The death watch is on for NASA's Phoenix lander, the first spacecraft to sample water on another planet.
Buffeted by dust storms and chilled by temperatures as low as minus-141 degrees Fahrenheit from the impending arrival of the Martian winter, Phoenix is clinging to life, but barely, NASA officials said Friday.
"We knew this was coming," said project manager Barry Goldstein. "It's bittersweet."
Days earlier, Phoenix fell silent, going into safe mode to save battery power. After failing to answer to two wake-up calls from Earth, it flickered back to life long enough Thursday to send a signal to the Mars Odyssey spacecraft orbiting overhead. It then went back to sleep for another 19 hours to recharge its batteries.
The lander, however, failed to awaken from its latest sleep Friday, alerting NASA officials to the possibility that the end could be very near. "It's going down the way we expected," Goldstein said.
He said mission officials would keep watch over the weekend to see if it revived again.
Phoenix, which landed May 25 on the northern Martian plains, has already survived two months longer than its planned three-month mission. But with the sun sinking lower in the northern sky, the solar panels that power the craft's instruments can't draw as much power. A dust storm this week also applied a fine coat of Martian soil to the solar panels, further limiting their ability to produce electricity.
NASA officials said they hoped to keep the lander alive a few more weeks, to squeeze every last bit of science out of it before it descends into a sleep from which there will probably be no waking. To conserve power, ground controllers plan to shut down four heaters that keep the lander's main instruments warm enough to operate.
"If we did nothing, it wouldn't be long before the power needed to operate the spacecraft would exceed the amount of power it generates on a daily basis," Goldstein said.
The first heater to be shut down is connected to the 7-foot-long robotic arm that dug up the first samples of ice analyzed on an alien world. That heater also warmed the thermal and evolved-gas analyzer, or TEGA, which contained eight ovens used to bake and sniff the soil samples dug up by the robotic arm.
The arm and the TEGA instrument make up the heart of the lander's instrument package. They were designed to answer the central question of the $420-million mission: Could Mars be habitable for some types of simple life forms?
