December 2, 2004
Spirit’s Mars Reads Like a Mystery Novel
The rovers Spirit and Opportunity have been exploring the surface of Mars for nearly a year. Principal investigator for the science package on the Mars Exploration Rovers, Steve Squyres, talks about the future of the Spirit rover and what has been learned so far from its exploration of Gusev Crater.
Astrobiology Magazine -- The rovers Spirit and Opportunity have been exploring the surface of Mars for nearly a year. Among their many discoveries, the rovers have found evidence that liquid water probably once existed on the surface of the red planet.
On November 11, Astrobiology Magazine editor Leslie Mullen talked with Steve Squyres of Cornell University, the Principal Investigator for the MER mission. They discussed what lies in the future for the twin rovers on Mars.
Astrobiology Magazine (AM): Now let's talk about the future of the Spirit rover in the Columbia Hills.
Steve Squyres (SS): With Spirit, the immediate plan is to continue to work our way up through the Columbia Hills. It's steep stuff, and tough going for Spirit partly because it's steep and partly because it's so rocky. It's a jumbled terrain full of boulders.
We're very much in discovery mode in that mission. With the Opportunity rover in Eagle crater, in our first six to eight weeks, we were in discovery mode, where every day there was some new revelation about the rocks. And that helped us to form a set of hypotheses that we could use at Endurance crater to systematically test.
Where we are with Spirit right now is sort of like where we were with Opportunity at Eagle crater. We had all that basalt out on the plains, and Spirit did its thing there, and it took us about 160 sols just to get to the Columbia Hills. But since arriving there each new rock, each new outcrop, is some new piece of the puzzle.
AM: Are you seeing stuff that you have no idea what it is?
SS: We're seeing stuff that we don't know what it is, and we think, "It could be this or that or that," and then we go to another rock nearby, and then two hypotheses are knocked out and another one pops up, and the picture becomes a little more clear. It's like a mystery novel. You get one clue at a time.
When I talk about our exploration at Eagle crater now, it sounds like we just went there and discovered all this stuff. But it wasn't like that. When we first landed, we didn't have any idea what we were dealing with, and gradually, rock by rock, clue by clue, the picture came into focus. That's where we are in the Columbia Hills right now. We now know what the texture of the rocks is like, what the mineralogy is, and we're starting to get a sense of the geology with the layerings, how much glassy stuff is there, the range of grain sizes, etc. Each one of those things is a clue.
I'm not going to hazard a guess of how long it's going to take us to climb Husband Hill, because we're going to go where the discoveries lead us.
AM: So do the discoveries direct where you go, or is it more the terrain?
SS: It's both. We're trying to be directed by the science as much as possible. We use Pancam to survey the terrain, and we'll see some fascinating rock and try to go there to start doing science on it. But we're affected by the terrain in some very basic ways. One is that there's a limit to just how steep this stuff can be. We found some rocks in the Columbia Hills that are just too steep for the vehicle to handle.
The other thing is that it's wintertime, and it's cold and dark. The sun is low in the sky. It's a really tough time of year right now at the Gusev site, but we're starting to come out of it. We're past the worst part of winter. But with the sun so low in the northern sky, we cannot park our rover on a hill that faces to the south because that will orient our solar arrays away from the sun. Then we'd be in trouble.
We make these maps that show where all the north-facing slopes are, and there'll be a little patch here and a little patch there. We call those lily pads, and we're like a frog jumping from lily pad to lily pad, staying safe as we keep our solar arrays pointed to the north.
AM: Too bad you can't really jump.
SS: Yeah, I wish we could jump! But we'll sit parked on one nice toasty north-facing slope for awhile, do a bunch of science there, and then look around and scoot over real quick to the next one.
AM: So the Columbia Hills are the entire future for the Spirit rover?
SS: They're certainly the immediate future. It's a big range of hills. It's far too large for us to totally explore with this vehicle. It turns out that the very first hill that we got to was also the tallest. Husband Hill is the largest summit in the whole range. So if we want to see as much of this sequence of stacked rocks as possible, the best thing to do is to climb to the summit of Husband Hill.
It should be a heck of a view from the top, if we ever get that far, so there's a lot to be said for that scenically as well as scientifically.
AM: And you think there's about 100 sols left in the rover to accomplish this?
SS: I really don't know. I can think of at least three things could kill us. The first is dust build-up on the solar arrays. But the dust build-up is not that bad, especially for Opportunity, and with spring approaching both vehicles should do ok for awhile.
The second thing is if something mechanical goes wrong. The rovers have a lot of moving parts, and we've seen a few mechanical funnies on Spirit. Nothing serious, but enough to catch your attention. Stuff could just wear out.
The third thing is, we've got a lot of single-string electronics in these vehicles. There's not a lot of redundancy. Now, we have the ultimate redundancy in that there are two vehicles. But within each rover there are a lot of electrical parts that, if they just flat-out fail on us, the rover's dead. Bang! It just dies overnight and never talks to us again. That could happen.
AM: When this mission finally does end, what's in your future? Are you going to spend the next couple years just analyzing data from this mission, or are you going to be working on the next Mars rover?
SS: The payload for the next rover has not yet been selected by NASA. I did not put in any proposals myself as Principal Investigator. I've done that now; I've gotten it out of my system. It's time for some other people to do that job; it's a very demanding drain on your time.
But I think we're going to be analyzing data from these rovers for a very long time. It's an incredibly rich data set. The data from the first 90 sols of both landing sites is now out there in the Planetary Data System, and anybody can access it and do science with it. To a certain extent, it's going to be very satisfying to just sit back and watch people do science with this data. We worked very hard to build these rovers, and we've worked very hard to collect the data.
But I don't think this is going to be it for me as far as Mars exploration is concerned. I'm on the imaging team for the Mars Reconnaissance Orbiter mission, which launches in less than a year. So I intend to keep doing science at Mars for a long time.
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