All attempts to extricate it have failed so far. The last time, in November, not only did the robot not budge from its place, but its right rear wheel broke down. Its right front wheel stopped working in 2006 probably due to a worn out electric motor.
Dead in its tracks, Spirit cannot shake off the Martian dust that is slowly accumulating on its solar panels, preventing its batteries from recharging.
Unless the wind blows the dust away or, in a spurt of energy, Spirit can shift its inclination to better point the panels toward the sun, "the amount of sunshine available will continue to decline until (the Martian solstice) May 2010," NASA said on its website.
That means "Spirit may not have enough power to remain in operation" during the Martian winter, the space agency added.
Despite its predicament, Spirit has been able to carry on its scientific work and has even made an unexpected discovery.
As its wheels spun and churned up the ground in its attempt to break free of the sand trap, it uncovered traces of sulfates underneath, scientist Ray Arvidson, of the Washington University in St. Louis, Missouri, said last month.
"Sulfates are minerals just beneath the surface that shout to us that they were formed in steam vents, since steam has sulfur in it. Steam is associated with hydrothermal activity -- evidence of water-charged explosive volcanism.
"Such areas could have once supported life," he said.
Spirit and its twin rover, Opportunity -- which landed on the opposite side of Mars three weeks later than Spirit, on January 24, 2004 -- have been given 90 more days of mission time.
Scientists are not too confident the Martian wind will be able to dust off their power-generating solar panels.
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