Planetary Radio: Space Exploration, Astronomy and Science - Bill McKinnon and Ices and Seas in the Outer Solar System

Episode Date: August 20, 2007

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Mysterious moons of ice and sea, 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. Last week's Boulder, Colorado workshop was officially titled, Ices, Oceans, and Fire, Satellites of the Outer Solar System. Planetary scientist Bill McKinnon was in the thick of it. He'll help us explore Europa, Enceladus, and Titan, three bodies that dominated many of the sessions. Bruce Betts also checks in from the road. Our man reports from SpaceFest in Mesa, Arizona, where it was almost too hot to go outside for a look at a very busy night sky.

I say almost. And Emily Lakdawalla will answer another of your questions about space exploration, this time focusing on what may be the universe's most exotic rocket fuel. The space shuttle heads home a day early. That story moved as we were polishing off this week's show. It was just a couple of days after NASA determined no repairs were necessary for the damage to Endeavour's underside caused by foam or ice from the external tank. So why the rush? The space agency is worried that Hurricane Dean could force the shutdown of mission control in Houston. It wants the astronauts safely on the ground before

that can happen. It was a busy mission, delivery of tons of cargo, four spacewalks, installation of a new truss and a gyroscope, and more student interaction than usual, not surprising with teacher Barbara Morgan on board. I bet you never thought you'd see a giant star that looks like a comet. Check out the image of Mira taken by the Galaxy Evolution Explorer. That tail is 14 light-years long and growing. There's coverage at planetary.org. It's Emily's turn. I'll be back with Bill McKinnon in a minute. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, the xenon propellant for Dawn causes problems when the spacecraft spins up or spins down.

Why didn't they store it as a solid or use baffles in the tank? Answering this question requires some background. The Dawn spacecraft will travel to asteroids Ceres and Vesta using the power of ion propulsion. The 400 kilograms of xenon propellant that launch with Dawn are stored in a 300-liter tank in a supercritical state, in which it behaves like a gas but has the density of a liquid. When dawn launches, it spins up to nearly one rotation per second before firing its third stage thruster. Once on its way to the asteroid belt, it'll spin back down to zero. But because there are no baffles in the tank, the xenon will keep spinning. Friction will eventually slow down the spinning xenon,

but not before it imparts some spin to the spacecraft. How much spin won't be known until it actually happens. Why didn't Dawn's engineers avoid this by storing the xenon as a solid or baffling the tank? Stay tuned to Planetary Radio to find out. Bill McKinnon's career was getting underway as the Voyager spacecraft gave us our first close-up looks at the amazing moons of Jupiter and Saturn. Thirty years later, these bodies still fascinate him and a growing community of planetary scientists.

That community gathered in Boulder for three days last week at a conference sponsored by NASA and the Lunar and Planetary Institute. We spoke just after the workshop and before Bill returned to Washington University in St. Louis, Missouri. That's where he is professor of Earth and Planetary Sciences, conducting research on the geophysics and dynamics of these incredibly diverse bodies. Bill McKinnon, thank you very much for joining us, especially at the close of this conference, which probably will dominate our conversation today, or at least the topics that were covered at the conference will dominate our conversation. Could you tell us a little bit about this meeting

that just completed? The title is very evocative. It's called Ices, Oceans, and Fire, Satellites of the Outer Solar System. And it's a gathering of the Klan, basically, of people who are interested, not in Scottish heather, but in fact the icy moons of the distant planets. It's a really interesting group of people, some of whom have been working in the field since the 1960s,

since the beginning of the space age, and some who are, you know, just entering graduate school, and I just find this fascinating. And it's really our first meeting in over 20 years in which everybody has come together to talk to each other about everything that we've been learning in the last few years with these especially capable missions, the Galileo mission, which is now complete, Jupiter, and the ongoing Cassini mission at Saturn. And I think we've come up over the rise, and we can sort of almost see the promised land of a sort of integrated understanding of what's going on out there. I should say, in 20 years, I mean, really, there has been a revolution in our understanding of these little worlds.

It's been mind-boggling. I mean, it's perhaps three steps. You know, first, there's just the slow, painstaking gathering of knowledge through telescopes. And that's when I talk about people who were working in the 60s. through telescopes. And that's when I talk about people who were working in the 60s. It's the Voyager missions in the late 1970s into the 1980s that revealed the outer solar system and its diversity and beauty. But they just went so far with the technology that was basically available 35 years ago. But these new missions have just blown the doors off, you know, the vaults of all the information we could hope to have.

And so we are in the midst of a discovery and synthesis phase such as I've never seen. It's just very exciting, and it's very cross-cutting. And it's, you know, each of the big planets of the outer solar system has a number of moons, some of which are very large. And, of course, there are even more moons, if you really want to think about it, out beyond Neptune and the Kuiper Belt. Pluto and all the other bodies of the Kuiper Belt, many of them have moons, maybe most of them. Someone, for all I know it was you, I can't remember who this quote came from,

For all I know, it was you, I can't remember who this quote came from, said that, who knows, we may learn that the preponderance of bodies like these in the solar system, well, are exactly like these, that they may be icy bodies. I think we're probably happy with the idea that by mass, the most important bodies in the solar system are the gas giants. But in terms of the solid worlds, there are an almost uncountable number of these icy worlds out beyond Neptune. I mean, because they stretch through the Kuiper Belt and on all the way, as far as we can tell, to the Oort Cloud, which circles at a great distance from the sun. I suppose, so where they lose out in mass, they probably make up somewhat in numerical values. Yeah, they don't. If you had your choice of any of these bodies in our solar system now, where would you go? I personally, if I had to pick any one thing,

given that we have a highly capable machine already working at Saturn, I would send one back to Jupiter to finish the job that Galileo started. Because as wonderful as Galileo was, it did have a broken antenna. And there's a lot more data, a lot more landscape to survey. And there's this moon, Europa, which we're pretty sure, from the data we have, has an ocean underneath its ice shelf. It's the one place, I think it's one of the key places in the solar system to really test the ideas about how life may form and evolve. To my mind, as hard as this question is to answer, it's maybe the paramount question, you know, in a geologic setting, how life

starts. Given, well, let's say, given a relatively unconstrained amount of money, one could orbit Europa, one could land on Europa, one could drop sufficient sensing stations to, you know, basically see through the ice shell. And of course, in the future, when we have truly unlimited funds, we may be able to go through that ice shell. And of course, in the future, when we have truly unlimited funds, we may be able to go through that ice shell once we've surveyed it, found thin spots or whatnot, and send autonomous robotic vehicles into the ocean to find out what's down there. If my research is correct, some of the work that you've been part of is on the convection of ice on a body like Europa, which has suggested to some people that we might, obviously it'd be lovely to have advice that would melt down into that ocean, but that we might find

some very interesting things right there on the surface that used to be underneath. Yeah, I think if you look at the surface of Europa specifically, you see areas that have been clearly broken up in a manner that we simply call chaos. It's a geological term, but I think it's evocative enough. And we see that these materials are broken up. We see that they're discolored with materials that we don't actually understand the composition of. And that's another thing we could actually measure either through their spectral identifications or by going directly to the material. There's particular places that look particularly fresh in terms of potential eruption of ocean water.

And we didn't see those areas well enough with Galileo to say any more about it. I'd really like to go back to those places. And I don't really want to sell the other amazing places in the solar system short, which include Titan around Saturn and the volcanically venting moon Enceladus. I mean, I could talk equally as enthusiastically about those two as targets. But right now we do have a machine that is carrying out a program of exploration of Titan and Enceladus. You called Enceladus a geologist's paradise,

and we've heard on this program that not too far into 2008, Cassini may actually get incredibly close to that moon. That's the plan. Cassini is moving into its so-called extended mission phase. That is, the official mission, as funded funded by NASA will end, but then they get permission because the machine is in such robust health and there's such reserves of power and maneuvering fuels that they can just continue on for several more years. They just sort of need, you know, just the incremental amount. And so this extended mission has been approved and

pretty much designed, and it will focus a lot on both Enceladus and Titan. We'll hear much more from Bill McKinnon about Enceladus and still mysterious Titan after a break. This is Planetary Radio. 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. And you may well ask, why do we go to all this trouble? Simple. We believe in the PB&J, the passion, beauty, and joy of space exploration. You probably do too, or you wouldn't be listening. Of course, you can do more than just listen. You can become part of the action, helping us fly solar sails, discover new

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Bill McKinnon is a leader in the community of planetary scientists who study the moons of the outer solar system, especially the icy ones that are beginning to reveal seas of water or colder fluids. The professor of earth and planetary sciences at Washington University in St. Louis had just begun to talk about little Enceladus circling Saturn. I imagine a lot of people listening to this would already know a lot about Enceladus, but what's really keen about Enceladus, but what's really keen about Enceladus was brought out in this meeting in particular is we are looking at it in a way we haven't really been able to look at other satellites or even bodies in much of the solar system before because the Cassini mission has such an interesting and complementary suite of

instruments. So we're not just going there and taking pictures, or we're not even just going there and taking spectral images. We are measuring the heat flow that's coming out of the body. We've never been able to do that remotely for an icy world. In fact, we don't even know what the heat flow is out of Mars, but we know what it is out of Enceladus. And because Enceladus is volcanically venting into space, we can fly through the plume and measure the composition of this material, this gas and particles. It's an unprecedented constraint on what's going on down there. So we're looking at a world that's tortured by tidal stresses, is internally heated despite its rather diminutive size. It's only, you know, 500 kilometers across, 300 miles. There's a huge polar hotspot of infrared emission

and what appear to be very active and young tectonics. You cannot see an impact crater in this sort of area around the South Pole. What's going to happen in 2008 is that the Cassini spacecraft is going to come very close, get very good images, very good thermal data, and go deeper into the plume than has ever been attempted. In fact, the only real debate is how low do you go? How close to this, because you're speeding through it at several kilometers a second, how close to this plume gas and these tiny micron-sized particles?

They'd be invisible to us if they were floating in front of our eyes, but you put a giant cloud in space, you get enough reflected light or scattered light. But it's still a question of how safe is it for the spacecraft. So it's a kind of remarkable 21st century way of interrogating, if you like, you know, a world and trying to understand it. One of the things I said at the meeting was I'd love to take the Cassini spacecraft with all its sort of new modern capabilities and send it back to Jupiter when it was done at Saturn. Of course, it'll never really be done at Saturn, but it's that kind of sort of scientific adventure that I think is driving us all forward. We're all very hopeful, following on to Cassini,

that NASA will have the resources to mount another mission of that class to one of these compelling targets, whether it's Europa Enceladus or Titan, circa the year 2020 at this point. Any revelations about Titan at this meeting that just closed? I think we're still in the data gathering phase. Titan remains the true enigma of the Saturn system in the sense that you can never quite see the surface clearly enough or never see enough of it. It has a thick atmosphere with a lot of basically smog and clouds. And so the visible and even near-inf near infrared images are tantalizing but fuzzy.

Where we really learned about Titan is by, again, a complementary series of measurements, these radar images. And of course, the Huygens probe in January of 2005 went down to the surface at one point, but as it went down, it took a lot of pictures, and you sort of got the gondoliers or the biplane view of what flying around in Titan might look like. So there's a bit of ground truth and a bit of sort of close-up imagery. And we don't have a complete picture of Titan the way we do of Venus, because instead of circling and orbiting Titan, we've had to build up one strip or noodle at a time, and they crisscross in places. And it's taken time to figure out that the things that look dark in the visible images

were actually not seas of liquid ethane, let's say, but in fact were seas of sand, dark sand-sized particles, which themselves may be organic in nature, but they turn out to be great longitudinal dune seas. And that was by actually comparing visible and radar images. And since people have long predicted, at least the theorists have long predicted, that there's a reservoir, a liquid reservoir, an ocean or a sea or some sort of liquid reservoir on Titan, well, where is it? And indeed, it turns out to be at the poles of both

worlds. And we only have radar at the North Pole, but it's finding these amazingly lake-like things. The final proof of the lakes would have to come from something like altimetry, that is, height data. You would expect a sort of super uniform level surface. And that experiment hasn't been run yet. But the reflectivity of these things is extremely dark. And you've probably seen these pictures, and you see from a landscape, from a process point of view, it's mind-bogglingly similar to the Earth. landscape with an integrated drainage of, you know, river, streams into rivers, into larger rivers and channels, all moving down to various lake-like bodies, which have very crinulated and corrugated edges. Got to be supremely exciting to a planetary geologist.

Yes, yes. It's a whole new, it's the most Earth-like terrain anywhere else in the solar system, much more Earth-like than Mars. Mars may have looked like that at one point, four billion years ago, but it's been a dry world for a long time, and there's been a lot of erosion and infilling, and so we see the traces of the riverbeds. On Titan, it's clearly an active process. In fact, one of the things that came out of the meeting is that, given the amounts of, they think, ethane mist that's coming out of the atmosphere, it seems that the drainage that you see can't have been caused by the very slow trickling of liquid from the sky there and that there must be room for heavier precipitation events or downpours, like here in the desert southwest where I am right now,

where you dry most of the time, but then you get these great rainstorms and the washes fill with huge floods of water. Titan, of course, it wouldn't be water. It would be something more exotic, ethane and methane in the solution. So much to explore right in our own backyard. We're just about out of time. You talked about this community, or clan as you called it, of scientists who study these outer worlds in our solar system, icy satellites.

I'm sure you see it as a time of increasing excitement in this community. I wonder if it is attracting more and more colleagues. Well, yes. It's just the quality and amount of data that have been returned both by Galileo and are being returned by Cassini attract a natural curiosity, especially, I think, of young people because it's like when they find out this stuff, they say, this is the most amazing thing they've ever seen. I mean, in a sense, we've explored places like the moon and Mars so long that they've become somewhat familiar. You know, they're so Earth-like in a way that

people say, well, that's wonderful, but I want something truly amazing. And I think when you see these radar images of the lakes of the North Pole of Titan, this is truly amazing. I see that in the eyes and in the attitudes of the people in graduate school. That's very encouraging. And we will keep our fingers crossed for that return mission to Jupiter and in particular to Europa. And or wherever it goes.

I think we'll all be pleased. Thanks, Bill. Very much. Professor Bill McKinnon teaches at Washington University in St. Louis, Missouri, where he conducts research in the McDonnell Center for the Space Sciences. Emily is back with more on that strangest of rocket fuels. Then it's Bruce Betts for an on-the-road edition of What's Up. I'm Emily Lakdawalla, back with Q&A. 400 kilos of supercritical xenon in Dawn's tank is going to keep on spinning after Dawn's launch sequence is over, giving an unknown amount of spin to the spacecraft before it finally sloshes to a stop. Dawn's engineers couldn't have gotten around this problem by storing the xenon in the solid state because solid xenon requires very low temperatures.

Not only would it be hard to keep the xenon at those temperatures, but Dawn's electronics would have to be insulated from the freezing cold xenon. A more obvious solution to the spin problem would be to build flat plates called baffles into the tank, which would prevent the liquid from spinning differently from the spacecraft. Why isn't the tank baffled? From the beginning, engineers recognized that the xenon tank would be one of the most difficult design problems facing the mission, so work started on the tank long before most of the rest of the spacecraft was designed. By the time they figured out that the

complete system, spacecraft and the launch vehicle, would produce this particular problem, it was too late to design baffles into the tank. Instead, Dawn will simply have to wait eight minutes after launch for the xenon to stop spinning, then use up some precious chemical thruster power to counteract whatever amount of spin the spinning fuel gave to it. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio.

Bruce Betts is on the phone this week. He's at something called Space Fest in what, Phoenix? Indeed, or roughly Mesa, Arizona. And it's hot here, like really, really, really hot here. And this is from someone who grew up in Sacramento. Yeah, it's fortunately air-conditioned inside, but it's 110 outside. Well, stay indoors. Are you there with a lot of space nuts?

With a lot of space what? Nuts. Well, I don't want to go on the public record of stating it that way, but there are a lot of space enthusiasts here. Yeah, I am. It's neat. It's put on by Kim and Sally Poore of Nova Space. It's got a combination of people like me talking about space issues.

They've got space art displays, some other booths, and they have a bigger collection of astronauts than I've ever seen in one place. I'm hanging out a few feet from Buzz, and we've also got Ed Mitchell and Dave Scott, and even Scott Carpenter from the original Mercury 7. Wow. Alan Bean, Rusty Schwe Carpenter from the original Mercury 7. Wow. Alan Bean, Rusty Schweikert, the list just goes on. You were speaking not too long ago. I was, which, of course, is the highlight of the conference,

kind of a letdown to go to the Apollo astronauts. But yes, I spoke about the glories of Planet Earth-19 projects, introducing people to work with Phoenix, with the upcoming Phobos mission of the Russians, a variety of other wonderful, wonderful things. Well, for those of us who can't be there with you, give us a taste of the night sky at least. Well, the night sky that you'll be able to see, even not from here. We've got, of course, the total lunar eclipse coming up on the night of August 27th or 28th,

depending on your time zone. You will be able to see that if you are in Eastern Asia, Australia, the Pacific Ocean, or the Americas. So we'll get a chance to see it, although it will be beyond the middle of the night for us to see it. We'll give you a link to the NASA eclipse site where you can get all the details. Partial solar eclipse, September 11th, same deal, but limited to basically South America. And if you listen to this shortly after it's posted, you can catch the moon right next to Jupiter on August 21st in the night sky. And even if you don't look then, you can see Jupiter looking like the brightest satellite object in the evening sky. Hard to miss it. We'll be up there in the object in the evening sky. Hard to miss it.

We'll be up there in the south in the early evening. And Mars coming up around the middle of the night in the east looking dim and reddish. So that's what our night sky holds. Moving on to random space. Did anybody look? Yeah, they did. But, you know, even toned down. I should have just screamed it out, the glory of the random space plane.

Hey, in honor of the Apollo guys here, did you know the command module pilots, those who would be alone traveling around the moon while the other two went down to the lunar surface, they were out of radio contact for 48 minutes of every orbit and truly became the only person on the other side of the moon. Now there's a distinction. There's something for Mike Collins and his crowd to be proud of. Yeah, it's kind of profound. The rest of humanity was on the other side of the moon from them. And let's go on to trivia. So we asked you, what is the only moon in our solar system known to have an intrinsic magnetic field?

In other words, one actually generated inside of the moon by some process as opposed to induced magnetic fields that you can find in a few moons that have liquid, salty liquid water or something like that underneath inside a strong magnetic field like Jupiter. But one of them we know to have its own induced magnetic field. How do we do, Matt? Well, there were a fair number of guesses on this one, but most people did get it right. And I guess the correct answer is Ganymede. Indeed, Ganymede, largest moon in the solar system, generates its own magnetic field, as discovered by the Galileo orbiter.

And it was our listener Rowena Cadiz. Rowena Cadiz of Chicago, Illinois. First-time winner, as far as I can tell, who got chosen by Random.org. And will be receiving a Planetary Radio t-shirt. Congratulations, Rowena. Congratulations. And if you'd like to receive your own, answer the following questions and hope to be randomly selected. Again, we'll keep the Apollo theme, since I'm just oozing with Apollo excitement.

Which Apollo was hit by lightning? Which Apollo rocket was hit by lightning shortly after liftoff? Go to planetary.org slash radio and find out how to get us your entry. When do they need to get that in by, Matt? I think they better get it to us by the 27th of August, Monday, the 27th at 2 p.m. Pacific time. Any other questions? You say you're standing there next to Buzz, I guess? He's 10 feet away, yeah.

He's sitting in the booth with Charlie Duke. What are they doing, signing autographs? They are indeed. It's FanFest for astronauts here, and even some test pilots as well. So people actually pay to get autographs. pilots as well. So people actually pay to get autographs. And I've actually set up my own booth, and I'm actually paying people to let me sign autographs for them. I think I've cornered the market as the only person with a negative price structure. All right. Well, I certainly hope you can turn that to your advantage. And I wish we were there with you. I wish you were too, Matt,

and everyone out there. All right, everybody, go out there, look up at the night sky, and think about fluffy ducks. Thank you, and good night. Yeah, you fuzzed out there. What did you say, fluffy ducks? Fluffy ducks? I'll pick a simpler word. I just haven't thought of what it is yet.

Sorry, I was so consent. Okay, I'll try again. All right, everybody, go out there, look up at the night sky, and think about stars. Huh? Isn't that thematic? I think that's wonderful, since you're surrounded by some of the biggest stars in space exploration, and the stars will be lovely there in Mesa, Arizona, tonight. Oh, it will, when it cools to 90 degrees Fahrenheit. All right, well, have fun, Bruce, and we'll talk to you hopefully in person next week. Bruce Betts is the Director of Projects for the Planetary Society,

and he does join us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week. Thank you.