SAN FRANCISCO--The Mars rovers continue to chug along, but how long they will last is anyone's guess.
Spirit and Opportunity, the two robotic vehicles roving the red planet, have lasted more than 22 months, far longer than anyone anticipated, said scientists and program managers from the Mars rover program speaking at the American Geophysical Union, an annual conference of earth scientists taking place here this week.
Nonetheless, signs of fatigue are beginning to show. Around 10 days ago, the mechanical arm on Opportunity stopped moving. The problem, the rover teams believe, lies with the shoulder joint of the arm. If they can get the elbow of the arm out of the T-shaped housing where the arm rests, the arm can still collect samples.
"If it has failed, it will be a significant hit. It is the contact arm of the mission," said John Callas, deputy project manager for the NASA Mars Exploration Rovers project.
One of the steering actuators has also blown on Opportunity, but it can still be driven.
Spirit, which has roamed Mars for 684 days, is faring better, Callas said. The only complication right now is with the rock abrasion tool. It has worn out. Made to only take three samples, Spirit has conducted 15 rock scrapings.
Other components, however, could blow. The mission was supposed to last only 90 days, and most of the components were stress-tested for a lifetime of 270 days. With temperatures that can swing 100 degrees Celsius in a day, Mars is a tough environment for electrical components.
"We drive it every day as if there were no tomorrow," said Stephen Squyres, a Cornell University professor and the principal investigator on the rover project.
Squyres, though, added that the two vehicles have brought a wealth of information about the planet back to Earth. A climb up the Columbia Hills on Mars, for instance, has revealed an astounding variety of rocks in a small area.
"There are nine completely distinct rock types. There is a bewildering diversity," he said. In part, that's because the Martian geology was formed through meteor impacts, rather than volcanic eruptions.
Jim Bell, lead scientist for the panoramic cameras on the rover, added that the vehicles allowed scientists to take nighttime observations as well. Bell and his team have captured images of an eclipse on Mars (where the Martian moon Phobos gets obscured by the shadow of the planet) and what appears to be a meteor shower.
So far, Spirit has traveled 5.5 kilometers, while Opportunity has gone 6.5 kilometers. Together they've .
Mars, the wet planet?
Other scientists at the conference, meanwhile, asserted that the clay in Martian soil and other geological and seismic evidence points to the existence, at least sporadically, of water on Mars.
Mars likely had large bodies of water on its surface 3.5 billion years ago, but climatic changes dried up the vast majority of it, said Gerhard Neukum at the Free University in Berlin.
"Mars lost most of its atmosphere and, with it, its water," he said. Since then, "it (water) has been limited to certain periods of time, and it was local," he added.
Around 2.6 billion years ago, for instance, a volcanic explosion created a lava flow. It caused part of a glacier to melt, thereby freeing up water. The glacier, however, eventually won that contest and formed a structure called the Enigmatic Ridge, a long, straight line across the Martian surface. It was so called because scientists in the early 1970s studying the structure couldn't figure out how it got formed.
Neukum, however, said that Mars still likely has pockets of water. "We see the signature of water ice even on Olympus Mons (a humongous mountain on Mars) now," he said.
Mean-Pierre Bibring, principal investigator on the OMEGA project, which is conducting seismic studies of Mars, said that he has obtained some indications of subsurface water. The evidence is not convincing yet, but the study has just begun. More evidence will come this spring.
Bibring further added that the red color on Mars, the result of iron oxidation (rust), was not likely caused by water. It resulted from a reaction with the atmosphere.