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NASA Images Provide Possible Evidence of Water on Mars

December 7, 2006 at 6:45 PM EDT

JEFFREY BROWN: The tantalizing evidence comes from a series of photos taken by the Mars Surveyor spacecraft. Astronomers are intrigued by pictures like this one, that shows a ravine and a crater that seems to have been altered in just the last several years by flowing liquids.

Rick Weiss of the Washington Post has been covering the story and joins me now. Welcome to you.

RICK WEISS, Washington Post: Thanks.

JEFFREY BROWN: Help us understand what scientists are seeing in these photos that suggests recent flowing water.

RICK WEISS: Well, what they’ve got is a series of before-and-after shots, some taken five, six years ago, some taken in the last year or so. And there’s remarkable differences, when they took a close look at a few of these gullies, gullies that were already there but that look very different now than they did a few years ago.

JEFFREY BROWN: All right. Here’s one we’ve just put up. So this is the before-and-after. Explain what we’re seeing. (Data and images courtesy of Science Magazine.)

RICK WEISS: Well, here you don’t have to be a rocket scientist to see you’ve got a gully here. But if you really looked with fine grain precision, as they can, you’ve got swirling patterns, moving around obstacles. You’ve got a little delta at the bottom with fingers of drainage going out.

And you can even tell by calculating the movement of how these swirls went around obstacles — what was the stuff that was going down here? Was it dust? Was it sand? Was it water? And the only thing that really fits the model with the right viscosity and so on is water, probably with some sediments.

Origins of water on Mars

JEFFREY BROWN: No one can be certain that this is water, correct?

RICK WEISS: Not yet; this is indirect visual evidence. But one thing that's very interesting, it's all white. Now, five years ago, these gullies were dark. And if you look at all kinds of damage that we see happening to Mars every day from wind or even the tracks behind the rover vehicles, those get dark when they're messed with.

These are light. It's the first time that's been seen. And the thinking is this is either frost from some of that water that has evaporated or salts left behind by that water.

JEFFREY BROWN: Is it known, or what's the theory of how the water would have -- where it would have come from, how it would have come to the surface?

RICK WEISS: Well, you know, scientists have known for a long time that there is some water on Mars, all of it seemingly frozen in the poles or as water vapor. The idea now is that there is some liquid water under the surface which creeps through cracks, gets close to the surface, probably freezes at that cold surface for a while, forming an ice dam, and then at some point, with enough water behind it, bursts through. And you have this flash flood, mini-flash flood coming out, and then drying up again.

JEFFREY BROWN: Now, mini-flash flood burst through. How much water are we actually talking about?

RICK WEISS: Well, no mini if you're right there at the time. And we're talking -- estimates are five to 10 Olympic swimming pools full of water, no small amount, rushing down, and pretty dramatic, because with the low atmospheric pressure on Mars, this water, although not warm, is going to boil. And so you've got foaming, boiling, sputtering water coming down in the thousands of gallons, and then evaporating very quickly, certainly within a day or so.

Understanding the planet

JEFFREY BROWN: All right. So as you say, we have known for some time that there is the polar ice and the suggestion that there was water in the past. So the scientists you're talking to, what's the significance they see in this?

RICK WEISS: Well, in a word, life. I mean, this the central question: Is there life or was there ever life on Mars? And the thinking until now has been, without liquid water, probably not.

In the past, clearly there was liquid water. These things were carved a long time ago. But now with the evidence that water still occasionally flows -- apparently two of these gullies flowing within the last five years -- the question becomes fresh again that, perhaps, there's a habitat here where things can live.

JEFFREY BROWN: One of the scientists was quoted as referring to this as the squirting gun, I guess playing off the smoking gun.

RICK WEISS: Right, so it is indirect evidence, but more evidence coming soon. There's a new orbiting tool kit that just arrived in orbit last month with a new kind of camera that the last one didn't have that took these shots, that's going to be able to do some chemical analysis on these white deposits to find out, is it salt? Is it frost? What's there? Which will help.

And then, in 2008, you've got a lander that's actually going to go down and land on Mars and can really check out these spots and look for evidence.

JEFFREY BROWN: Are scientists back here now able to do more than look at -- right now, they're just able to look at the photographs?

RICK WEISS: Right now, just looking at photographs, next look on the chemical analysis, and then the direct sampling after that.

JEFFREY BROWN: Now, there were also some interesting findings, I gather, about the number of craters and the recent creation of craters.

RICK WEISS: Right, this is more of the before-and-after photograph session. This is, you know, a satellite that's been taking something like 240,000 shots over the last nine years, so many of those have been re-shoots of the same area.

And that has given scientists a chance to see, hey, there's a crater here, and there wasn't one here five years ago. And by extrapolating from about the third of the planet that they've got that much data on, they've now concluded that there's about a dozen of these new craters popping up per year on Mars.


JEFFREY BROWN: And does any theory of why? And what's the significance?

RICK WEISS: Well, they are no doubt meteorite hits coming in. The significance is that this is a measure that scientists want to know to figure out how old different masses of land on Mars are. They figure the longer some mass of land has been exposed, the greater the chance it's going to get hit and get a cater.

And this gives them, for the first time, a real-time clock. Well, how many of these hits are there really per year? And have our estimates been right?

Secondarily, it's a little bit of a measure of whether there's any risk in walking around on Mars, which is something we all hope humans will be doing within the next...

JEFFREY BROWN: You mean, if we go up there, whether there will be meteors?

RICK WEISS: Whether there will be rocks falling out of the sky as we explore that planet. And the bottom line, scientists say, is with 12 a year, the odds of getting hit are low, but they're not zero, and it might be something to take into consideration.

JEFFREY BROWN: And we should just say, finally, that the craft that took these photos, the Mars Global Surveyor, has gone black. It's done.

RICK WEISS: That's right, just within the last month, went dead for no apparent reason, but it lasted seven or eight years longer than they had hoped and a lot of great information still to come from all the data sent back.

JEFFREY BROWN: And more to come from new craft.

RICK WEISS: That's right.

JEFFREY BROWN: All right. Rick Weiss of the Washington Post, thanks very much.

RICK WEISS: You're welcome.