, it's not too bad. This morning, the wind did, something had changed. So it was very smoky. But most of the time it's not too bad. This morning the wind did, something had changed, so it was very smoky, but most of the time it's been blowing up and blowing off in other directions,

making life miserable smoke-wise for other people. Wow. All right, well, take care of yourself there, and we won't keep you at this for too long, but I bet you, because I've seen that smoke plume from my area, which is 30, 35 miles away, and it is humongous. I bet it can be seen from space without any problem at all. Oh, I'm sure. Hopefully NASA, they often release pictures of fires from space, and this has, I'm sure, been very, very, very visible. Well, would you like to tell us about the night sky,

or would you just like to run out of there as fast as you can? For now, I'll tell us about the night sky, or would you just like to run out of there as fast as you can? For now, I'll tell you about the night sky. Hopefully, people aren't too disturbed at getting a fire report instead of a sky report. But I'm going to tie it all together. It's all going to come together. But first, let's tell you what you can see in the night sky. I can see a Sikorsky sky crane, but most of you in the night sky will be able to see Jupiter very bright in the east in the early evening, high overhead in the middle of the night. Venus in the pre-dawn looking extremely bright off in the east.

What was that? We'll say it was a giant fire engine, but I think it was a bus. Okay. I was looking the other way. We got in the pre-dawn sky, ooh, there's a water drop. We've got a water drop. We've got Venus looking extremely bright in the east, and up above it, Mars looking dim and reddish.

In a few weeks, I'll have all sorts more and all sorts of planets coming up in the pre-dawn, but that's what we've got right now. Let's go on to this week in space history. what we've got right now. Let's go on to this week in space history. 1979, Pioneer 11 became the first spacecraft to fly past Saturn. Kind of cool. Yeah, very cool. On to random space. Ah! A little ember fly down your shirt there or something? A little ember fly down your shirt there or something? Okay, we're good. Hey, did you know, I mean, I know you did, but let's make sure people know,

Earth, it's the only planet, at least in our solar system, with a significant amount of gaseous molecular oxygen. That's stuff that makes it so fun to breathe and possible. And what fuels these fires. Can't have these fires on any of the other planets due to lack of oxygen, but on the other hand, you also can't breathe. You did promise to tie it all together for us, so thank you. I did, and I do have to mention the key difference, amazingly to me, every time I think about it, life.

It's life that's put all this, not all, but most of the oxygen into the atmosphere. Yeah. We have a really special trivia contest. It's not a trivia contest this time. Tell us about it. We asked you if you were on Twitter or the equivalent and you're tweeting to aliens, sending a signal out to them, but keeping it short like a tweet, what would you say? And we said we would judge it purely upon the how much it made us laugh. How'd we do, Matt? I know how we did. We did well. Tell us more. Yeah, we really did. We did. Some really nice responses. And can I just read some of them to you and we'll build up to our winner? Please do.

Alright, here goes. From John Gordon. Remember, it's got to be fewer than 140 characters and everybody did an admirable job of that. Here's his. Help! We've fallen and can't get up. Which, for those of you from outside the U.S., that was the punchline to a TV commercial here for a long time. Okay, here's one from Edward, our friend Ed Lupin down in San Diego. If you're waiting for better, I'm sorry, but I Love Lucy is as good as it's going to get. If you're waiting for better, I'm sorry, but I Love Lucy is as good as it's going to get.

Message to those tall blue women of the nearby exoplanet, how you doing? How you doing? How you doing? And the very similar from Susan Noe, hey, baby, what are you wearing? And how many arm holes does it have? Good question. Here's what could be your favorite. I'm not sure.

You'll have to tell me. Are you ready? This is from Dwayne Jones. We are in no need of your physiologically advanced technology. Although odd, Bruce Betts singing random space facts is normal here on Earth. Why, yes, that's brilliant. That deserves special mention. But you know what?

Our winner, who came up with six or seven of these, we're only going to read three. But I think maybe I'll put some of the rest in my Twitter account. It's Matt underscore Kaplan, just so that people can see some of those. But here are three from Torsten Zimmer. If you're working on your abduction schedule, I'd like to send you a list of politicians you might consider. And then this one, Dear Aliens, you are probably completely different from us. Congratulations.

And then here, and I think this is your favorite, and I love it too. Here it is. Dear Aliens, is it true you taste a little bit like chicken? and I think this is your favorite and I love it too. Here it is. Dear aliens, is it true you taste a little bit like chicken? None of this defensive posture. Let's find out. I love it.

I've been reading that for a week or two. All right, so Torsten, we're going to send you a Planetary Radio t-shirt and an Oceanside Photo and Telescope rewards card and anything else that's laying around the office, okay? How's that? And to the rest of you and all of you who we didn't have time to read your tweets, thank you so much. You guys are a laugh riot. You keep us entertained even when the fire is coming over the mountain.

Yes, thank you. Let's go on to the next trivia contest, and for some reason this one's in my mind. What is the ballpark surface temperature on Venus? Because I think we've hit it. And you're part of town, yeah. Yeah. Well, okay, that sounds good to me. You've got until Monday, September 7, at 2 p.m. Pacific time, to get us that answer.

What did you say, the ambient or the average temperature on the surface of Venus? I use the highly technical term ballpark. Yes. In other words, the approximate surface temperature. It does vary, but it doesn't vary nearly as much as on other planets. So just go to planetary.org slash radio, find out how to enter. We better get out of here. I hear another one of those helicopters coming over, and you might be getting a shower.

Did you make a call? I have connections. I'm sorry. I should have gone up to the fire line to get better sound for you. I apologize. No, you stay away from the fire line. I thought I'd at least get a sky crane to fly over. Maybe next time, but

hopefully not. Alright, everybody, go out there, look up at the night sky, and think about really accurate drops of large quantities of water and fire retardant. Thank you, and good night. I will think about that, and we will wish you the best there, Bruce. Hope everything goes well, and this thing is

under control very soon. He's Bruce Betts, the Director of Projects for the Planetary Society. He joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Keep looking up. Thank you.