Images from the High Resolution Imaging Science Experiment (HiRISE) camera on board the Mars Reconnaissance Orbiter, taken during the first few weeks of the Martian spring, had detected a change in the size of the orbiter, evidenced by the shadows the lander casts.
The shadows show a smaller lander, possibly caused by the accumulation of ice over the winter months, which could weigh hundreds of pounds, according to Michael Mellon of the University of Colorado at Boulder, a science team member for Phoenix and HiRISE. This ice has the potential to bury the lander's solar panels or even break them, rendering them unable to supply power to the lander.
Jet Propulsion Laboratory scientists say the lander was not designed to survive the cold and icy winter.
As spring arrived on Mars this year — seasons are twice as long on Mars as they are on Earth — NASA decided to try to contact the lander again to determine whether it had indeed expired.
"It would be unfortunate if NASA had not tried to contact it and what we had was a working spacecraft," Bass said.
Phoenix is responsible for some major breakthroughs in Earth's exploration of the Red Planet, including confirming the existence of underground water ice, a discovery made by NASA's Mars Odyssey orbiter.
Phoenix also detected the basic components in the Martian soil necessary to harbor life. The lander also detected signs of perchlorate, an oxidizing chemical, in the soil above a thin layer of ice that on Earth could be used as food for some microbes, but could be toxic to others.
"It sucks the water out of the atmosphere and acts as an energy source for some forms of life, and it destroys other forms of life," Bass said.
The science gathered from the mission will be used for many years in the future, said Fuk Li, manager of the Mars Exploration Program at JPL.