In January the Mars Exploration Rovers Spirit and Opportunity touched down, the first time since Pathfinder in 1997 that humans have had a mechanical representative on the surface of Mars. In short order the rovers found proof of past water on the planet, including minerals that can form only in the presence of water, and ripple patterns in fine-grained rocks shaped by sea currents. Steve Squyres oversees the science operations of both rovers and a team of 170 researchers at NASA’s Jet Propulsion Laboratory. He is a planetary scientist with special expertise in Mars, Venus, and the satellites of Jupiter. Squyres received his Ph.D. from Cornell University in 1981, then spent five years as a postdoctoral student at the NASA Ames Research Center before heading back to Cornell, where he is a professor of astronomy. As a graduate student, he was a member of the imaging team for Voyager’s encounter with Jupiter. Later he served as an investigator on the Magellan mission to Venus, the NEAR (Near Earth Asteroid Rendezvous) spacecraft encounter with the asteroid Eros, and the Mars Odyssey mission. He is the former chairman of NASA’s Space Science Advisory Committee.

What do you hope to accomplish with the current Mars exploration missions?

S: The objective is to learn whether Mars ever had conditions at its surface that would have been favorable to life. Mars is a cold, dry, miserable place now, but we have tantalizing clues, mostly from data taken from orbit, that suggest that in the past it may have been very different—warmer and wetter and more Earth-like. So we’ve landed in two places that might have been warmer and wetter in the past.

Have Spirit andOpportunity provided the kind of data you hoped to obtain?

S: Oh, yes, very much so.

Are you satisfied?

S: No. I’ll never be satisfied until we understand the whole planet. But it is very gratifying to have it work out this well. We went to Mars seeking evidence concerning whether or not it once had liquid water and a habitable environment, and I think we’ve found a definitive answer to that question.

What can’t the missions do that you wish they could?

S: Bring back samples. If we found some place that was really interesting and looked like it might have been favorable to life, we’d love to be able to gather up some samples and bring them back. That has to wait for a subsequent mission.

What is the most exciting result so far?

S: Opportunity’s findings at Meridiani Planum. We have compelling evidence that the rocks are made of sulfate salts, to the tune of 30 to 40 percent by weight—an enormous amount—including one mineral that requires water for its formation and actually contains water itself. What is even more intriguing about this stuff is that because the minerals precipitated from liquid water, they may preserve what was once in that water. If there was some biochemistry, if there were microorganisms present, those minerals could trap evidence of that for a long time. The best way to definitively detect that would be to bring the rocks back to a lab on Earth and take them apart.

What is the biggest surprise?

S: I’ll be honest with you: I almost feel that the biggest surprise is just how well everything is working.

You can say that after the Spirit scare?

S: That was pretty scary, but the spacecraft was in a lot less danger than it seemed it might have been at the time. It is an incredibly robust vehicle, and it really does a very good job of looking after itself. Saying I’m most surprised at how well everything is working is sort of a flip answer. Really, I think the biggest surprise has to be finding that bedrock outcrop at Meridiani Planum. It was an astonishing stroke of luck to have rolled into that crater. In my fondest dreams I sort of hoped that we might be able to find a good bedrock outcrop somewhere, but I thought we were going to have to work hard to find it.

So what else has been scary?

S: The landings, of course, were tense. I had a lot of confidence in the design, but the fact of the matter is that Mars can always get you. Our design could have functioned perfectly and still one inopportune gust of wind or one big sharp pointy rock in the wrong spot, and you’re done. I’ve got to tell you, to me the scariest parts came before we launched—when we were bursting air bags, when we were ripping parachutes, when we blew a fuse inside one of these vehicles and, as we analyzed what happened, realized that we might have a fatal flaw in the design of the pyrotechnic system. The thought that “My God, we might not even make it to the launch pad”—that was the worst.

At the beginning of the mission there appeared to be a giddy exuberance. Has the excitement worn off?

S: It has mounted. People are walking around two feet in the air. What you saw on television at touchdown was a combination of scientific excitement over what we were seeing and just pure excitement that we had landed successfully. Now it is just pure science, and if anything, the scientific excitement level is significantly higher than it was.

You seem to go out of your way to talk to the press and the public. Why?

S: This is something I feel passionate about. The American public has spent $800 million to enable this mission. I believe very firmly that those of us who have the enormous privilege to actually participate in this have an obligation to share this experience, to the greatest extent that we can, with the people who have made it possible—and to do so in a way that is not heavily laden with scientific jargon and not obscure and difficult to comprehend. We are not doing anything that is so esoteric and so complex that you can’t explain it to people in a very straightforward fashion. I think we are conducting a fantastic, fabulous, and exciting voyage of exploration and discovery, and we have all the tools that we need, via the Internet and via the media, to take the entire world along with us.

In your mind, when did the rover missions become successful?

S: I have always had two different measures of success. We have achieved one and not yet the other. This is not NASA’s definition of mission success; this is Steve’s definition of mission success. What we have not yet achieved is to work these vehicles and these payloads so successfully that we have learned everything we are capable of about the places where we touched down. The other measure of mission success was getting 12 wheels in the dirt with two healthy payloads. It was such a rough ride to get these missions built. Technically, these were incredibly challenging spacecrafts to build and deliver. What the team here at the Jet Propulsion Lab pulled off was astonishing and magical.

Can we answer all our questions about Mars with unmanned robotic missions, or do we need to send people?

S: We need to send people. There is nobody who is a bigger fan of sending robots to Mars than me. That is what I do. But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans. Maybe you can argue that if you spend enough time and effort and money on robotics, eventually they’ll be able to mimic human capability, but I think we are so far from that that ultimately sending humans would be the right thing. The sooner the better, as far as I’m concerned.

So why not skip all these incremental robotic missions and throw that money into a dedicated program to send humans to Mars?

S: There are two answers. One answer is that it makes sense, before you commit the enormous resources necessary to send humans, to learn enough about the planet so that when humans get there they can use their precious time and capabilities most effectively. Mars is an incredibly diverse and complicated place. If you have to pick one place to put humans down, where is the best place? If you pick wrong, you’ve wasted a lot of money. So it makes a lot of sense from a scientific standpoint to do precursor missions. Secondly, there is the simple reality that sending people to Mars will require an enormous amount of political will and commitment of national, and probably international, resources. If we’re not ready to do that yet, the way to make progress toward that goal is to explore the planet robotically.

Do you think we will find evidence of life, past or present, on Mars?

S: I don’t have an opinion on that. In fact, I believe firmly that the worst thing a scientist can do is to have a preconceived notion about what you are going to find because it can skew your interpretation of the data.

On a philosophical note, what does it matter whether or not there is life on Mars or somewhere else in the universe?

S: You’re right, it is a philosophical question. If I can’t convince you that learning whether or not life is common in the universe or that learning how life came about is an interesting fundamental problem that people should care about, then nothing else I say is going to make any sense. If you do accept that premise, looking for whether or not there was ever life on Mars is important in two ways. Right now we have one example of life: us. We are it. If all you have is one example of something like this, you have no way of knowing how common, how rare, how unique it is throughout the universe. But if we were able to show that life had arisen independently on two different worlds, just within this one solar system, the idea of it being common throughout the universe is an easy one to accept. That is one reason. The other concerns the question of how life begins. You’d love to actually find evidence of that event in the geological record, but on Earth the early record was destroyed by volcanic and tectonic processes. You don’t find 4.3-billion-year-old rocks here. Yet literally half of Mars is covered with rocks that old. So if—big if—life ever arose on Mars, not only could we find out, yeah, there is life somewhere else in the solar system, but the record of how that miracle occurred would still be preserved in these ancient rocks. If you want to know how life first arose, Mars might be the place to get an answer.

Carl Sagan was a close colleague. What do you think he’d say about these missions?

S: I think he’d think this mission was a hoot. I think he’d want to be here with his sleeves rolled up, having fun going through the data like the rest of us.

How did you get interested in planetary science?

S: Back when I was an undergraduate student at Cornell, I went into geology because I liked to do science and I loved to climb mountains, and geology seemed like a good way to combine those two passions. After a few years, I came to realize that the geologists who have studied this planet had actually done a pretty good job of it, so to a certain extent studying the geology of Earth felt to me like filling in details. Then in my junior year I signed up for a course being taught by Joe Veverka, who is now chairman of the department. He was on the Viking Mars mission science team in 1977 and was teaching a course on the results. That course really changed my life. Because it was a graduate-level course, we were supposed to write some piece of original research. There was a room where they kept all the pictures from the Viking missions—this was before the Internet, CD-ROMS, and all that stuff—and a few weeks into the course I went to look at the pictures, figuring I’d flip through them for 15 or 20 minutes to try to figure out what I would write my term paper about. I was in that room for four hours. I walked out knowing exactly what I wanted to do with the rest of my life. Here was this whole world that no one knew anything about, and it wasn’t filling in details: It was a very big blank canvas. That was it.

Why do you personally study Mars?

S: Because among all the planets, it is the one world where we can imagine life as we know it taking hold. The other solar system body that has always intrigued me, for the very same reason, has been [Jupiter’s moon] Europa. Europa has enormous appeal to me, but addressing the water and life problems there would require submarines, versus rovers on Mars, which is something I can do now.

What is it like working on Mars time? Do you feel disconnected from the world?

S: Getting into Mars time is tough. The way it works is that the Martian day is 24 hours and 39 minutes long, and so if today’s science operation working group meeting starts at noon, then tomorrow’s will start at 12:39, the day after that, 1:18, and 2 1/2 weeks from now it will be in the middle of the night. So if you are on Earth time and you have to suddenly jump to Mars time, you can get a wicked case of jet lag, which can be mild or terrible depending on when you do the jump. What is really rough is changing rovers, because they are on opposite sides of the planet and so are 12 hours apart. It is like getting on a plane and flying to India.

That having been said, once you get yourself in the groove and sync yourself with Mars time, it is not that hard. You get to sleep an extra 39 minutes later every day. Maybe that’s hard if you’re a morning person, but getting a little extra sleep each day feels good to a night owl like me. When it becomes tough is when you are trying to do the Mars time thing and the real world intervenes. For example, right now it is almost midnight Pacific time, but it is 9:30 p.m. at Meridiani Planum. My shift normally ends a little after midnight Mars time, so I get off work about three hours from now. But unfortunately a very important meeting having to do with long-term planning, budgets—stuff that I need to worry about—has been called for 8 o’clock Pacific time tomorrow morning, right in the middle of my night.

What are you working on after this mission

S: Getting some rest and spending a lot of time with my family. I am a member of the imaging team for the Cassini mission [which will arrive at Saturn in July]. My goal for planetary missions from here on out is to find roles where I can have a lot more fun and a lot less responsibility. Actually, no, I can’t imagine having more fun, but a lot less responsibility.

What is the biggest challenge of your job?

S: I think the biggest challenge is trying to balance all the competing desires among the science teams. I’ve got 170 people on my team, split into two groups, one working on each rover. On any given sol [Martian day] you’ve got 50 people working on a given rover. Of course everyone has their own interests and their own ideas about what we should do next, so I have to find the best ideas and build a consensus around them. You never want to have the person leading the science team be a dictator. And you can’t just think tactically—think this sol, and the next sol, and the next, one at a time. It all has to be part of a sequence that makes sense strategically.

If we didn’t have such an enormously flexible and capable vehicle, this would be fairly easy. But these rovers are like Swiss army knives, with so many tools and so many capabilities, that finding the way to get the optimum usage, given all the constraints and all the desires and all the science you want to do, is a wonderful challenge to try to meet every day. It is like nothing I have ever experienced before. It is intricate, it is fascinating, and it is an incredible amount of fun.

Do you know the final date of the rover missions, when it all ends?

S: It ends when the last rover dies. We had an advertised design lifetime of 90 Martian days per rover, but I think they will last a lot longer than that. Twice that is possible. We will work ’em as hard as we can until they are both dead.

And then?

S: At some point, you just pack up and go home. But we are generating an enormously rich data set. I have no idea how many scientific papers, how many scientific careers, how many Ph.D.’s will come out of this mission, but there are going to be plenty. So, yeah, we’ll pack up and go home, and that will be both a wonderful and a very sad day, but milking the data for everything in it will take a long, long time after that.