US Mars Rover Misses Best Sites

America's Spirit rover has landed in an arid enclave of Mars that is tantalisingly out of reach of the region's most promising sediments and rocks, dismayed scientists have discovered.

As a result, Nasa's engineers may be forced to try to make their trolley-sized robot craft travel much further than it was designed to do to reach soil that could contain evidence of water or even life.

Spirit landed two weeks ago in Gusev Crater, which is thought to have held a lake in Mars's ancient past. But initial surveys show that the 95-mile-wide depression appears to have been blanketed by volcanic debris and scoured by the wind.

The deposits of lake sediments that scientists had hoped to find have either been buried or erased by billion years of vigorous geologic activity. 'Goodness knows what might have been stripped away,' said Mars scientist Maria Zuber, of the Massachusetts Institute of Technology.

The discovery means that Spirit might have to roam farther than Nasa expected to find the evidence scientists seek. The most promising place appears to be a group of hills that scientists can see from photographs sent back by the rover.

These hills, a few hundred feet high, represent a far bigger slice of the planet's history than Spirit's current position. Although its solar-power 100-watt engine will run for three months, the craft can only trundle a few yards a day. Engineers are now calculating how much ground it will need to cover to reach those slopes which could contain carbonate rocks, such as limestone, that form in water.

If Spirit cannot travel that far, they may have to settle for investigating a nearby crater.

A second craft, Opportunity, is on track to land next Sunday at a site half way around the planet from Spirit. Its landing site abounds in a mineral called grey hematite, which is associated with liquid water.