NASA's immobilized, crippled Spirit rover likely succumbed to cold temperatures during the last Martian winter, and officials will cease attempts to regain contact with the intrepid robot this week, the agency announced Tuesday.

Artist's concept of the Spirit rover. Credit: NASA/JPL-Caltech
 
More than 14 months after last hearing from the rover, engineers at NASA's Jet Propulsion Laboratory believe the robot's internal components and electrical connections were damaged from cold temperatures in frigid Martian winter.

Temperatures inside the rover likely dipped to minus 67 degrees Fahrenheit, or perhaps even colder, according to NASA.

Spirit last communicated with Earth on March 22, 2010.

"Engineers' assessments in recent months have shown a very low probability for recovering communications with Spirit," a NASA statement said.

Officials predicted the best opportunity to hear from Spirit again would be by March of this year, when the sun was highest in the sky during the Red Planet's southern summer solstice. But repeated listening attempts and radio transmissions to Spirit resulted in no signal.

"With inadequate energy to run its survival heaters, the rover likely experienced colder internal temperatures last year than in any of its prior six years on Mars," NASA said in a written statement. "Many critical components and connections would have been susceptible to damage from the cold."

Spirit departed Earth on top of a Delta 2 rocket in June 2003 and successfully parachuted to a bouncy, airbag-cushioned landing on Mars in January 2004.

The rover accumulated 4.8 miles of driving across the basin of Gusev Crater and climbed the Columbia Hills, stopping to study numerous rocks and geologic features. Spirit ultimately found evidence Mars may have once harbored a habitable environment for microbial life.

Spirit radioed data back to Earth for more than six years, vastly eclipsing the 90-day duration of its baseline mission. The probe carried a suite of cameras, a robot arm with a tool to grind into rocks, a microscopic imager and several spectrometers to measure mineral composition.

But two of Spirit's six wheels stopped rotating, and the rover stalled out in a sand pit in May 2009. Months of analysis and extraction attempts failed to get Spirit moving again, stranding the rover on a slope with its solar panels facing away from the sun for the Martian winter.

During previous winters, NASA positioned Spirit on north-facing slopes to maximize electricity production and power critical heaters keeping the craft's internal systems warm.

Spirit's twin rover, Opportunity, continues driving across a flat plain on the other side of Mars, having racked up more than 18 miles on its odometer since landing in January 2004.

Both rovers exceeded their design lifetimes and returned much more science than expected, according to researchers.

NASA says its network of deep space communications antennas and two Mars orbiters that can relay communications need to prepare for the launch of the agency's next mission to the Red Planet in November.

The Mars Science Laboratory is scheduled to blast off Nov. 25 and land on Mars in August 2012. The mission's Curiosity rover is nearly five times heavier than Spirit and Opportunity.

"We're now transitioning assets to support the November launch of our next generation Mars rover, Curiosity," said Dave Lavery, NASA's program executive for solar system exploration. "However, while we no longer believe there is a realistic probability of hearing from Spirit, the Deep Space Network may occasionally listen for any faint signals when the schedule permits."