NASA's Spirit Mars rover could be facing the prospect of freezing to death after attempts to free it from a sand trap suggest it may now have two disabled wheels.
Spirit got bogged down back in April, and its three left wheels are almost completely buried. Its right-front wheel clapped out in 2006, and the right-rear wheel is also showing signs of failure.
NASA first tried to budge the vehicle on 16 November, following ground-based tests using a dummy rover and sandbox. During the first couple of attempts, the right-rear wheel spun a bit before "unexpectedly stopping", as New Scientist puts it.
Spirit was commanded to spin the wheel again on 3 and 4 December, but it "did not budge". This lack of motion was described as "troubling" by John Callas of NASA's Jet Propulsion Laboratory.
He said: "It was questionable whether we could get a five-wheel-driving rover out. If we have a four-wheel-driving rover [with] only one driving wheel on the right-hand side... then extracting the rover from its current embedded location is unlikely."
The upshot of that would be a slow death for Spirit "if it remains stuck when winter arrives six months from now at the rover's location in Mars's southern hemisphere".
NS explains that the rover previously "rested on slopes that angled its solar arrays in a way that captured as much sunlight as possible". This enabled the vehicle's heaters to protect the electronics from freezing.
Spirit's current position is not so hospitable, and dust is gradually accumlating on the solar panels, adding to concerns the rover is doomed.
Callas said: "If we extrapolate current dust accumulation rates out to the next winter six months away, it does look troubling. There's a real possibility Spirit would not have power to survive the winter at its current attitude."
NASA hasn't thrown in the towel yet, though, and the agency is currently pondering what might have happened to the right-rear wheel. Possibilities include motor failure, internal gearbox jam, or external jam (a rock in the wheel, for example).
It concludes: "Commands being developed for Spirit's activities on sols 2109 and 2110 (Tuesday and Wednesday, Dec. 8 and 9) will include more diagnostics to explore these hypotheses." ®