After six years of roaming the Red Planet, the Mars rover Spirit's travelling days are over. But if it survives the upcoming Martian winter, it could be used as a stationary research lab to help study the planet's interior.
Spirit has been stuck in a patch of soft, sandy soil since April 2009. After months of testing escape manoeuvres with two mock rovers on Earth, NASA began attempts to extricate Spirit in November 2009.
But progress has been painfully slow. The rover's three left wheels are almost entirely buried and have little traction, and two of its right wheels are broken and must be dragged or pushed.
Now, NASA has given up hope of freeing the rover. "We do not believe it is extractible," said Doug McCuistion, director of NASA's Mars exploration programme, at a press briefing on Tuesday.
The rover's useful life may not be over, however. NASA has designated Spirit a 'stationary research platform', and if it survives the six-month winter, which will peak in May, its first priority will be to transmit radio signals that can be used to pinpoint its location in space.
Over time, these signals could help researchers discern subtle wobbles in Mars's rotation, which could help reveal whether the planet has a solid or liquid core.
The rover could also track how Martian winds transport dust across the planet and could perform more detailed measurements of its sand trap, which may once have been part of a hot, watery landscape filled with steam vents.
But it is far from clear whether Spirit will make it through the southern hemisphere's fast-approaching winter. In past winters, the rover has driven onto north-facing slopes to maximise the sunlight falling on its solar panels. But Spirit is currently tilted in the opposite direction – some 9° to the south.
That orientation may not be enough to power the rover through winter, so NASA is working to tilt the rover northwards by rotating and turning its wheels. But waning sunlight means the solar-powered rover may have just three weeks to attempt the manoeuvres.
If it can't tilt itself northward, Spirit will likely enter a state of hibernation, turning on briefly each day to check the status of its batteries before powering down. "We have to be prepared to go through a period where we're not hearing from the rover for an extended length of time," said John Callas, rover project manager at NASA's Jet Propulsion Laboratory in Pasadena, California.
Spirit's survival will depend on its ability to stay warm. The team estimates that temperatures in the area will descend to some -45 °C during the winter. That may be warm enough for the rover's sensitive electronics, which were designed to operate down to a temperature of -55 °C. The electronics will also be warmed in part by small heaters that run off the decay of radioactive elements.
But after years on Mars and "thousands of gruelling temperature cycles", there is no guarantee that the rover will be able to survive the winter cold, Callas said. If Spirit does, it may be August or September before it has sufficient power to communicate regularly with Earth, Callas said.
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