NASA?s Spirit rover has encountered a problem on Mars that is familiar to most drivers on Earth: it is stuck in dirt and spinning its wheels.
The five wheels that still rotate on the robot have been slipping severely in soft dirt during recent driving attempts, sinking the wheels about halfway into the ground.
The rover team of engineers and scientists has suspended driving Spirit temporarily while studying the ground around the rover and planning simulation tests of driving options with a test rover at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"Spirit is in a very difficult situation," said JPL's John Callas, project manager for Spirit and its twin rover, Opportunity. "We are proceeding methodically and cautiously. It may be weeks before we try moving Spirit again. Meanwhile, we are using Spirit's scientific instruments to learn more about the physical properties of the soil that is giving us trouble."
Both Spirit and Opportunity have been trundling across the Martian surface for more than five years now, far surpassing their original three-month missions. Opportunity is currently on the opposite side of the planet from Spirit, making its way to its next target, Endeavour Crater.
Spirit has been driving counterclockwise from north to south around a low plateau called "Home Plate" for two months. The rover progressed 400 feet (122 meters) on that route before reaching its current position.
Spirit's current sunken situation has raised concerns that the rover's belly pan could now be low enough to contact rocks underneath the chassis, which would make getting out of the predicament even more difficult.
Spirit's right-front wheel stopped working three years ago. Since then the six-wheeled robot has been driving backward to circumvent the problem. Driving with just five powered wheels while dragging or pushing an immobile wheel adds to the challenge of the current situation.
In 2005, rover controllers had to dig Opportunity out of its own quagmire, when all six of its wheels were stuck in a deep sand dune.
On a more positive note, wind has removed some of the dust accumulated on Spirit's solar panels three times in the last month, increasing the rover's capability for generating electricity.
"The improved power situation buys us time," Callas said. "We will use that time to plan the next steps carefully. We know that dust storms could return at any time, although the skies are currently clear."
Behavioral problems that Spirit exhibited in early April ? episodes of amnesia, computer resets and failure to wake for communications sessions ? have not recurred in the past three weeks, though investigations have yet to diagnose the root causes.