Cautious mission managers had put tight constraints on the Spirit’s movement to ensure that it did not drive itself into a deeper predicament. Because the uncertainty in its tilt was more than one degree, the rover called it a day. Spirit awaits new instructions.
The engineers are “still analyzing that result before they decide what to do with the next drive,” said Guy Webster, a spokesman at the Jet Propulsion Laboratory in Pasadena, Calif., which operates the Spirit and another rover, Opportunity.
The commands to the rover were for it to make two forward motions, rotating its wheels three revolutions each time. If the rover were on solid ground, that would have carried it about five yards.
Officials at the National Aeronautics and Space Administration have said they will give the rover managers until at least February to try to pull the Spirit out of the sand trap.
At least the rover has been stuck in an interesting place.
One side sits on basaltic sand mixed with iron oxide dust, typical for most of Mars. The other side is sunk in sands rich in minerals known as sulfates, which tell of an era long ago when acidic waters flowed in this region.
“This turns out to be a geologic treasure trove,” said Raymond E. Arvidson, a professor of earth and planetary sciences at Washington University at St. Louis and the mission’s deputy principal investigator.
The sands are richer in sulfates than anywhere else measured so far by the Spirit or the Opportunity, which is on the other side of the planet.
“What’s really interesting,” Dr. Arvidson said, “is the material is layered.”
The layers vary in appearance and composition, perhaps a result of climatic changes in the geologically recent past.
Mars’s axis periodically tips over, leading to colder temperatures and snowfall near the equator. Sunlight shining through the ice and snow could have heated the ground and melted ice, and the water then dissolved and washed away some of the sulfates, producing the layers. The grains in the top few sulfate layers were cemented together.
The Spirit drilled two small holes into the surface. In one hole, the drill broke through to sulfate sands. In the other hole, about four inches away, there were no signs of sulfates at all.
“We are sitting astride a geologic boundary,” Dr. Arvidson said. “It goes right down the middle of the rover.”
A rock may be touching the bottom of the rover, which could further complicate the possibility of escape. Also, the rover is tilted toward the side, toward the interior of the crater, and one of the six wheels malfunctioned several years ago and no longer turns.
In six months of testing, said John Callas, the project manager, “we have not been able to demonstrate a path to extrication.”
Dr. Callas remains hopeful, though, because Mars is considerably different from Earth, with about one-third the gravity and almost no moisture in the atmosphere.
Yet even if the rover never gets out, its scientific value could continue as a weather and seismic monitoring station. The rover has outlived its original three-month mission by more than five and a half years.
The Opportunity, meanwhile, continues to make steady progress toward a giant crater where scientists hope to explore geologic layers farther into Mars’s past. That destination is still about six miles away, or at least another year of traveling. ( nytimes.com )
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