The Mars rover Spirit's transition from operational rover to a hibernating robot will be the most dangerous period either rover has been forced to endure on the Red Planet, but it may yield a new awakening as a stationary scientific lander later this year.

NASA managers said Tuesday that the decision had been made to terminate efforts to free the rover from the sand trap where it has been captured.

An artist's concept shows a Mars Exploration Rover in its earlier days of driving across the planet. Spirit's future will be a stationary vehicle, if it survives the looming winter. Credit: NASA/JPL

They will instead try and save it from winter temperatures for use as a fixed lander for use in the scientifically-rich Home Plate region it has been studying three years. Any wheel activity in the next few days will be aimed at improving the angle of its solar array deck northward to absorb more sunlight during the dark days of winter approaching in the Martian southern hemisphere.

Spirit sits 16 degrees south of the equator, amidst the Columbia hills in the southeast area of Gusev crater.

The Martian winter will daily subject Spirit to Martian nights about minus 60 degrees F with the likelihood the rover's own self protection software will not allow "this bear to come out of its hole" until it is late summer on Earth, says John Callas, rover project manager at the Jet Propulsion Laboratory.

Only then will Jet Propulsion Laboratory and her Cornell University Athena science team know they will have, in effect, landed once again at a new landing site to carry out the rich set of fixed science objectives planned should Spirit survive.

Between now and mid February rover drivers will try and back Spirit somewhat higher on the mounds of soil behind its back wheels seeking extra degrees of solar array advantage, says rover driver Ashley Stroupe. Such maneuver last week gained 1-2 degrees more in angle toward to North. The array is clean of dust meaning with each degree in elevation, the rover could daily gain 5-6 watts of power toward an objective of 160 watt hours per day.

"In our current tilt we will see energy level drop below acceptable to keep the rover active through the winter," says Callas. The 160 watts daily would be required for the rover to maintain an Earth-in-control mode.

The rover's sensitive electronics are designed to withstand minus 40 degrees F when operating and minus 67 degrees F when not operating. They are warmed by internal electrical activity and several 1-watt passive nuclear electric heaters.

"We expect the electronics will get around minus 45 degrees C (minus 49 degrees F) in the depths of winter, Callas said.

Whether it can survive several weeks of nights with it so cold remains to be seen, says Doug McCuistion, director of Mars programs at NASA Headquarters. The rovers were built to that design specification, but that was for a brand new rover, not one six years old that has been through thousands of daily and seasonal thermal circles already.

There is no guarantee it will survive. While Spirit sleeps its science team will finish building a detailed new plan to study the complex mixture of sulfates at the site for when the spacecraft is revived, while also preparing to use the rover as a tracking beacon to calculate any wobbles in the Martian orbit that could reveal whether Mars has a solid iron or molten iron core.