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Steven Squyres is principal investigator for the Mars Exploration Rover Mission and professor of astronomy at Cornell University. The mission of the Mars rovers, Spirit and Opportunity, was supposed to last 90 days, but the robots’ endurance — more than 1,442 days at the time of this interview — has surprised everyone. Squyres will deliver a keynote speech at the April FOSE conference and exposition in Washington. : How has your relationship with Spirit and Opportunity evolved during the past four years?: When they do something good, we’re proud, and when they do something wrong, we get a little angry with them. And when they get into trouble, we worry. We feel all of these things. The worst part, of course, is going to be when the mission finally ends — when they die — and I don’t know what that’s going to feel like. I think it’s going to feel pretty bad. But they’ve lasted so long, and they’ve done so much. They’ve had far richer and more productive lives than anyone, including those of us who created them, could have ever hoped. So it’ll be an honorable death, but it will be a tough day. : If NASA develops a new breed of rovers, what characteristics would you want them to have? : The next rover is going to carry instrumentation that will enable us to look for organic molecules. On the next rover mission — the one that’s flying in 2009 — power will not be supplied by solar cells. It will be powered by plutonium. We’ve got a nuclear power source that will supply a steady, reliable source of power. This next vehicle is also bigger. A field of obstacles that Spirit and Opportunity might have a tough time picking their way through, this thing can just go monster-trucking right over it. : How have the rovers survived extreme conditions that you had not expected them to endure? : There were a few things that really helped. One was we thought correctly that we would see dust build up on the solar arrays. What we didn’t count on was that gusts of wind would periodically clean the solar arrays off. When that happens, it’s like taking the vehicle to a car wash. It just cleans it off, and power goes way up again. It’s happened three times to Spirit, and it’s happened repeatedly to Opportunity. That was just good luck. We can’t attribute it to anything other than just Mars being good to us. This is exploration. You don’t know what you’re going to get. : Would you be as interested in studying Mars and Europa if it weren’t for evidence that water existed on Mars and that Europa contains an ocean that might support life? : I would still be interested because I like planetary exploration in general. But it’s the former or maybe current presence of water on those objects that makes them special. They have greater potential as an abode for life than most of the other planets, which have far harsher conditions.