The lander’s batteries appeared to have drained, mission managers said, with all systems, including its heaters, shut down. The mission managers had instructed the spacecraft to wake up and send word of its condition at 12:30 a.m. Thursday via the Mars Reconnaissance Orbiter, which was passing overhead. It did not.
But the spacecraft is programmed with a so-called Lazarus mode that enables it to resuscitate itself and recharge its batteries during the day.
Once restarted, the lander conserved its energy for 17 hours, then tried to communicate for two hours with any orbiter passing overhead, repeating the cycle until it received new instructions.
The lander successfully communicated with the Mars Odyssey orbiter Thursday evening.
A NASA statement said: “The communication reinforced a diagnosis that the spacecraft is in a precautionary mode triggered by low energy. Mission engineers are assessing the lander’s condition and steps necessary for returning to science operations.”
The Phoenix landed in May, during spring in the Martian northern polar region, to study a vast expanse of ice just below the surface. It has found signs that the ice may have melted in the past — the presence of carbonates, which form in the presence of liquid water — but its measurements also show current conditions to be very dry.
The lander’s last experiment, using a small oven to cook a sample of soil, was completed over the weekend. Data from the experiment was sent back before the shutdown and could answer whether the Martian soil contains organic compounds.
The Phoenix’s mission was scheduled to last three months but was extended to allow scientists to squeeze every bit of data from the spacecraft.
Now, with the dwindling sunlight of the Martian winter, the lander’s solar panels will produce less energy.
A dust storm on Monday further reduced the amount of power the panels could produce. Coupled with the energy drain from the last experiment and surface temperatures as low as minus-141 degrees Fahrenheit at night, the spacecraft put itself into its safe mode on Tuesday, shutting down nonessential activities.
The lander also shut down one of its two batteries and switched to backup electronics systems, and some energy-saving commands sent to the primary electronics were not performed.
Even though the lander revived, its demise is probably less than a month away. Peter H. Smith of the University of Arizona, the mission’s principal investigator, said it would be nice to watch winter develop through the lander’s instruments. “But that’s gravy,” Mr. Smith said. “We got what we came for.”