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Harsh weather forced the UA-led Phoenix Mars lander to shut down on Tuesday night in what officials said could mark the beginning of the end of the spacecraft's mission.

After mission officials announced a plan to begin conserving Phoenix's dwindling power supply on Tuesday, they received word from the lander that it had shut down because of a power failure, a Wednesday news release from NASA's Jet Propulsion Laboratory said.

Known as safe mode, the backup procedure stops all non-critical operations while Phoenix awaits instructions from mission planners on Earth. The lander won't conduct any further experiments or scientific work for several days while the spacecraft tries to recharge its batteries.

For the past month, Phoenix has been losing solar power as the daylight increasingly gives way to the darkness and harsh weather of winter on Mars' northern arctic plains.

Phoenix's inability to draw in solar energy as it did during the first 90 days of its summer mission comes at the worst possible time, as temperatures as low as 141 degrees below zero have gripped the region and forced the spacecraft to become more reliant on its heaters.

The cold triggered the lander to turn on heaters for its batteries for the first time Tuesday, which officials partially blame for the power failure.

The primary cause of the failure likely was a dust storm and clouds above Phoenix that kept the spacecraft from drawing in much-needed solar power, the news release said.

The latest development has mission planners wondering how much longer Phoenix might survive.

"This is a precarious time for Phoenix," Barry Goldstein, Phoenix's project manager for the JPL, said in the release. "We're in the bonus round of the extended mission, and we're aware that the end could come at any time.

"The engineering team is doing all it can to keep the spacecraft alive and collecting science, but at this point survivability depends on some factors out of our control, such as the weather and temperatures on Mars."

Peter Smith, the UA's lead scientist on the mission, was traveling back from JPL headquarters in California on Wednesday night and was unavailable for comment.

Mission officials long have predicted the end of Phoenix once the harsh Martian winter set in and have been elated that the mission has lasted two months longer than they had originally expected.

If Phoenix is able to bounce back from the power failure, it's not clear what the lander will be able to do, as engineers already have shut down heaters that warm the robotic arm and the oven-like science instrument known as the Thermal and Evolved Gas Analyzer.

It won't be long before Phoenix reaches a state in which it requires more energy to stay alive than it can take in through its solar arrays.

"It could be a matter of days or weeks before the daily power generated by Phoenix is less than needed to operate the spacecraft," JPL mission manager Chris Lewicki said in the press release. "We have only a few options left to reduce the energy usage."

The lander first touched down on Mars during Memorial Day weekend, after traveling more than 420 million miles.

The University of Arizona led Phoenix's day-to-day research out of a facility in Tucson and became the first public university to lead a NASA mission to Mars.