One of the two U.S. robot rovers on Mars has developed a problem in one of its six wheels. Ground controllers do not know how long the wheel will operate, but say it should not prevent the machine from continuing to roll along.
After five months on Mars, the U.S. rover "Spirit" is suffering from age. Since landing in January, it has traveled a little more than three kilometers searching for signs that water once flowed on the red planet, but mission manager Mark Adler says the motor in Spirit's right front wheel is consuming three times more power than it should. He says this indicates there is resistance in the gears that transmit motor revolutions into turns of the wheel.
"We joked in the past about being past warranty on these rovers and now we're actually seeing some signs of being past warranty," he noted. "We're starting to see some real degradation. They were designed for a three-month lifetime. They are already now two months past that, five months into their bonus time mission. As we've said before, these rovers could continue to operate for several more months or they could stop and fail tomorrow. We don't know."
Mr. Adler says the rovers were designed to roll on as few as three or four wheels, which have enough power to push the machine along on fairly even terrain. Missing only one wheel would apparently allow it to continue to roll over rougher terrain.
Spirit has arrived at the base of the Columbia Hills to explore rock and other geological formations for evidence of ancient water. The U.S. space agency NASA says water is a sign that life could have once existed on the planet.
The twin rover "Opportunity" has found evidence that a salt-water sea existed on the other side of Mars and is now seeking further clues in a deep depression called Endurance Crater. Mission controllers had feared that the steep angle of the crater's rock-strewn slopes might prevent Opportunity from having enough traction to back out and explore other areas, but Mr. Adler says the rover's performance has allayed that worry.
"We've been seeing exactly the slippage that we've expected and we've gone into the crater, gone back out, and gone back in again to make sure that we can do that," he said. "Right now we have no reason to believe that we are not able to traverse the crater and we're continuing down into it."
Mission officials describe remarkable rocks observed in the past few days by the Spirit rover at the Columbia Hills, formations they say look like rotting loaves of bread and cobra heads. They are rocks that have slid down the side of the hills.