Mars Rovers Mark Fourth Anniversary

WASHINGTON — The remarkable Mars rovers are beginning their fourth year surveying the surface of the Red Planet.

"NASA's twin Mars rovers, nearing the third anniversary of their landings, are getting smarter as they get older," the space agency said last month in preparing to mark the third anniversaries of rovers Spirit and Opportunity. Spirit began its fourth year on the surface on Jan.3; Opportunity reach the same milestone Wednesday (Jan. 24).

The rovers have far exceeded their projected lifetimes on the frigid surface of Mars, uncovering evidence of recent water flows on the surface and other unprecedented scientific observations. Opportunity has most recently been prospecting around a deep impact crater called Victoria Crater.

Project managers at NASA's Jet Propulsion Laboratory (JPL, Pasadena, Calif.) said Spirit has recently photographed dozens of "dust devils" on the Martian surface.

The rovers are currently testing their ability to perform four new tasks included in revised flight software recently uploaded to onboard computers. One would enable the rovers to examine images and recognized certain types of features. Another, called "visual target tracking," would allow the rovers to stay focused on a designated landscape feature while moving.

Project managers said the new software could give the rovers greater autonomy.

"Before this, the rovers could only think one step ahead about getting around an obstacle," said John Callas, project manager for the Mars Exploration Rovers at JPL. "If they encountered an obstacle or hazard, they'd back off one step and try a different direction, and if that direction didn't work they'd try another, then another. And sometimes the rover could not find a solution.

"With this new capability," Callas added, "the rover will be smarter about navigating in complex terrain, thinking several steps ahead. It could back out of a dead-end cul-de-sac. It could even find its way through a maze."

Opportunity has so far logged 5.7 miles on the surface. Spirit has traveled 3.7 miles. Scientists credit their unexpected longevity to power conservation, a rugged design and "conservative" software programming that allows the rovers to question or even refuse commands they interpret as dangerous.