Planetary Radio: Space Exploration, Astronomy and Science - Mars Express Confirms Lots of Polar Ice! Where's the Rest?

Episode Date: March 26, 2007

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11 meters of water covering Mars? That's nice, but how about a kilometer? 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. I said you wouldn't have to wait long to hear a conversation about the recent announcement of huge amounts of nearly pure water ice at the Martian South Pole.

Well, here's your opportunity. Jeffrey Plout is a JPL geologist and co-principal investigator for the Mars radar instrument on the Mars Express orbiter. He'll tell us why finding all that frozen water wasn't really a surprise.

The big question is, where's the other 99 percent? Later, we'll hear about something in the sky that Bruce Betts is genuinely afraid of, even as he tells us what to look for at night. And we've got another Planetary Radio t-shirt for a space trivia contest entrant. Emily Lakdawalla's latest Q&A is just around the corner. Here's a big story I picked up from Emily. It seems that Saturn's little moon Enceladus, however improbable it may sound, has a lot in common with bodies like Europa. Two just-announced studies have found, one, evidence of a liquid water sea under the Enceladus South Pole, and two, the water plumes shooting up out of the 500-kilometer ball

contain hydrocarbons and other reactive chemicals. Unfortunately, the Cassini orbiter isn't capable of detecting more complex molecules such as amino acids, but they could be there. So should we be looking for life on Enceladus? Future mission planners, consider yourselves on notice. You can learn more at planetary.org. Elon Musk says, of course he'll try again. His SpaceX Falcon 1 enjoyed a successful liftoff during a second attempt, but something went wrong when the rocket was about 161 kilometers or 100 miles up. Rocket science is hard, isn't it?

Here's Emily on a literal race to the stars. I'll be right back with Jeff Plout. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, I've heard that New Horizons was the fastest spacecraft ever launched. So when will it overtake the Voyagers to become the most distant spacecraft from Earth? New Horizons will never overtake either Voyager spacecraft. It is one of only five spacecraft that are escaping the solar system.

The others include Voyager 1 and 2 and Pioneer 10 and 11. The Pioneers were launched first and were, for a while, the most distant spacecraft from Earth. But the Voyagers attained higher speed, so in 1998 Voyager 1 passed Pioneer 10 to become the most distant spacecraft. Voyager 1 is currently more than 100 astronomical units from Earth and is escaping the solar system at about 3.6 astronomical units per year. New Horizons is actually moving faster than that, about 4.6 astronomical units per year. So why won't New Horizons ever catch Voyager 1? Stay tuned to Planetary Radio to find out. Planetary Radio to find out.

The European Space Agency's Mars Express orbiter got big headlines a few days ago when it was announced that the craft's Mars' radar had found a huge amount of water ice at the red planet's south pole, enough to form a 36-foot layer around the entire planet. Jeff Plout and others weren't surprised. Jeff is principal scientist in the geophysics and planetary geosciences group at the Jet Propulsion Lab, but he's also a co-principal investigator on Mars's the Mars Advanced Radar for Subsurface and Ionosphericospheric sounding. The first thing I asked him when we sat down in the JPL Visitor Center is just how far down his radar can reach beneath the ice. Two and a half miles, over three and a half kilometers are the figures for where this deposit of ice is thickest in the south polar region of Mars. I should say off the bat that although 36 feet or 11 meters or so of ice

spread around the entire planet sounds like a lot, it is a lot, but it's not a shock as far as what we knew about this material before Mars has ever arrived at the planet. What we were able to do that was new was we were able to measure the base of this ice deposit where it's in contact with the underlying material and make a much more detailed map of the thickness of the ice in the south polar region. And so the number that we then come up with is a much more accurate estimate than what had been achieved before just using the topographic information. You say it wasn't a surprise, but aren't we still looking back to not all that many years ago

when, yes, we thought there was some water on Mars, frozen or otherwise, but we really were still, after all, we were trying to follow the water. One of the revolutionary moments in our exploration of Mars actually came with the accomplishments of the Mars Global Surveyor spacecraft, which in the late 90s began surveys of Mars using a different kind of set of instruments than what we had done in the past in the 70s. And in particular, the laser altimeter, nicknamed MOLA, obtained a topographic map of the entire planet

at much higher resolution than any other data set that we had had in the past. And it was on the basis of those data, the topography data of the polar regions of Mars, that the first estimates were made of just how much water ice was actually locked up at the poles. It was very much in line with the numbers that we've come up with based on our subsurface sounding. So again, that's why I say it wasn't a real shock, but we're now able to not only measure the amount, but also how it's distributed in different areas around

the polar regions. And also, since our radar waves penetrate through the material in a certain way, it tells us something about that ice itself. And I was just going to get to that, because I've read that the data indicates that this is, in large part, pure water. Well, that's right. As the climate of Mars went through changes, cycles of climate change, more or less dust was deposited at the poles along with the ice. Now what we found with the Marsis radar is that as our radar waves penetrate through the material, reflect off of the boundary of the ice with the surrounding crustal rock, we get a very strong reflection and very small amounts of loss of the signal during that round trip. Now, that is consistent with very clean ice.

That's why we're able to say something about just how pure this ice is. It's based on the attenuation or the lack of attenuation of the signal. This is pretty significant because it tells us something about how the climate might have been changing when the dust was deposited, but it also tells us that this pile of material is over 90% water ice, and that gives us a better handle on the inventory of water on the planet. Do we have now, through MARSIS, anything like the data that would tell us how old this ice is, the lowest layers of it, much as we've been able to do

through coring through the polar ice here on Earth? Well, the information on the age of the material, the best information comes from impact crater abundances, which is the way that we acquire it. Just like the rest of the surface. Right. The way we learn at least relative ages from place to place on the surface of Mars is by counting the number of impact craters.

We assume a particular rate of impact bombardment, and this allows us to estimate roughly the age of a surface or how long a surface has been exposed to the flux of impactors. Now, one of the interesting differences between the North Pole and the South Pole layer deposits is that the South Polar deposits appear to be much older than the North Pole. At least the surface that's exposed today in the South has many dozens of small impact craters, whereas in the north there are hardly any, maybe a handful, a small handful, and they're very small. This leads us to conclude that that surface in the south polar region has been exposed but stable for probably tens of millions of years,

exposed but stable for probably tens of millions of years, whereas in the north, the upper surface seems to be actively recycling and either erasing craters by erosion or by continued accumulation of material. So the age of the south polar ice, it's not known precisely, but we can at least infer that it's rather old, depending on how you look at it. Geologically, it's tens of millions or more years old. Of course, in the geologic history of Mars, that actually may be considered young because most of the resurfacing activity that we have evidence for on Mars is billions of years old. So these deposits are still in the most recent epoch of Mars history, but they don't seem to be related to the

current climate cycles because, as I said, the upper surface appears stable and appears to be, to have been collecting impacts for many tens of millions of years. What else does this tell us about the planet and other parts of the planet as you move away from the poles toward the equator? Well, we are still looking for the rest of the water. The reason I put it that way is that based on evidence from other parts of the planet, it's clear that huge volumes of water float across the surface of Mars, and that water did a lot of work on Mars in the form of erosion.

There are gigantic channels, what we call the catastrophic outflows. There's a whole system associated with Valles Marineris, the Grand Canyon of Mars. And based on the amount of material that's been removed, you can get a pretty good estimate of just how much water was involved in doing that work. And it turns out that the numbers that you come up with are in terms of a global layer, which we said for the polar ice is about 11 meters from the south and probably an equivalent amount in the north, so maybe 20 or so meters of a global layer is locked up currently at the poles,

the amount that's needed to do all that erosional work is measured in hundreds of meters, maybe even a kilometer global layer. That water is not, all of those hundreds of meters are not locked up at the poles. All we see is a few tens of meters locked up at the poles. So there's still a huge inventory of water that we have yet to identify the fate of. Now some of it may have escaped to space through processes at the top of the atmosphere. There may have been what's called impact erosion, where large impacts actually can rip away a significant

amount of the atmosphere. The solar wind, of course, can do work on the atmosphere and remove some of it. But it's also likely that a significant amount of this water that was released from the subsurface in catastrophic flow events probably percolated back down into the subsurface, and that's where it remains today, either in the form of ice or perhaps deeper where things are a little bit warmer in the form of liquid water. How will we find that water? I'll ask JPL's Jeff Plout when we return in a minute.

This is Planetary Radio. I'm Robert Picardo. I traveled across the galaxy as the doctor in Star Trek Voyager. Robert Picardo. I traveled across the galaxy as the doctor in Star Trek Voyager. Then I joined the Planetary Society to become part of the real adventure of space exploration. The Society fights for missions that unveil the secrets of the solar system. It searches for other intelligences in the universe, and it built the first solar sail. It also shares the wonder through this radio show, its website, and other exciting projects that reach around the globe.

I'm proud to be part of this greatest of all voyages, and I hope you'll consider joining us. You can learn more about the Planetary Society at our website, planetary.org slash radio, or by calling 1-800-9-WORLDS. Planetary Radio listeners who aren't yet members can join and receive a Planetary Radio t-shirt. Our nearly 100,000 members receive the internationally acclaimed Planetary Report magazine. That's planetary.org slash radio. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. My guest is JPL planetary geologist Jeff Plout, who is also co-principal investigator for the Marsis radar instrument on the Mars

Express orbiter. Jeff was telling us where we might have to look to find the vast amount of missing water on the red planet. Will Marsis or other types of instruments, other radar instruments perhaps, be able to help us in looking for this other water, perhaps, be able to help us in looking for this other

water, which may be below the surface and certainly is not something that the rovers have been able to dig up with their wheels? Well, this is really the motivation for instruments like MARSIS and also the companion instrument called SHARAD, which is flying on the Mars Reconnaissance Orbiter spacecraft that's recently begun its work. In theory, if there were liquid water within the first few kilometers of the surface, we should be able to detect it with these instruments. This is what our models tell us. But at the moment, and we've been working for about a year and a half now with Marsis on Mars Express,

we don't have any kind of smoking gun obvious signature of shallow liquid water, even in the warm equatorial regions. Now, there may be reasons that it may actually be there, and out of bad luck we may not be able to detect it. There may be particular characteristics of the rock that it's contained in. But really our suspicion is that although there's a lot of water ice near the surface, the liquid ice is rather deep. The liquid water is rather deep,

and perhaps it's out of reach of the detection capability of even Mars, which is designed to look as deep as was feasible considering the spacecraft that we were on. You know, the absence of liquid water in these data sets, at least so far, is not completely consistent with some other observations that have come, for example, from the Mars Orbiter Camera on Mars Global Surveyor, which in a recent announcement detected changes in these gully flow features on the walls of impact craters. It was suggested that those changes may have been caused by transient flows of liquid water. There's controversy about that interpretation. There's also a question, if we assume it was liquid water,

well, where did that water come from? Was it the result of melting of snow or surface ice? Was it released from the subsurface? And if it were released from the subsurface, that means that in the shallow regions of the Mars crust, there are, at least from place to place, from time to time, areas that are warm enough, conditions are right, for liquid water to exist. We're targeting these areas that have been identified in the image data, suggesting that there's liquid water.

Haven't seen it yet, but we're still looking. This leads me to think, once again, that what we don't know about Mars is still far greater than what we do. Yeah, and that's what makes this an interesting business, is that it seems that every time we learn something new, instead of reducing the number of questions, it actually raises two or three more. That's science for you. Yeah, so the questions keep on multiplying. We get answers to some of these things.

We get a little closer to understanding the reality of Mars. It's the business of geology, which is essentially a mystery, and we are the detectives in this mystery trying to take a look at all the clues that we can assemble and piece together a story. And on Mars, you know, we've been lucky enough that we have some of these little robot geologists on the surface, but the vast majority of our information from Mars comes from what we call remote sensing, from satellite observations. And it's pretty far removed from what geologists do on the Earth, where they go out to the field site, they collect, as you mentioned, they collect ice cores from ice sheets and are able to analyze their samples back in the laboratory.

We don't have any of those tools at our disposal from Mars. So it's a real challenge, and what we find ourselves doing is we kind of use the word constrain. We try to kind of narrow the problem down smaller and smaller until there are only a few possible explanations left. You're also project scientist for Mars Odyssey. Yes, and that's what we call wearing several hats. It's kind of the coordinating scientist on the Mars Odyssey mission. And Mars Odyssey, of course, was launched in 2001, 2001 Mars Odyssey.

Hence the name. And now, six years later, still chugging away, getting very, very valuable, spectacular scientific results with its camera system, thermal infrared camera system, the gamma ray and neutron detectors, which were key to understanding the ground ice of the Arctic regions of Mars, which is a different topic but related to the layered ice deposits. And right now, Odyssey is in what we call the extended mission. We accomplished all of our primary mission objectives over about two or three years of operations, and now we are continuing to collect data, and one of our major roles, in addition to

doing science, is to provide a relay for communications that are coming from the rover, Spirit and Opportunity. And Odyssey is the prime relay for those, and we'll actually be serving the same function for Phoenix once it arrives in, what, a year and a half or so. Yeah. And even down the road, we're looking towards trying to still be around to do that job when the Mars Science Laboratory's MSL rovers arrive in the next decade. And I suppose you never know when another member of the team of robotic emissaries

that we have at Mars might be able to back each other up in research that we may not even have an inkling of yet. Well, that's right, and that's what's so vital to the way that we're conducting, we're able to conduct this Mars exploration program now, is that we can feed results from one experiment on one spacecraft or lander into the observations that another is making. And sometimes this kind of synergy can just kind of go back and forth and actually lead to the kind of thing where the sum is more than all of the parts. We call it discovery-driven science.

There are other kind of buzzwords or names that are used for it. But, for example, the Odyssey finding of ground ice led directly to the choice of the Phoenix landed mission and its landing site to go to these Arctic regions where Odyssey has demonstrated there's water ice in the very near subsurface, and just with a few scoops of its shovel, Phoenix should be able to pick up this material and analyze it in its mobile laboratory. Jeff, we're out of time. Thanks again for joining us on Planetary Radio, and we look forward to further results from Marsis and Mars Express, as well as Odyssey, and getting down to that polar region

with the Phoenix lander in about a year and a half. All right. Thank you. It's been a lot of fun. Jeff Ploud is Principal Scientist, Geophysics and Planetary Geosciences Group at the Jet Propulsion Laboratory, Project Scientist for 2001 Mars Odyssey, but as you just heard, also Co-Principal Investigator for the Mars' radar instrument, radar sounder, that currently continues to sound and circle the red planet. We'll be right back with this week's edition of What's Up. I'm Emily Lakdawalla, back with Q&A.

Although New Horizons is currently moving faster relative to the sun than Voyager 1, the Pluto spacecraft will never catch up to the Voyagers. New Horizons is on a trajectory that will allow it to escape the sun's gravity, but it still feels a strong backward tug from the sun, so it's slowing down over time. Voyager 1 is also slowing down, but because it's much farther from the sun, it is losing speed much more slowly. Both New Horizons and the Voyagers had the benefit of Jupiter gravity assist to increase their heliocentric speed, but the Voyagers also got to buzz by Saturn for a second assist, an advantage that New Horizons doesn't have. So although New Horizons was the fastest spacecraft

launch from the surface of the Earth, and the first one ever to be launched directly from Earth's surface into a solar escape trajectory, it will never catch the Voyagers. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Radio. It's time for What's Up on Planetary Radio. Bruce Betts, the Director of Projects for the Planetary Society, joins us once again to tell us about the night sky and other fun stuff. Hey, welcome back.

Hey, thank you. What's going on? Well, by the way, people loved it that we were visiting at your place, your home last time, and really wondered about those stinky shoes. Yeah, I hear some people are still thinking about them. Yeah, I guess so. I don't want to think about stinky shoes very much, but it was fun. Yes, indeed.

You know what else is fun? No. Looking up in the night sky. Oh, I knew that. And if you look in the early evening, you can't miss Venus looking bright, gorgeous, brilliant over there in the west. Brightest star-like

object out there. You know, brightest object up there in the night sky, except for the moon. And we've also got Saturn up there in the evening, and it's going to be high, pretty high overhead in the early evening. It's in Leo, so go check out the Leo constellation with its brightest star being Regulus.

Pull out your star chart if you're not familiar with Leo. It's one of the few that you can almost connect the dots and pretend it is a lion. We've also got Jupiter rising in the middle of the night, looking very, very bright, and up very high in the sky in the pre-dawn as the brightest star-like object up then, and Mars low in the southeast during dawn. We also have a This Week in Space history. In 1974, Mariner 10 made its first flyby of Mercury, giving us our first view of that planet, and Messenger will be flying by for the first time next year,

and we'll finally get to see the other side of Mercury. You say first view of Mercury from up close, but really the only one, right, so far? Yes, although Mariner 10 had three flybys, so it was the first of three. But yes, all on the same side, though. So Messenger will show us the other side, which I'm sure will be a completely different color other than gray. It's covered with big signs. Exactly.

Go home. Let's move on to Radio Sportsbook. According to at least one recent study, about one Martian meteorite hits the Earth every month. That's a lot of Mars. It's a whole lot of Mars. And these are estimations for current Mars. We would have had even more Mars when the impact rate was a lot higher early in the history of the solar system.

Now, of those, a bazillion meteorites, approximately 30 have been found and identified as from Mars. Somebody ought to figure out how many Earth meteorites hit Mars on a monthly basis or whatever. They should indeed, and maybe they have, but that wasn't this week's random space fact. No. We do have a trivia contest, though. Yes, we do have a trivia contest.

We asked you, scientists from what country have provided magnets for nearly all of the recent and future Mars missions, including the Mars Exploration Rovers and the Phoenix mission? How did we do, Matt? Well, out of what I think it's fair to call a plethora of answers, we only had one that was incorrect, and I think it was because of perhaps a little bit of nationalism, but one of our German listeners.

But you hear that helicopter? Yeah. They can't see us, can they? No German listeners. But you hear that helicopter? Yeah. They can't see us, can they? No, they can't. You're safe in here. All right. It seems to be circling. Yeah, yeah.

Okay. Can we finish this up soon? Yeah, you got to go? Yeah, I forgot something. Okay. The correct answer, I assume, that you can confirm this, is Denmark. It is indeed Denmark. What an interesting choice.

We got that from a lot of people. One of them, not our winner, I'm sorry to say, Kevin Hecht, he said that they do, in fact, those little magnets come from Denmark, a friendly little earth country that is also famous for Danish, much better to eat than magnets. Well, obviously, he's never tried the magnets. I guess. They're tasty.

We had some in our DVD hardware that we sent on the MER Rovers with four million names and also had some Danish magnets in there. And, you know, if they're good on a wristband, if they make you healthy on a wristband, think what they do in your digestive tract. Okay, let's're good on a wristband, if they make you healthy on a wristband, think what they do in your digestive tract. Okay, let's not think about that. Okay, too late. Ted Seaman. Ted Seaman of Carroll Stream, Illinois. Got it

right. He said Denmark. And I want to point out that Ted Seaman also has the Space Elevator blog, which I've checked out. It's a really interesting blog. He kind of stays on top of everything that's happening with this future technology, and it's spaceelevatorblog.com if anybody wants to check it out. But guess what, Ted?

You're elevated to Planetary Society T-shirt owner status. How's that? Congratulations. And if others of you would like to be elevated to that lofty status as well, answer the following question. What planet has the smallest axial tilt? So Earth, about 23.5 degrees, axis tilting off of how it orbits around the sun. What has the smallest axial tilt? What planet in our solar system?

Go to planetary.org slash radio to find out how to enter and win your own fabulous planetary radio T-shirt. And this won't be that much of a hint, but one of them, I mean, we'll eliminate one. One of them is like 90 degrees, right, or close to it? Yeah, it's not that one. Okay. Regardless, if you can tell us which one does have the smallest axial tilt, you'll need to tell us by 2 p.m. Pacific time on Monday, April 2, April 2nd at 2 p.m. Pacific time. And that's it. We're done. All right, everybody, go out there, look up at the night sky, and think about really dark areas.

Thank you. Good night. Well, who knows what evil lurks in the hearts of men? The shadow knows, and so does Bruce Betts, the director of projects for the Planetary Society, who will join us once again next week for another edition of What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week, everyone. Thank you.