Planetary Radio: Space Exploration, Astronomy and Science - A Salty Sea on Mars

Episode Date: March 29, 2004

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A salty sea on Mars. This is Planetary Radio. Welcome everyone, I'm Matt Kaplan. We once again set sail for the Meridiani planet, where the Mars Exploration Rover Opportunity has found conclusive evidence of, my goodness, an ancient sea. Our guest played a big role in this discovery. Ken Herkenhoff is the microscopic imager lead. Bruce Betts is back from Texas with his whole family for this week's What's Up. First, though, here's Emily.

She's wondering what happens to the twilight zone when you live in a double star system. I'll be right back. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, Could a planet formed in a binary star system have around-the-clock sunlight? There are two ways to have planets in a binary star system. In the first, the pair of stars orbits close to each other.

The two stars would behave essentially like one large object as far as the pull on the planet is concerned. The planet would orbit both stars at a great distance. Such a planet would not have around-the-clock sunlight, but residents of the planet would enjoy a spectacular double sun in the daylight sky. One such planet was discovered in October of 2002 orbiting the star Gamma Cephei. The second way to have a planet in a binary star system is if the two stars are separated by a great distance

and the planet orbits one of the two stars closely. What would the sky look like in that situation? Stay tuned to Planetary Radio to find out. I have to admit I wondered why the United States Geological Survey, or USGS, would have a planetary scientist on staff exploring Mars. The answer came from Ken Herkenhoff. Ken is a Mars Exploration Rover co-investigator with special responsibility for the first instrument that let scientists get a really up-close-hand personal look at the Martian surface.

We talked just a few days after NASA's momentous announcement about the sea that once existed on the Red Planet. Ken Herkenhoff, would it be exaggerating from what we currently know to say that some many millions of years ago we could have said surf's up? Well, I don't know about surf, but certainly there was water flowing on the red planet and we don't know how deep it was or how extensive, but it looks like it might have been a very large body of water and was flowing for some time. The instrument that you have acted as the lead for on the Athena payload package,

the microscopic imager, played a big role, maybe the major role, in being able to tell us that not only was the Meridiani Planum wet, or at least this piece of the Meridiani Planum, but it was underwater. That's true. It did play a key role, and it's been very exciting. I didn't know what to expect from the microscopic imager before we got to Mars with the Mars Exploration Rovers, but because we had not seen Mars at this resolution before, we expected there would be some unexpected discoveries, and sure enough, this was one of them. Now, in talking to some of the geologists who are also on your team in past shows here,

they were also very excited to have this instrument. They really compared it to being out in the field with their little pickaxe and their little field microscope. Does that hold for you? Exactly, and in fact, that's how we designed the microscopic imager, to emulate a geologist's hand lens, which is also known as a loop, a jeweler's loop. It's about a 10-power lens. So the camera gives us that kind of a view that is very helpful in interpreting what we're seeing on Mars.

Before we get to talking about this evidence, and there is a great article about this on the Planetary Society homepage, planetary.org, let's talk about your background a little bit. You came out of Caltech. You spent time at JPL. You're now with the U.S. Geological Survey on the Astrogeology team in Flagstaff. How is it that the USGS made the transition, the evolution, from putting those neat little markers on top of mountains to helping to explore Mars?

Well, many years ago in the early 60s, Gene Shoemaker, one of the first planetary geologists, put together a group of people and formed a new branch, astrogeology branch, of the U.S. Geological Survey, initially in Menlo Park, and because he loved Flagstaff, moved everybody to Flagstaff soon thereafter. All these southwestern geologists. Right. Well, at that time, the main interest was in the geology of the moon,

which they were doing by observing the moon through telescopes, and Flagstaff was a great place to do that, and they had a telescope there that they used to do the lunar geologic mapping in the 60s. So that division is still what you are part of today? That's right. Yeah, Gene started up and kept it going for a long time. He died in a car accident in Australia in 97, but we've been carrying on in his footsteps. Tragic loss.

Indeed. And someone who is mentioned frequently on this program, and of course, is the namesake of our Shoemaker NEO Discovery Program, the grant program that the Planetary Society offers. I count myself as lucky to have met him and to spend some time in the field even with him. He was my mentor, and I really miss him. Now still, if I were a member of Congress saying to the USGS, what is in it for this country to be having geologists and planetary scientists study another planet? What can we learn that's going to help us here?

Well, what I'm particularly interested in is comparing climate changes that we've seen on Mars with climate changes on Earth. And as you know, climate change on Earth is a big issue these days, both for scientists and policymakers. Earth is a big issue these days, both for scientists and policymakers. Mars is somewhat simpler than the Earth in that currently, anyway, there is no extant ocean. We don't know that there's any life on the surface, both of which complicate the climate on Earth significantly. So we're thinking that the external climate forcing, the changes in solar luminosity, the changes in the obliquity, that is the tilt of the rotation axis of the planet relative to its orbit, could be seen more clearly on Mars than it is seen on the Earth.

So a lot is really the answer. Well, yeah, in a couple words, that's right. You spent most of the 90s at JPL. We are talking to you back there at the moment because you're part of the science team for the Mars Exploration Rovers. That's right. What was the nature of the work that you were doing at JPL? The same kind of work. I've been working on Mars ever since I started on my thesis.

My advisor, Bruce Murray at Caltech, and at the time Larry Soderblom, who was a Fairchild scholar, got me started on the polar regions of Mars, the geology of the polar regions. And I continued that work and was doing that at JPL, and at JPL was lucky to get involved in the Mars Pathfinder mission, and that experience is what directly led to my involvement in MER. So how did you get pulled into MER? Was that Steve Squires doing? Steve Squires asked me to join the team, and of course I was happy to join. Now what does it mean that you were the lead for the microscopic imager? Were you involved with the physical development

of the instrument? Yeah, that's right. And Jim Bell, who's the payload element lead for the PanCam, and I worked together on the camera design. The cameras all share common electronics, work together on the camera design. The cameras all share common electronics, so what's different is the optics on each camera. And so I spent a fair amount of time on the optical design and trying to optimize it for various things, limit the aliasing, that kind of thing. And then, of course, we were heavily involved in calibration of the cameras here at JPL in 2002. Jim Bell was our guest just a couple of weeks ago on the show.

We talked about the PanCam, of course. Was it a challenge to take this very high-resolution camera, particularly compared to what's been on the Martian surface before, and get it to work not only looking off toward the horizon but also very close up through your instrument? The optical design was helped along significantly by a number of people here at JPL and a contractor, Greg Smith, in Pasadena. They did a great job designing the optics.

We told them what we were after, and they put it together. And obviously, as you've seen the pictures, they did a great job. So for me personally, it was not a challenge because we were assisted by such capable people. It really seems that this spectrum of instruments that Steve Squires brought together has done an amazing job. I wonder if anybody realized how well all of these would work together, and I'm sure no one realized what incredible data they would return. Well, we did select a payload with synergy in mind, and it has really paid off. It's a credit to Steve and the entire team to foresee that these instruments would give us complementary information and that the synthesis of the various data sets would be so powerful, and it's great to see it working so well.

We're talking with Ken Herkenhoff. He is our guest this week on Planetary Radio. Ken, I teased people saying we would get to that evidence for standing or moving water over the surface of Mars, but I think now we're going to have to do it after a break. Can you stay with us for a minute? You bet. We'll be right back after this message with more from Ken Herkenhoff, and we will talk about that salty sea on Mars.

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Planetary Radio returns with our guest this week, Ken Herkenhoff, geologist, planetary scientist for the U.S. Geological Survey, a member of the astrogeology team, and a member of the science team for the Mars Exploration Rovers. He is the lead for the Microscopic Imager, which is an instrument that sure paid off, well, has paid off many times over, over the last few months of the two rover missions, but especially with this amazing announcement last week. A lot of you guys, enough of you, are now convinced that there was once water on the surface of Mars, not just soaked into the sand up there, but actually at least a pool and maybe a lot more.

That's right, and it has been very exciting lately, an opportunity to see these data come down. What we found is that there are evidence of what geologists call crossbeds or cross laminations. And specifically, the types of crossbedding structure that we see is diagnostic of fluid flow. While many of us were fairly convinced of that earlier on, NASA rightly sent out some of the data for review, outside review, and it was good to hear that our terrestrial colleagues agreed with us mostly, that the features we're seeing are diagnostic of fluid flow. So not only was water standing on the surface of Mars, but it was flowing enough to cause these crossbeds.

And these crossbeds really are only seen on Earth, have only been formed, so far as we know, by water. The specific type we're seeing, they're smaller. You can also get crossbeds from wind-driven sand. Sand dunes will form crossbeds from wind-driven sand. Sand dunes will form crossbeds, but they're larger and their structure is different in detail than what we're seeing here. So that's how we sorted that out. Now, this being radio, we should refer people to some of the actual images, which are, of course, on the JPL Mars Exploration Rover site and also in that article on the Planetary.org,

Mars Exploration Rover site, and also in that article on the planetary.org, the Planetary Society website, because we're talking about this little piece of an image taken by the microscopic imager. It's just maybe, what, three or four centimeters across, one of them? And you guys have kindly drawn in some lines to take us laypeople and make it easier for us to see some of this cross-vetting? That's right, yes. And what you said is true. Each MI image is about three centimeters, a little over an inch across, so that gives a feeling for the

scale here. So these are little tiny ripples at the bottom of an ancient sea on Mars and you can see how some of the layers are cut off or truncated by other layers, and that's the kind of diagnostic structure that we needed to interpret this story. Now, while the microscopic imager provided much of this evidence, I don't believe it was the only evidence. That's correct. In fact, it's the synthesis of all the data sets that really nailed this down.

The PanCam, of course, was used to recognize what looked like crossbeds from afar and allowed us to go in and pick spots where we did even mosaics of MI data, and you'll see those on the website as well. But more importantly, the chemical information that we get out of the mini-tests, mini-thermal emission spectrometer, remotely, and the in-situ spectrometers, alpha particle X-ray spectrometer and the Mossbauer spectrometer, all indicated that there were sulfate minerals in such abundance that we had to have an evaporite sequence here. There was just too much sulfate to explain any other way.

Does this also help our understanding of the famous, possibly even infamous in the popular media, the blueberries? They maybe were formed by water rather than some kind of volcanic or meteor action? Now, the blueberries are interesting. When I first saw them as soon as we got off the rover down in the bottom of the crater, these spherical objects to me looked like they were just glass beads, either as you said, either volcanically or impact generated. But when we got up to the outcrop and started looking at it, particularly with PanCam and MI,

we could tell that the distribution of those spherules in the outcrop is more or less random. In fact, if it's non-random in any places, it looks like they tend to form along vertical fractures, not horizontal beds. If they were formed in a volcanic or impact event, you'd expect them to be concentrated stratigraphically, meaning that you'd see more of them at certain levels in the outcrop than others. But that is not what we see. That supports the hypothesis that they were formed in place after the rock was already formed, laid down.

Water percolating through it appears to have formed these concretions of hematite much later. Seems like the concretions in that they built up almost like pearls. Right. And the only problem that I've seen with that in the MI images is after we ground one of the outcrop or a couple of places with the rat, we see these spherules in cross-section. And concretions, you would expect to see some kind of internal structure, concentric structure, something like that. And, in fact, we don't resolve anything with EMI.

Now, that just may mean that the layering, the laminations, are finer than the 30 micron per pixel resolution that we have in the camera, and that wouldn't be too surprising. You know, they do look rather uniform inside. I bet you'd love to get some of those back here on the surface. Oh, you bet. Put them under an electron microscope. You bet.

We're talking with Ken Herkenhoff, planetary scientist, geologist, lead with the microscopic imagers on both of the Mars exploration rovers. So we can now state with great confidence that there was standing or flowing water over the surface of Mars, at least at this one spot. What are the chances that we've just hit the one tiny square of Mars out of millions or billions that had this puddle of water? Well, that's a very interesting question. And one of the reasons we went to the Meridiani site in the first place is that hematite was recognized from orbit by the test instrument on Mars Global Surveyor. And so it is a unique place in that respect that it exposes the hematite on the surface.

The regional geology indicates that this area has been exhumed. That is, it was buried by more rock material, which has been eroded away, exposing the surface that we're seeing now. So it could be that there's a lot of this stuff that is still buried or that has already been eroded away, and we're on a place that is luckily still preserved. So as you said, there could be a lot more evidence for water on Mars, more widespread oceans on Mars even, that we just don't know about. With just a couple of minutes left, what are our chances, with Opportunity still working very well up there on the Meridiani Planum,

of discovering how broad, how deep, and maybe how old this sea was? Well, what we're planning to do is, now that we're out of the Eagle Crater that we luckily landed in and have done a good job of looking at the outcrops there. Although, you know, the engineers tell me that they meant to land there. Well, it was a great shot. You know, it's been compared to a hole-in-one, and I play some golf, so I can appreciate how good a shot it was. Sorry for the interruption, but you say we've now climbed out.

Yeah, right. We're out, and we can see Endurance Crater off to the east about 800 meters away, and we're going to start driving over there as fast as we can, well, taking some data along the way and trying to understand the planes and some features that we see from orbit in the planes. But once we get to Endurance and look in, we're hoping that we'll see much more of the stratigraphic section, that is, many more layers of the rocks that are exposed in Eagle Crater in the larger Endurance Crater. Once we get there, we'll decide whether it's safe and whether we want to go down into the crater

and examine those in more detail. But even remotely, we're hoping that we'll be able to get a better feeling for how long this sea or lake persisted and how much of this evaporite, how many evaporite minerals were laid down. We can see from orbit that there are light-colored rocks exposed in Endurance Crater, but we need to get over there to see them. Well, we wish opportunity luck, and we'll note that you are on Meridiani time, one of many folks up at JPL still running on Mars time. That's right.

Your colleagues who are on Gusev time, we don't want to give short shrift to Spirit on the other side of Mars. Any news from there? And it does seem like it's been, if you'll pardon the expression, left in the dust by at least this discovery in the Meridiani Planum. Well, we did get lucky at Meridiani. There's no doubt about it. And the Gusev site is more like what we were expecting to see on Mars. And while it has been a little more disappointing scientifically,

there have been some interesting results. We've found mostly basaltic rocks, but the insides of the rocks that we've abraded with the rat show that there has been probably at least some water percolating through those rocks. And right now we're up against a large rock, about a two-meter rock, that is covered with white debris, well, or coating that appears to at least partly been influenced by water there. So they're digging into that right now. And to be honest, it's difficult for me to keep track of what's going on at both rovers at the same time.

But they're getting some good results and trying to understand how that coding was formed. And who knows what surprises may still be in store from these rovers that are still doing very well up there on Mars. That's right. We're out of time, Ken. I hope we can have you back when more of those discoveries, more of that data returns, and talk about the additional work being done between now and the end of the lives of these rovers a long, long time from

now. Already, I guess, Spirit is about to outlive its warranty. Right. Yeah, well, it's almost the end of the nominal mission on Spirit, and it looks like she's still going strong, and no signs of giving up yet. So, yeah, these could be very long missions. Well, let's hope so. Thanks again very much for joining us on Planetary Radio,

and we really will look forward to having you back. All right. It's been my pleasure. Thank you, Matt. Ken Hergenhoff is a geologist and planetary scientist with the U.S. Geological Survey, part of their astrogeology team, and a very active member of the science team for the Mars Exploration Rovers, the lead for the microscopic imager. We'll be back with Bruce Betts right after this from Emily. I'm Emily Lakdawalla, back with Q&A.

Could a planet formed in a binary star system have around-the-clock sunlight? Imagine that the planet is an Earth-like one, orbiting close to one of the stars in the binary pair. The other star in the pair would be orbiting far away, as far away as Pluto is from Earth. Our Earth-like planet might orbit its sun star very quickly, but the other star in the binary pair would move much more slowly. So for a part of our hypothetical planet's year, it would pass in between the two stars. At these times, from the surface of the planet, one or the other of the two stars would be up in the sky virtually all the time,

and there could be around-the-clock sunlight. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Back from Houston with his boys on his knee and his wife at his side, Bruce is with us for What's Up. He is the director of projects for the Planetary Society. Bruce, what's up?

Well, it's great to be here, Matt. And up in the night sky, what is up in the night sky, Daniel? A line of planets. That's right, a line of planets. We went out and looked at them just a few nights ago. Line of planets, don't miss them. Great stuff. You can see all the planets that are naked-eye right now.

Start with Venus, really easy to see, really bright thing off in the west after sunset. Then look below it to the right if you've got a clear view to the horizon, and you can see Mercury. If you look above to the left of bright Venus, you will see Mars. Keep going up in a line, as Daniel points out,

and you will see Saturn high in the sky and farther over, starting to be towards the east, Jupiter also extremely bright. Even though I can't, even though the only one I can really understand is the moon. But I bet you understand the others. I was looking at them last night. I was in line for a movie, and there they were. It was just spectacular, just as you've described. It's true, and the moon's going to go visit with Jupiter next, I believe, shortly.

Yeah, Jupiter. I'm going with Jupiter. I could see it headed that way. What else do you have for us? Okay, this week in space history. No, it's daylight right now, Daniel. You can't see it right now. Okay.

This week in space history, on March 29, 1974, Mariner 10 flew by Mercury for the first time, the first and only spacecraft to have ever flown by Mercury to date. Moving on to random space fact! Most radio dishes

are paraboloids. They have parabola cross sections because parallel rays coming in, radio waves, it could be radio, light, whatever, they all get focused to one point, which is typically where they put the receiver. Not all of them are that way, and they do fancy things otherwise,

but most radio dishes, paraboloids. It's all photons to me. Paraboloids. Last week's trivia question, we asked you, what is the shape of the trajectory of an object that just has enough energy to escape the gravity of its parent body? Daniel, maybe you can give us the answer. What's the answer to that?

The parabola. Yes! Exactly. If you had a little more energy than that, then your spacecraft or whatever, an asteroid comet, would be a hyperbola. But if you have just enough energy, it's a parabola. Hey, that's the same thing that makes up those radio dishes. Isn't mathematics cool?

Matt, how did we do with the winners? We did well. We had a lot of people with the correct answer. And here is somebody that I don't think we've heard from before. Paul Grimm from Athens, Ohio, said, yes, the right shape that's just enough to get you away from here or anyplace else is a parabolic shape. And so, Paul, he just said that he's ready for his T-shirt. He just said, make it big. So I guess we'll send him an extra large Planetary Radio T-shirt.

We have to mention these folks, Karen and Ben Howard. They have entered before from Australia. And here's their answer. they have entered before from Australia. And here's their answer. And, of course, this is their response for the shape of a path followed by an object that has just enough velocity to escape the gravity of its parent body. They said a lot of young couples think the answer is eloping. Eloping.

Eloping. They'll explain it to you later. So how about next week? Okay, next week. Here's your question. What moon of the solar system looks most like the Death Star from Star Wars? Oh, and I know why. And, well, I can't even say that.

But, well, there's something about the features of this moon that makes it look like the Death Star. And it really does. I mean, that's what I said when I saw it. So, how do they enter? Go to planetary.org slash radio. Follow the instructions to enter our glorious contest. Win a Planetary Radio t-shirt. Matt, did you have anything you'd like to add?

Tell us. I was going to ask you if you had any announcements. I do have one. Please go ahead. Congratulations. I want to congratulate NASA on the successful flight of the X-43 on the second try. This scramjet, little remote-operated vehicle that flew above Mach 7, about, what, 5,000? That was it right there.

It was flying by. It just signaled to us. It came by here. It was very fast, so we didn't get to hear it for long. But going more than Mach 7 or about 5,000 miles per hour, which is just a wonderful demonstration of new technology and holds out the promise that someday I'll make the commute from Long Beach to Pasadena, California in three seconds. Cool!

It's the stopping that's hard. Yeah. Did you have anything else for us? He's at a loss. Okay. How about you, Daniel? Anything you want to add? Anything you want to mime? That's mom. Mom's a good mime. Oh, she's in the box. Okay. Oh, she can't get out. She's in the glass.

She's in a parabola. Oh, she's in a parabola. My God, a fresh mime routine. Parabola, parabola, parabola. It's lost all meaning for me now. There's a mime stuck in a parabolic box. That would be an interesting thing to see anyway, wouldn't it? We better get out of here.

Okay, everyone. Say goodnight, Bruce. Look up in the night sky. Think about... A line of planets. A line Think about... A line of planets. A line of planets. A line of planets. What better than that?

Thank you, and goodnight. That's Bruce Betts, the Director of Projects for the Planetary Society, and the whole family is here for What's Up. So, there was a sea on Mars. Did any living things call it home? We'll talk about this possibility with astrobiologist Andy Knoll on next week's Planetary Radio. I hope you'll join us. Thanks for listening.