No one has heard from Phoenix for more than a year, ever since NASA's polar lander succumbed to the circuit-shattering cold of the approaching Martian winter. Yet the mission's scientists and engineers are still keeping an eye on their charge, and new views released this week show the lander partially mantled in dry-ice snow.
Last July and again in August, the HiRISE camera aboard Mars Reconnaissance Orbiter returned its gaze to the bleak plain called Scandia Colles, at a latitude of 68° north, where Phoenix touched down on May 25, 2008. The orbital views show the lander in dim light as northern winter neared its end. The view here gives the impression of frosty patches atop ice-free ground, but that's an artifact of contrast enhancement. In fact, the entire scene is covered with frozen carbon dioxide.
We'll probably never know how just how much CO2 snow accumulated atop the lander by September, when the coating was likely thickest, because the orbiter has had problems of its own. After four self-induced shutdowns earlier this year, MRO remains in electronic hibernation while ground controllers try to cure its problems. That means HiRISE has been unavailable to monitor conditions at Phoenix's landing site as sunlight returns and the blanket of dry ice slowly vaporizes.
Thomas Prettyman (Planetary Science Institute) estimates that, at its peak, the pile of CO2 in the lander's vicinity would total about 30 grams per square centimeter. That's enough to make a dense slab of dry ice at least 7½ inches (19 cm) deep, or a much thicker layer if it were the fluffy stuff. "This would be similar to having a foot of solid water ice on top of your car here on Earth," Prettyman explains. "It's probably not a good idea to leave your lander out in the snow."
With temps having plunged plunged to -240°F (-150°C), engineers give the unheated Phoenix little chance to survive. The craft's fragile solar-cell arrays, not designed to support much weight, have likely cracked and fallen off from the weight of all that dry ice.
Still, the team will try to reestablish contact in about a month, when the seasonal situation will be much like that when Phoenix landed. Ground stations will send a wake-up call to the spacecraft as the Mars Odyssey orbiter is overhead and listening for a response. "The solar-cell panels must revive the battery and bring the computer system up to working order," explains project scientist Peter Smith (University of Arizona). The communication system must also revive, and the lander must be awake while Odyssey is overhead.
"It's a lot to expect," Smith admits, "but we will try."