"This is not like getting your car stuck in the mud," he said. When last commanded to move, "the rover made a tiny bit of progress, which we intend to exploit to get the rover out."
The primary goal of the Earth-based testing is to make sure the situation doesn't get worse and leave Spirit irrevocably trapped.
But even if the worst happens and Spirit is entombed where it sits, that won't be the end of its mission, Callas said. Instead of a rover, it would become a stationary lander of the sort NASA has sent to Mars repeatedly over the years. It could still do science from its new, permanent home.
Getting embedded has already yielded some surprising science, Callas said. By digging so deeply into the soil in one spot, the rover has turned up evidence of ferric sulfate, calcium sulfate and silica, which Callas said could be evidence that snow or ice was present at the equatorial regions of Mars in the fairly recent past. These days, water ice on the Martian surface is believed to be located only at the poles. This discovery is more proof that, where the rovers are concerned, "when Mars hands us lemons, we make lemonade," Callas said.
While Spirit is parked, Opportunity, on the other side of the planet, is continuing to head for a crater called Endeavour. The twin rovers have far exceeded their expected lifetimes, and Callas declined to speculate how much longer they could last.
"These are phenomenal vehicles," he said. "They go through horrendous thermal cycles, about 150 degrees Fahrenheit each day. That's very stressing on a vehicle."
Though freeing Spirit is a challenge, Callas said this event is not yet the worst threat to the survival of the rovers. The greatest danger comes from periodic global dust storms that can blot out the sun, robbing the rovers' solar panels of power. In November, a storm that hit the area where Spirit was exploring was so severe that JPL managers called workers in on the weekend to send commands to the rover to save energy.
"It was like having a child lost in the wilderness," Callas said. "On that one, I was losing sleep."
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john.johnson@latimes.com
