NASA's aging Spirit Mars rover, stuck in loose soil and forced to endure the harsh Martian winter with reduced solar power, has not phoned home since March 22. Officials warned Friday that "a miracle" may be needed to restore the rover to limited operation.
, Spirit was unable to orient itself to maximize solar-power levels before the onset of its fourth winter on Mars. Engineers expected the rover to put itself into electronic hibernation, suspending communications and conserving power to warm and recharge its batteries and to run an internal clock.
The rover is programmed to take itself out of hibernation and call home whenever the batteries are sufficiently charged. But if the batteries lose too much charge, and if the internal clock stops ticking, the rover's computer could re-awaken but not know what time it is.
In that case, known as a "mission-clock fault," the Rover's computer would start a new clock, waking up every four hours during daylight to listen for signals from Earth. In a best-case scenario, Spirit could have started listening as early as July 23.
Starting July 26, engineers began sending commands to Spirit, ordering it to phone home if possible. But analysis of available sunlight and the cold environment indicates the rover may not be able to respond until late September to mid-October. That's assuming it's able to respond at all.
"It will be the miracle from Mars if our beloved rover phones home," Doug McCuistion, director of NASA's Mars Exploration Program, said in an agency statement. "It's never faced this type of severe condition before--this is unknown territory."
Winter on Mars runs from May through November. During past winters, heaters kept Spirit's internal temperatures above minus 40 degrees Fahrenheit. This time around, most of the heaters are not powered and temperatures could go as low as minus 67 degrees.
Whether Spirit can survive is an open question.
"This has been a long winter for Spirit, and a long wait for us," Steve Squyres, the principal investigator for the Mars Exploration Rovers at Cornell University, said in the NASA statement. "Even if we never heard from Spirit again, I think her scientific legacy would be secure. But we're hopeful we will hear from her, and we're eager to get back to doing science with two rovers again."
Spirit and a twin rover, Opportunity, landed on opposite sides of Mars in January 2004. Designed to operate for just three months, both rovers have now been in operation for six and half Earth years, studying the role of water in the Martian environment.
Opportunity remains in relatively good health, still mobile and able to collect scientific data.