Attempts to free trapped rover Spirit from a Martian sand pit have failed, but as one chapter of exploration ends, another is only just beginning.

“Spirit is not dead; it has just entered another phase of its long life,” says Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters in Washington. “We told the world last year that attempts to set the beloved robot free may not be successful. It looks like Spirit’s current location on Mars will be its final resting place.”

Spirit, and its twin rover Opportunity, have been exploring the red planet for six years this month, on a mission that was only designed to last 90 days. Spirit ran into trouble nearly ten months ago while driving along the western edge of a low plateau known as Home Plate, its wheels becoming embedded in soft sand.

With one of the rover's wheels redundant since 2006, trying to rescue Spirit was especially challenging, and it became ever more embedded in the sand trap. Now the rover faces another challenge: winter. The rovers are solar powered, but by mid-February Spirit will have limited power. In the meantime the engineering team will use the remaining power to improve the rover's tilt, which is currently angled to the south. Since the winter Sun remains in the northern sky, decreasing the southward tilt will boost the amount of sunshine falling onto the arrays, thus prolonging the rover's lifetime further.

“We need to lift the rear of the rover, or the left side of the rover, or both,” says rover driver Ashley Stroupe. “Lifting the rear wheels out of their ruts by driving backward and slightly uphill will help. If necessary, we can try to lower the front right of the rover by attempting to drop the right-front wheel into a rut or dig it into a hole.”

Just a few degrees improvement to the current tilt would enable Spirit to keep communicating with the Earth – via Mars orbiters which act as relays – through the Martian winter. “Getting through the winter will all come down to temperature and how cold the rover electronics will get,” says project manager John Callas. “Every bit of energy produced by Spirit’s solar arrays will go into keeping the rover’s critical electronics warm, either by having the electronics on or by turning on essential heaters.”

Spirit may have found its final resting place, but a new era of research beckons. “There’s a class of science we can do only with a stationary vehicle that we had put off during the years of driving,” says Steve Squyres, principal investigator for Spirit and Opportunity. “Degraded mobility does not mean the mission ends abruptly. Instead, it lets us transition to stationary science.”

Not wasting any time, Spirit has already begun contributing data to studies of the tiny wobbles in the rotation of Mars to gain insight about the planet’s core. This is a long term project, requiring months of radio-tracking the motion of a point on the surface of Mars – i.e. Spirit – to calculate long-term motion with an accuracy of a few centimetres. “If the final scientific feather in Spirit’s cap is determining whether the core of Mars is liquid or solid, that would be wonderful – it’s so different from the other knowledge we’ve gained from Spirit,” adds Squyres.

Spirit will also continue to study the soil in which it is embedded, watch how the wind moves soils particles around the surface and monitor the local weather conditions.