A Thousand Days on Mars

Oct. 26, 2006 — -- From the start -- from the day the first of the two Mars rovers safely landed there in 2004 -- Steve Squyres has been warning that their time was limited.

At some point a computer would crash, or a circuit would give out, and one rover or the other would die.

It hasn't happened. The two robotic rovers were supposed to last for 90 "sols," or Martian days. As of today, Spirit, the first rover, has survived 1,000 sols.

"It's pretty amazing, actually," said Justin Maki, the lead imaging scientist for the rover project. "The rover's basically in good health, especially considering its age."

It hasn't been easy. In the summer, the daytime temperature may rise above freezing, but much of the time it is more than 100 degrees below zero.

The air is thin -- but not too thin to deposit a fine layer of dust on the rover's top deck of solar panels, lessening their ability to turn sunlight into electricity.

And the rovers are wearing down. Squyres has said the temperature swings are hard on electric motors and computer circuits.

"All that expansion and contraction, freeze-thaw, freeze-thaw, freeze-thaw -- something's going to pop," Squyres said last year in his office at Cornell University, back when Spirit had survived "only" 575 sols.

Squyres, the principal investigator for the rover project, still commutes when necessary between Cornell, in central New York state, and NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Perhaps the biggest inconvenience is that Spirit's front-right wheel has stopped working. When engineers command the rover to move, they tell it to go backward, dragging the bad wheel behind it.

In fact, though, Spirit hasn't moved in about 200 days. It is currently winter in the southern hills it has been exploring, and the sun is low on the horizon.

Engineers strategically parked it on a slope facing north, so that its solar panels would get more energy.

They get very little unless the sun shines almost directly down on them.