THE ICE COMETH: The Mars Reconnaissance Orbiter snapped this image of a frost-encrusted Phoenix lander in July, a month before it entered a dormant "safe mode" for precautionary reasons. Image: NASA/JPL/University of Arizona
For the past few months, NASA's Mars Reconnaissance Orbiter (MRO) has been little more than deadweight—a body as massive as a small car, zooming idly in orbit high above the surface of the Red Planet. After the orbiter's computer suffered a series of unplanned reboots, mission engineers decided in August to hold the probe in "safe mode" to buy time to look for the trouble source while the spacecraft remained in the protective state of limited functionality.
The MRO came out of safe mode December 8 and resumed science operations December 16, but the origin of the resets remains unknown, says mission manager Dan Johnston of the NASA Jet Propulsion Laboratory in Pasadena, Calif. "We're still trying to hunt down the root cause of the safing events," Johnston says, referring to the unplanned reboots that occurred in February, June and twice in August. Broadly speaking, the resets were related to power glitches in the spacecraft's command and data-handling subsystem.
During the long layoff, the MRO operators patched over a potentially crippling vulnerability that had been identified in the process of diagnosing the orbiter's unusual behavior. "What we discovered was that in a very, very low probabilistic scenario that could be brought on by this anomaly that we've seen, the spacecraft's flight computer could be put back into a prelaunch mode," Johnston says. "And that would basically cut us off from communications with the spacecraft—it would be back in a mode where it would want to talk to the launch vehicle on the launch pad."
The orbiter's science instruments are back on line and seem to be functioning well, but it is "actually maybe more expected [than not] that this event will happen again," Johnston says. The spacecraft's travails highlight the difficulty of working remotely in the inhospitable environment of deep space. Down below, on the equally forbidding surface of Mars, the MRO's past and present robotic co-workers, Phoenix and Spirit, bear that difficulty out, as well.
The Spirit rover, nearing the six-year mark in its exploration of Mars, has been stuck in a soft patch of soil for the better part of 2009. (Opportunity, a twin rover of the same vintage, soldiers on robustly on the other side of the planet.) Spirit's controllers, who have been conducting experimental maneuvers to try to free the robot since November 17, quickly lost the use of one of the rover's six wheels when it stalled just days into the extraction effort. But another wheel, which had been immobile for more than three years, came unexpectedly to life on December 12. Rover driver Scott Maxwell noted on Twitter that Steve Squyres, a planetary scientist at Cornell University and principal science investigator on the rover mission, "has proposed that there's a law of conservation of working wheels on Spirit."
Meanwhile, the Phoenix lander, which served as a geologic science platform on Mars for several months in 2008 before succumbing, as planned, to the cold and darkness of Martian winter, has stood encrusted with carbon dioxide ice in the northern plains. In early 2010 springtime will be in full swing on Mars's northern hemisphere, where seasons last roughly twice as long as than they do on Earth; Phoenix will have warmed considerably and will again have access to sunlight for its solar panels. Phoenix principal investigator Peter Smith, a professor at the University of Arizona's Lunar and Planetary Laboratory in Tucson, says that sometime in January the team plans to resume listening for a signal from the lander, which could somehow have survived the winter dormant but intact.
Smith says that picking up a signal from Phoenix would be a "big thrill" but emphasizes that hearing from the lander is improbable. None of the systems were engineered to survive a Martian winter, and the lander has been subjected to any number of threats, from the cold to the prolonged lack of power to the mundane possibility that the solar panels have snapped off under the weight of accumulated dry ice. "The likelihood is that something will break," Smith says. At the same time, he says, "Why not listen? You never know."