Robert Barker/University Photography

Steve Squyres is pictured lecturing on the Mars mission at Goldwin Smith Hall last spring. In a July interview, he called the past few months "the most exciting and rewarding period of my career."

Steve Squyres, Cornell professor of astronomy and the principal scientific investigator for the Mars rover mission, has become a familiar figure to much of the nation since two rover vehicles bounced down on the Martian surface last January -- Spirit in Gusev Crater and Opportunity on the opposite side of the planet on Meridiani Planum. Squyres took a break from his hectic schedule this July to talk to Cornell News Service Senior Science Editor David Brand about the progress of the history-making mission.

When the two rovers landed on Mars in January did you believe they would still be going strong?

I had hopes. But I wouldn't say I had anything like confidence they would last this long.

Realistically, how long will they last? Into next year?

It's possible. It's possible. The key question is whether we make it through the Martian winter or not. If we make it through the Martian winter, and the depths of winter come around in late September on Earth, and if we make it through that and the sun starts coming back south again, things will start getting better.

What are the constraints on the rovers' longevity?

Three different things could do it. One would be mechanical systems giving out. Or we could have some electronic part fail. There are a lot of single-string, that is non-redundant, aspects to this design and there are some components that if they fail, then we are just done. And the third possibility is dust buildup on the solar arrays, plus the effects of the changing seasons will get us. If it's the dust buildup on the arrays and nothing else and we make it through the winter, we could be good for a while after that.

How does dust buildup affect the solar arrays?

Inevitably they will become coated with so much dust that they will not produce enough power. We need to have enough power to be able to recharge our batteries daily so that we can use electrical power from those batteries at night to keep things warm enough inside the rover so that we can do our daily communications activities and basic engineering functions. There is some minimum keep-alive energy that you've got to get every day and once it drops below that number, you're done.

Is the evidence now incontrovertible that water once existed on Mars in lakes and inland seas?

Well, it was before we landed. You've got to realize that what we were trying to do was not try to prove that there had once been water on Mars. Mariner 9 in 1971 discovered clear evidence that water once flowed across the Martian surface. What we were seeking was rocks that were actually formed in liquid water so that we could read the record in those rocks, not just to say liquid water was on Mars but to learn something about what the environmental conditions were like, would they have been suitable for life and, importantly, do the minerals that were formed have the capability to preserve for long periods of time evidence of former life? That's probably the single most important thing we have found: evidence for minerals at Meridiani that are the kinds of things that are very good at preserving evidence of ancient life for very long periods of time. So that we need to bring materials back from a place like Meridiani and put them in the best laboratories on Earth and let scientists pick them apart practically molecule by molecule. We've answered the question, Was it habitable? Yes, it was. But was it inhabitated? Different question. To answer that you've got to bring the rocks back. But we know where to go now.

What are the chances of the mission finding evidence that microbial life once existed?

It's not designed for that. And it never was something we intended to try to do. It's a mission about habitability, whether or not the conditions were right for life.

But is there proof it was habitable?

We have compelling evidence that would stand up before a jury of our peers: at a particular place and at a particular time. Mars has been a very harsh place over much, probably most, of its history. But there was a place and there was a time on Mars when the conditions were such that they would have been suitable for life.

And when was that time?

I don't know. I don't know how long it lasted either.

How high into the Columbia Hills will Spirit climb?

I don't know. We will try to climb as far as we need to find the things we are seeking, including stuff like bedrock. We still have never touched bedrock in Gusev Crater. We've seen lots of bedrock in Meridiani, but none at Gusev. But we see it up the hills now. So we will go as far as we need to try to get to bedrock if in fact the hills are climbable. We don't know that they are, we haven't tried yet. We could have a very hard time getting up these hills. The power situation is getting poor. We have a wheel on Spirit that may be about to fail. This thing has been driven five times farther than it was ever designed to go. So it's getting pretty beat up and worn out. Plus the hills may simply be so steep and composed of such loose debris that the rover slips too much and we can't get up them. So I don't know if we will be able to climb the hills, let alone how far we can go.

And on the other side of Mars, how deep into the crater will Opportunity descend?

On this particular foray into the crater, which may be our last and may not be, we are going to go either until we get to some place where the terrain is so steep we may not be able to get up it, or until we simply run out of bedrock. I don't know which of those two it's going to be, but I think it's going to be the latter. The slopes look pretty moderate all the way down, but you get deep enough down into this thing and you go from intact bedrock into jumbled-up stuff and soils. So once we get to the point where either we can't go any farther or its not scientifically productive to go any farther, at that point we will shoot back out of the crater and go to do some more work out on the plains.

Is there a possibility that Opportunity will be unable to climb back out of the crater?

I don't think so. Given the terrain that we've traversed so far, we have a very high degree of confidence that we will safely climb back out. Part of the reason we are so confident is that we have been doing it as we go: We'll go in two steps, then back one. These little uphill drives have happened with very little slip. This thing is a heck of a good hill climber, as long as you are on rock.

Do you believe there are more exciting discoveries ahead for the two rovers?

Yes I do, especially at Gusev. At Meridiani I think the most important discovery was made in the first 45 sols after we landed, that remarkable month and a half in Eagle crater. Now what we are doing is much more in-depth exploration to try to bring the basic story that we put together there into better focus, to learn more details, to fill in the gaps in our knowledge. But the fundamental story I think we have got pieced together pretty well. At Gusev the first 155 sols of the mission were on materials that were not what we went there looking for. Then we had this remarkable 3-kilometer drive, trudging across the plains day after day after day and we got to the Columbia Hills, and thank goodness they were something totally different and wonderful. We don't have that story pieced together yet, it's like being back at Eagle crater again, it's fantastic. So I think there's potential for a lot more at Columbia Hills.

Will Cornell be a major participant in the next Mars mission?

The next Mars mission is an orbiter that will launch next summer, and yes, Cornell will definitely be a participant in that one, though not in the leading role that we're in on the current one. After that, it's a little less clear. The next major NASA Mars rover mission is scheduled for launch in 2009. All I can tell you is that I will not be principal investigator. This has been an enormous amount of work. It has been a huge amount of time away from my family. I just cannot ask my wife and my daughters to make that kind of sacrifice again. So this is my last stint as PI, for sure.

There are reports that the Mars mission is moving to remote operations.

We are hoping by the end of August or the beginning of September we can all come home. Right now I'm living in Pasadena and visiting my family in Ithaca for a few days each month. I hope to invert that. I hope to be living back home with my family and visiting JPL a few days a month.

So everything can be done remotely?

By the end of August I expect that it will. We're gradually putting into place all of the teleconferencing, videoconferencing, remote computer hookups and everything that is necessary so that we can do fully remote operations. The objective is to be completely ready to move to that mode of operations by the end of August. I'll be functioning out of the fourth floor of the Space Sciences Building at Cornell. The science operations working group meeting will be run from there.

How would you characterize these past few months?

It has certainly been the most exciting and rewarding period of my career. It has been satisfying at every level, from being a thrill to come to work in the morning to being a culmination of 17 years of effort. It has been truly remarkable.