Planetary Radio: Space Exploration, Astronomy and Science - Bob Pappalardo and the Mysteries of Europa

Episode Date: June 26, 2006

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The Man from Europa, 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. Bob Pappalardo is new to Southern California, but an old hand at figuring out the mysteries of Jupiter's moon Europa, I'm Matt Kaplan. Are you feeling lucky? Maybe this will be your week to win a Planetary Radio t-shirt from Bruce Betts. You'll hear Bruce's night sky highlights and a random space fact or two, even if we don't send you a new wardrobe. And you'll hear a few space headlines right this very minute. With the New Horizons spacecraft speeding toward its Pluto encounter,

that cold little planet, or whatever it is, now has official names for its two recently discovered moons. You can read all about Nix and Hydra at planetary.org. As we go to broadcast, Space Shuttle Discovery remains on target for a July 1 launch. By sometime next week, it could be docked at the International Space Station. September 2 or 3 of this year, depending on where you live. That's when the European Space Agency's Smart One lunar orbiter will have its encounter of the kerblui kind with the moon. We'll have special coverage when the end is nigh. And this podcast note, have you been picking us up via iTunes?

If so, it's time to re-subscribe to a newly revised link in the services podcast guide. Just type Planetary Radio into the iTunes search box and hit enter. We should pop right up and you won't have to miss one exciting nanosecond of the show. Oh, and we're now on more than 80 public radio stations, along with XM Public Radio. No brag, just the facts. Speaking of facts, here's Emily with a few from Iapetus. I'll be right back with Bob Pappalardo. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, could Iapetus's belly band have formed when the moon swept up one of Saturn's rings? Iapetus is an unusual moon in many respects.

Most famously, one hemisphere appears to be coated with very dark material, while the opposite hemisphere is bright and icy. The Cassini mission discovered another unusual fact, the presence of the belly band, a chain of mountains a thousand kilometers long and 20 kilometers high that lies exactly along Iapetus's equator. There's nothing like it anywhere else in the solar system, and planetary geologists have been at a loss to explain why and how it formed at such a position. The usual explanation for Iapetus's dark coating is that it came from outside Iapetus, so could a mountain chain have been built up if Iapetus collected all the material from one of Saturn's rings? Stay tuned to Planetary Radio to find out.

We first heard from Bob Pappalardo a few months ago when he spoke at an Ames Research Center conference on astrobiology. Now the expert on Jupiter's moon Europa is a neighbor of the Planetary Society. He dropped by for a conversation just a few days ago. Bob Pappalardo, first of all, thanks for joining us on Planetary Radio. Thank you. Pleasure to be here. Of course, you've been on before, but this is the first chance we've had to actually sit across from each other and have a conversation. It's something we've been wanting to do for a long time on the show. Also, welcome to Southern California,

now that you're a principal scientist on the staff at JPL. Sunny Southern California, having a great time here so far, really enjoying it. Haven't totally deserted University of Colorado, you said, though. No, I'm still adjunct there, and I still have two University of Colorado graduate students working with me now here at JPL. When we said that you were coming in today, one of the female staff members here said, oh, he's that cute Europan guy? Oh, no, my girlfriend's listening. I think it was just a casual bit of admiration there.

I said she could come out and swoon later. Oh, thank you. Just a casual bit of admiration there. I said she could come out and swoon later. Thank you. What, for you, makes Europa such a wonderful tourist destination in our solar system? Not just a tourist destination, scientific destination. Europa is an incredible place for so many reasons, but the chief one is astrobiology. A critical question in understanding our place in the universe is whether life is common or rare, as the planetary society is well aware.

Europa, we're pretty sure, say 90% sure or so, that there's an ocean beneath the surface of Europa, the icy surface. There's a chance that Europa has the chemical energy necessary for life. And so Europa is one of the key targets in understanding whether there might be other life in our solar system today, Mars, of course, being the other one. Now we have a large program that's sending spacecraft to Mars every couple of years. But as of the moment, we don't have a follow-up mission to Europa.

We're working on that. But the other thing besides the astrobiology, and we can talk more about that, is the geophysics. We don't get Europa yet. It's about the most complicated planetary situation that you could think of. It's ice, which has very complicated rheology, the way it flows and behaves. It's tidal interactions with Jupiter. It has resonances with its neighboring moons, Io and Ganymede. It's a complex system to understand. That complexity, that geophysical complexity,

is what also makes it astrobiologically interesting because there is tidal heating, which maintains liquid water below, and activity, which may pump chemical energy into the water and potentially allow for life there. While we were all extremely curious about that big ocean, the surface itself is so fascinating. It's so rich in features that I guess are still puzzling folks like you. Exactly. Again, we don't get it, and that's what keeps it interesting. Maybe I shouldn't say.

My favorite moon, if you ask me, is probably Ganymede, Europa's neighbor. We get Ganymede somewhat. We can look at Earth and look at Ganymede and go, okay, I kind of recognize how these types of features might form by extension of the icy crust over more mobile and flowing ice beneath. But we look at Europa and say, what the heck is that? It keeps us investigating. Europa is covered by these double ridges like a plate of spaghetti. look at Europa and say, what the heck is that, right? It keeps us investigating. Europa's

covered by these double ridges like a plate of spaghetti. They're overlapping one another. But you look at any individual one, and it's not just one ridge, but it's a pair of ridges traveling together across the surface. So what's made this sequence of ridges cross-cutting one another, and especially traveling across the surface in pairs like this. Well, one idea is that the surface has been pushed upward somehow, like a tree root growing beneath an asphalt sidewalk and warping it upward into a double ridge. But then, you know, there aren't trees growing there,

so what's underneath pushing up on the surface? And there are various models that involve the combination of water or warm ice to push up the surface and perhaps even to squeeze out on the surface. And then the other main type of feature on the surface is this model terrain, these freckles and spots. Some of the larger ones show evidence that ice plates have been mobile and moved around the surface and translated and rotated. And then there are competing models for that. Again, we don't really understand what's going on. One model says the surface has literally melted from below.

There's enough heat that some of these features are the result of melting, complete melting of the ice crust. Another model, and the one I tend to favor, is that the ice shell is thick enough that it actually convects, overturns like a lava lamp, where warm ice below is tidally heated, comes up toward the surface, colder ice sinks down. You usually don't think of solids flowing, but lava lamp is a nice analogy, or the inside of our planet, right? The earth is, is convict. Sure. Yeah. With, with warm pockets of rock moving up and

colder ones sinking down. So, so those are some of the models, but, but again, at, at meetings and through the scientific literature, there are debates going on. How did these things form? What does this mean for the interior? What does it mean for the plausibility of life or, for that matter, for where we might find life if we were to send a lander to Europa? In either of those models, though, that you mentioned, neither of which may be correct, but the best that we can come up with right now, it seems to say that just getting to the surface of Europa might allow us to get a good feel for what is way under that ice, since it's been rising up from below where the ocean is.

That's right. If the surface has literally melted, then it's easy. The surface has been in direct contact with the ocean. But even indirectly through this convection dredging material up from below, it may take hundreds of thousands of years for this stuff to get up from the bottom toward the top, but apparently it has done that, so there's probably been at least indirect communication. So yeah, getting to the surface someday and sampling the surface, or really just beneath the surface, will be critical in understanding Europa's

potential for life. And I say beneath the surface because that top 10 or tens of centimeters has been processed by charged particles which are coming in and hitting the surface and destroying any organic materials that might be there. Kind of like Mars, maybe. A little bit anyway. Reactive anyway. Mars, maybe. A little bit, anyway. More active, anyway. Yeah, exactly.

Mars, it's mostly ultraviolet light, whereas Europa bathed in the charged particle environment of Jupiter's magnetosphere, and there's no atmosphere to ward off, to stop charged particles from hitting the surface. More from Europa expert Bob Pappalardo when Planetary Radio returns in a minute. This is Buzz Aldrin.

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That's toll-free, 1-877-752-6387. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. Our guest is Bob Papalardo, who has just moved from the University of Colorado to his new position as a principal scientist at the Jet Propulsion Lab in Southern California. I'm assuming that one of the reasons you're happy to be at JPL now is because it may be a really good place for you to try and push this mission to Europa that you and so many people would like to see. Well, JPL has been taking the lead in looking at the feasibility of such missions

and scenarios for mission to Europa. Now, the first mission that we've been talking about, dedicated Europa mission, would be an orbiter. There is a possibility of having a small lander attached, but the key scientific questions we want to get at, the first step is to do an orbiter, sort of do for Europa what Mars Global Surveyor did for Mars. We don't have a good idea of the topography of Europa.

To confirm whether there's an ocean and really characterize the ice shell and the presumed ocean beneath, we need gravity and altimetry, measuring the distance to the surface and through measuring the gravity field, understand how Europa is warping tidally as it moves in its eccentric orbit around Jupiter. By measuring the topography and altimetry as Europa orbits, we can characterize that ice shell and the ocean. So you really have to be in orbit around Europa, which is not an easy thing to do, right?

You're in the huge gravity well of Jupiter. So it takes a lot of propellant. That takes a lot of mass. And so it's a lot of propellant, that takes a lot of mass, and so it's a difficult mission. And the mission would also complete imaging of the surface. Really, we have very small portions of the surface imaged at high enough resolution to do the kinds of science we're trying to do to understand the formation of surface features and what they tell us about the history of Europa. Also, to get at what this dark reddish ruddy stuff on the surface is. It's these spots, almost like freckles.

Right, exactly, the things that might be related to melting and or convection. We need a better spectrometer than the Galileo mission had. The Galileo mission was orbiting Jupiter, remember, making occasional flybys of Europa, whereas the Europa orbiting mission, probably called Europa Explorer, would actually orbit Europa itself for several months and be able to make detailed measurements. And not to forget the very important science goal of trying to locate liquid water, right? If you're trying to understand habitability, you want to know if it's chemical energy. You want to know if there's liquid water at Europa. But where is that water?

So we think there's a global ocean. But we also want to understand whether there's shallow melt within the ice shell, right, beneath these freckles. If there are blobs of warm ice that have come up toward the surface, they may cause some melting right within the ice shell. That could be a place where life might thrive. Barring the chance to go to Europa, at least for a few years yet, it's going to be a while, I was very surprised to learn recently that there is something of a Europan analog here on Earth in the far Arctic. Talk a little bit about that because I know you've gotten somewhat involved with

this expedition that is now underway. And what's more, you have a student, I guess, who's on it. Yeah, yeah. Davnet Gleason, she's an Irish national, contacted me several years ago, was interested in becoming a University of Colorado grad student, said she wanted to combine her geology background with planetary science and do Europa. A couple of years ago, Steve Graspy of the Canadian Geological Survey contacted me and said he had found this very interesting site in the high Arctic, 81 degrees north latitude, close to the North Pole, on Ellesmere Island.

And this place is stained by sulfur and sulfur compounds, springs of sulfur-rich material coming up through and onto glacial ice. It is literally yellow snow or ice. Right, right. I wouldn't want to get the yellow snow. Frank Zappa was there. snow or ice. Right, right. I wouldn't want to get the yellow snow. Right. Frank Zappa was there. And this stained ice is teeming with microbes as well, right? It's the kind of place we dream might exist in those ruddy spots on Europa. Could there be microbes under the surface there? microbes under the surface there. So we don't know that the chemistry is just like Europa's, but the environment of ice that's contaminated with evaporite materials and sulfur,

and where there is some melt below the surface, and we're not sure of the source at this site on Ellesmere Island, is an intriguing analog for exploring Europa. It's a miniature version, but we want to test out remote sensing techniques, the kinds of techniques we'll send to Europa. Well, here we can go on the ground. Oh, it's expensive and difficult to get up there, and the Planetary Society has helped sponsor this field expedition. So Dovnit's chief goal there is to do remote sensing. She has a handheld field spectrometer, and she'll be taking spectra from the ground

and from helicopter and comparing to satellite data obtained of the site as well. Steve Graspy is a geochemist, so he's analyzing the chemistry, and some of his preliminary work shows some very odd cold ice chemistry. In the future, we hope to return to this site with more sophisticated techniques. Someday we want to send the lander to Europa and scoop up some of that stuff

and determine if there are organics in it. Well, we'd better be able to do that here on a terrestrial site, and we know there are microbes living there, and see what's there. This conversation has gone faster than any I can remember on the show. We are essentially out of time. When do you think we might see the Europa Explorer mission or whatever name it ends up with? Well, right now, a lot of that is up to Congress and our friends there.

The mission has been proposed and recommended by National Research Council committees, by the scientific communities, and reiterated. However, with NASA's budget issues and their push toward going back to the moon, it's not a priority right now. So it's in the hands of Congress as to whether they want to be funding that mission. If that mission gets a new start soon, then we may see launch in the time window of 2015 to 2017. And so arrival

in the Jupiter system in the early 2020s. Wow. So it's a long time off. Yeah. But outer solar system missions take a while to get going off the ground. And that's why we should be starting now. It seems that water is common to many large icy satellites. Oceans inside icy satellites could be the most common habitable environments in our universe. We need to go study our solar system's best example of such an ocean. Accepting Mars, can you think of any place else in the solar system that should be more of a target for our scientific investigation? I don't think more of a target, but clearly Enceladus and Titan are key

places to go to understand water in terms of these geysers that have been discovered on Enceladus, and organics, which are common on Titan and presumably within Titan as ground organics, groundwater, ground fluids. Right now we have the Cassini spacecraft there, and we're working to develop what are the next set of questions, what mission would you send back to the Saturn system. So that's still being developed and considered, whereas Europa, we know the questions to ask. We know how to address them, and we're ready to go.

I hope we go soon. Thanks very much. Thank you. It's been a pleasure. Bob Pappalardo has been our guest. He's a principal scientist now at the Jet Propulsion Laboratory, formerly of the University of Colorado and still with ties there. And welcome once again to Southern California.

Thanks so much. We're going to welcome Emily Lakdawalla for a return visit with today's edition or this week's edition of Q&A. And right after that, it'll be Bruce Betts with What's Up. I'm Emily Lakdawalla back with Q&A. There are two reasons why it's unlikely that Iapetus's belly band of mountains could be the swept-up remnants of one of Saturn's rings. First of all, Iapetus is one of the outermost moons of Saturn, and it's well outside Saturn's Roche zone. Inside the Roche zone, Saturn's gravity is strong enough

to overcome the self-gravity of small particles in the Saturn system, so they can't form moons. They stay separate as rings. Outside the Roche zone, the particles can hang together and form moons. All of Saturn's large moons are outside the Roche zone, and even if there were a ring at Iapetus's position, it would not be aligned with Iapetus's equator, because the moon's orbit is unusually inclined to the plane of Saturn's rings. Iapetus would interact with a ring by plunging into and out of it on its inclined orbit, so ring material would land all over the moon, not just at its equator. It is theoretically possible that Iapetus was not always so far from Saturn or so inclined to its plane,

but drastically changing its orbit would require the presence of another very large moon close to Iapetus's orbit to help move it, and no such moon exists. We'll have to look for some internal origin for Iapetus's strange belly band. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Matt Kaplan is here again for another edition of What's Up here in the studio. Hi, Matt. How are you doing?

I'm great, Bruce. Good. Excellent. Something's wrong, though. I just have this sense, my spider sense is telling me, oh, yeah, I know. It's backwards day. Bruce, what's up? No, you tell me, Matt. Matt, what's up?

Well, I am because I got some sleep last night. It's been the first time in several days. But beyond that, Bob Pappalardo, you helped to get him on the show this week. So thank you for that. I know you're also involved with that expedition that's underway to Ellesmere Island that we talked to Bob about. Yes, I've loaned them half my brain to take to the Arctic. I wasn't using it anyway. No, we are pleased to be sponsoring, enabling the expedition to the Arctic,

and we will have regular coverage on planetary.org, including updates from the high Arctic. That's what's up for people on Ellesmere Island. And we're going to try and get some reports as well on the radio show. We'll see how that goes. We might have to wait until they get back, but if we're really lucky. We'll have a full report after they come back for Planetary Radio listeners about the yellow ice of Ellesmere. The yellow snow.

The yellow snow. With sulfur, sulfur, mind you. There are other things up as well. Planets, of course. I hope people have been checking out Saturn and Mars. They grew snugly, grew close together. Now, I'm afraid things aren't working out, and so they are separating in the night sky. But still kind of close together over there in the west, shortly after sunset, you can see them. So sad. You've also got Venus in the pre-dawn sky, looking like an incredibly bright star. In the land of this week in space history, we have one somber note,

which was in 1971, three cosmonauts on Soyuz 11 died upon re-entry to the Earth's atmosphere, one of the losses of the Soviet space program. And also from what was to become the Soviet Union, program and also from the uh what was to become the soviet union the tunguska explosion occurred in 1908 a planetary impact leveling forests killing creatures but fortunately in siberia so there weren't too many people hanging around but a good warning to the rest of us a very good warning let's just move on and i'll tell you more about it, shall I? Random Space Fact! The Tunguska event had an energy equivalent of 10 to 20 megatons of TNT. Yeah, good size warhead. Yes, and we actually have stacked 10 to 20 megatons of TNT right next to our building here. No, but for reference, the Hiroshima atomic bomb was 20 kilotons,

so 500 to 1,000 times smaller than the energy released by the Tunguska event. And we think this is a scale of event that happens once every few hundred years on the Earth, and so kind of a nasty awakening. Some good news. Also know that the Planetary Society and others in the world are working to try to find things like near-earth objects that might be dangerous and figure out what to do about them. Tirelessly. Tirelessly. In fact, that's why Matt hasn't slept for several days. But in our trivia contest we ask you who, who was the head of NASA? Who was the so-called NASA

administrator when Apollo 11 landed on the moon? How'd we do, Matt? Well, the answer, it turns out, is somebody who is pretty near and dear to the Planetary Society because, as one of our regulars, Torsten Zimmer, pointed out, we even named an award after him, the Thomas O. Payne Memorial Award for the Advancement of Human Exploration of Mars. That's still being awarded periodically. But our winner this week is Barbara Bethard. Barbara is from Baymanette, Alabama, and she did indeed say Dr. Thomas O'Pain, NASA administrator

at the time of Apollo 11. Yes, and he had a great deal of connection with planetary society before his untimely passing, and we still do periodically award that to those who are furthering the possibility of future human exploration of Mars, which is one of the things he really wanted to see and advocated. Barbara, we're going to send you a T-shirt. How's that? Good deal, huh? Great deal. And if you want to get that great deal, send us your answer to the following question or statement.

Name the four, all four of the so-called NASA Great Observatories, NASA's self-named Great Observatories, all four of them. Send us your answer. Find out how at planetary.org slash radio. And when do they need to get those entries in by, Matt? They've got until July 3rd, 2 p.m. Pacific time, and that will get them into the contest that we'll announce the winner of in a couple of weeks. Excellent.

Can I mention one other thing? No. We got this cute message. I'll do it anyway. All right. From one of our regulars, another regular, Dominic Turley, who was thanking us for all the Canadian content when we did the piece on the Sudbury Neutrino Observatory. He went to the University of Gulf. I hope I'm pronouncing that correctly.

He said that there was a TV screen in the lobby of the physics building hooked up to the Neutrino Observatory, so you could stand there and wait for a flash from a neutrino. Sweet. Yeah, not ready for prime time, but... Well, we'll have to check. Maybe they've got a webcam now for those truly bored. You know, I bet they do. I bet they do.

I'm going to check that out. They don't get flashes very often. Now we're done. All right. Everybody go out there, look up in the night sky, and think about the miracle of cardboard. Thank you, and good night. Cardboard. Cardboard is like, it must have made that guy think of his shield, right?

What's it called? The Whipple shield? Yeah, right. The corrugated cardboard. I'm sure that's what Fred Whipple was thinking when he thought of a shield for micrometeoroids in space. So we have cardboard to thank for that. So once again, think about the miracle of cardboard. Bruce Betts is 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. Have a great week, everyone. Thank you.