NASA - National Aeronautics and Space Administration

Q: It's a tough life in one Martian neighborhood. I'm Jane Platt and you're listening to a podcast from NASA's Jet Propulsion Laboratory in Pasadena, California. Joining us from New York is Dr. Steve Squyres of Cornell University. He's the principal investigator for the science instruments on the twin Mars Exploration Rovers, Spirit and Opportunity. The rovers have been on the red planet now for nearly two years. Steve, your team has conducted the most thorough analysis yet of Opportunity's discoveries in the Meridiani area. What have you found? Basically, what's new on Mars?

Squyres: Well, what's happened is because of the longevity of the rovers, because they've been able to explore for so long, we've been able to really add new layers of understanding to our knowledge. When we first landed with Opportunity in Eagle Crater, we landed in a small crater only about 60 feet in diameter. We spent about two months in that crater and we learned a fair amount there, but by going out of the crater, by driving for long distances and then by descending down into another much larger crater called Endurance, we were able to see much deeper into the Martian crust and see layers of rock that we hadn't seen before, and those really enriched our understanding of the whole story

Q: Ok, and what do you now know? You have a new batch of science papers about the area you've been studying with Opportunity. Explain briefly what you found.

Squyres: Well, what we found is that this was a place where there was once water on Mars. The water was primarily beneath the ground. The water was not nice, pure water, it was salty stuff, and it was probably very acid. It was probably sulfuric acid. And what happens is this sub-surface water, think of it as a water table. It goes up and down and sometimes it would rise to the surface, and when it rose to the surface it would evaporate away and leave sulfate salts behind. And then those sulfate salts would blow around in the Martian winds and form dunes. And we see evidence of these dunes, we see evidence of water soaking the sub-surface, and we see occasional evidence of water coming to the surface. But it was a pretty dry place much of the time with most of the water beneath the ground.

Q: So basically it sounds like a not very friendly area for potential formation of life?

Squyres: Well, that's hard to say. I mean you can go to places on Earth that are arid, you can go to places on Earth where the water is acid, and they're teeming with life. So it was an environment that would have been suitable for some forms of life, but it would have been a challenging one. And it particularly would have been a challenging one, we think, for life to first take hold. It might have not been a good place for life to first have been born. I'm hoping that one thing that will come out of this work is that people will take a closer look at what kinds of conditions are necessary for the origin of life and whether it might first be able to take hold under these conditions. But it was not a particularly nice place.

Q: I want to ask you more about the potential implications, but first I wanted to ask you about a statement you made. The latest findings that you're talking about are contained in a batch of science papers, and you're calling them the most significant you've ever published. What is so significant about them?

Squyres: Well, it's the first publications in which we've really been able to lay out all of our results in detail. When we first made these discoveries in Eagle Crater when we first landed, we published a batch of papers. They were very short. The paper that described all the interesting stuff in the rocks was about four pages long. This volume of papers is about 200 pages long, and it contains a great deal of information both going into our findings in much greater scientific detail and also adding data from many hundreds of days of exploration, as opposed to just the first couple of months.

Q: And getting back to these specific findings and how you came to these conclusions, there were two avenues you followed in coming to these conclusions. Let's talk first about the studies you did of the rock layers.

Squyres: Yeah, it's what geologists would call stratigraphy, studying the layering in the rock and what it has to say about conditions. We were able when we went down into Endurance Crater with Opportunity to go down what geologists would call a stratigraphic section. This was almost 25 feet of rock that we were able to work our way through. Think of a horizontal stack of layers that we were able to work our way down through. And what we found was that the conditions in the rock were very different in the different layers. In the bottom-most layers of the stack of rock, what you find is evidence for sand dunes. Now the dunes, the sand grains themselves are made largely of salt. So this is, these are sand grains that formed when water came to the surface, evaporated away, left salt behind, and then the salt blows around to pile up to form dunes. Then you go higher up and you get into what geologists would call a sand sheet. Again, this is grains of sand that are blowing in the wind, and then only in the very uppermost layers, only in the top couple of feet really do you find evidence of water actually coming all the way up to the surface and flowing across the surface and making ripples. So we were able to put together kind of a sequence of events, dry at first and then becoming wetter as you went upward through the geologic section.

Q: And the significance of that particular piece of the puzzle?

Squyres: Well, what it does is, it gives you a richer picture of what the conditions were really like. If all you have is that last little top bit where you see evidence for surface water, you could be led to conclude that surface water was around most of the time. You just simply don't know. When you have that much deeper, much richer record, what it says is that at the surface it was dry most of the time, and the water would only rise up to the surface occasionally. So most of the water story here is actually water beneath the ground, and it only occasionally comes to the surface.

Q: And what about the composition of the rocks? You studied that as well.

Squyres: Yeah, that was key. What we were able to do is not only just verify what we had concluded previously about the composition, but really enrich our understanding. What we had learned a long time ago was that there are basically three components to this rock. There's a mineral called hematite. It's an iron mineral, an iron oxide. There is salt, sulfate salt, and that makes up roughly 40-percent of the rock or so, and then the rest of the rock is fine-grained, highly altered. Think of it as dust basically, very fine-grained dust or soil type material that has had its chemistry changed considerably by interacting with water over time. And we find these materials mixed together, but as you go deeper down into the carter, the mix changes. And what you find is that as you go deeper down, some of the salts have been dissolved away. You see much more of the other components and less of the salt as you go deeper, and less of the sulfate salts. And that's because the rock down deep has been soaked with water for a considerable amount of time and much of the salts eventually dissolved away. And so we see gradients in composition, changes in what the rock is made of as a function of depth, that tell us something about how things have changed over time.

Q: So based on the study of the composition and the rock layers, the structure of the rock layers, can you tell me how you would sum up what you now believe about that area and its water history and the potential for the formation of life--or not?

Squyres: Yeah, it was a place where there was water beneath the ground, the water was probably very acid, it was probably sulfuric acid, the water table fluctuated, it would go up and it would go down. We don't really understand what caused the water table fluctuations, but we see very, very clear evidence for it. Sometimes the water would rise all the way to the surface and you would actually have exposed water at the surface that might have lasted only for a very short period of time, and the water would evaporate away and leave salts behind. These sulfate salts would blow around in the wind and form the dunes and so forth that we see preserved in the geologic record. It's the kind of place that had all the necessary ingredients for life, but it could have been a challenging sort of place for life to take hold.

Q: And what does this tell you in the big picture of what you've learned over the last nearly two years with the rovers about, has it changed your thinking at all about the existence of water on Mars, and the history of water on Mars?

Squyres: Well, what it's told us is that Mars is a place where there was water, there was water beneath the surface. We haven't found any evidence for waves, we haven't found any evidence for deep water, we haven't found any evidence for rainfall. That doesn't mean none of those things happened. But what we have found has been evidence for a much more limited sort of water activity where water just comes to the surface for brief periods. It could have been very different on other parts of the planet. One thing to keep in mind is that Mars is an incredibly complex and geologically diverse place. It would be very risky, I think, to try to draw too many planet-wide conclusions from one or two little spots on the Martian surface. I think there's a much richer story out there to be told.

Q: What's next for Opportunity and for Spirit that might help tell you more about these issues?

Squyres: Well, with Opportunity, we'd like to see even deeper into the crust, we'd like to find an even bigger hole to climb down into, or we'd like to find a place where we can climb up into higher layers. Basically, what we've got now is we've got about 20 to 25 feet of this stack of rocks that we have examined in detail. I'd like to double that, triple that, quadruple that. And in order to do that, you have to go other places.

Q: Well, we'll find out how Steve Squyres and the other Mars Exploration Rover scientists hope to achieve that goal in Part 2 of this interview. It will be available online next Monday, Dec. 5 at NASA.gov In Part 2, Squyres will talk about the one Martian-year anniversary of the rovers, which translates into nearly two Earth years. The rovers in that time have been a lot of places and learned a lot of things. We'll talk about all that next week. And in the meantime, more information on the rovers is online at NASA.gov. Thank you to Dr. Steve Squyres of Cornell University. And thanks to everyone who joined us today for a NASA/JPL podcast.