Mars Rover Stopped in Its Tracks

Dick writes about Earth and planetary science for Science magazine.

The Spirit rover has bogged down on Mars, a development that could end its long-running mission of exploration. NASA announced late yesterday that Spirit had dug its wheels deep into the fluffy remains of an ancient volcanic steam vent. Ironically, such salty, flour-like deposits are among Spirit’s greatest discoveries in its 5 years of roaming Gusev Crater.

Both Spirit and its sister machine—Opportunity, on the other side of the planet—have encountered some tough roving before, but this time Spirit seems to be in a real pickle. The soft soil entrapping Spirit “is very insidious stuff,” says Mars rover principal investigator Steven Squyres of Cornell University. “You cannot detect it without stumbling into it.”

Spirit rover Getting Spirit out is going to be “tough with a 5-wheel rover,” says Squyres. Spirit has been dragging one dead wheel in the dirt for 3 years now, but it’s worse than that, according to rover project manager John Callas of the Jet Propulsion Laboratory in Pasadena, California. Spirit’s wheels are practically buried in the soft soil (see the two tracks in this image), its left-middle wheel has stalled, and “the rover’s belly may be sitting on a small mound of rocks.” That would tend to take the rover’s weight off the wheels, which need the weight to get traction. “Spirit is in a very difficult situation,” Callas concludes.

Spirit may yet escape, but its predicament raises the specter of shutting down a still-capable vehicle. “We really have not developed a ‘do not resuscitate’ list” of circumstances mandating ending a mission, says Mars exploration lead scientist Michael Meyer of NASA headquarters in Washington, D.C. If Spirit cannot be moved, for example, all concerned would review the spacecraft's health, the science that could be done from an immobilized rover, and the cost of that science. Currently, the two rovers cost $20 million per year to operate. Would images of winter setting in on Mars 6 months from now be worth $27,000 a day? NASA may have to decide.

Photo: NASA

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