Phoenix is programmed with a "Lazarus mode" that automatically causes it to reboot itself after losing power. Though Phoenix answered the latest call, it went back to sleep for another 19 hours to recharge its battery. Engineers expect the lander to survive several more weeks.
"We knew this was coming. It's bittersweet," said project manager Barry Goldstein of NASA's Jet Propulsion Laboratory.
Phoenix landed in the Martian arctic in May. During its three-month prime mission, the sun stayed above the horizon, allowing the long-armed lander to dig trenches in the soil and collect ice bits for its various instruments to analyze.
NASA extended the mission in hopes of getting the most science out of the spacecraft before it dies.
In recent days, the weather at Phoenix's landing site has worsened. Overnight temperatures plunged to minus 141 degrees, and daytime temperatures reached only minus 50 - the lowest temperatures so far in the mission. The lander also weathered a dust storm.
Phoenix landed in a patch of ice in Mars' high northern latitudes to study whether the environment could be friendly to microbial life. It has found evidence that the ice may have melted at some point, although the soil is dry. It has yet to find the presence of organic, or carbon-based, compounds that are considered essential for life.
