Mars rover spies crater's edge

Scientists say the edge of Bonneville lies on the horizon

The US space agency's robotic Mars explorer Spirit can now see the edge of a large crater it has been travelling to for several days.

Spirit is making the trek from its landing site to a 150m-wide crater named Bonneville, where it will carry out a scientific investigation.

Scientists do not know if Spirit will be able to roll into the crater or if its slopes will be too steep.

A power drain still threatens the lifespan of its "twin" Opportunity.

Bonneville, located in the flat basin of Gusev Crater, is thought to be about 15m deep. Scientists have tried to obtain elevation models for the crater, but they cannot yet determine the slope.

"[I don't know] what the feasibility is in terms of hazard avoidance of getting the rover down into the crater," said deputy principal investigator Dr Ray Arvidson.

"Or for that matter, since we haven't imaged the interior with Pancam (panoramic camera) or Mini-Tes (Mini-Thermal Emission Spectrometer), whether it's worth it."

If mission scientists decide that negotiating the sides of the crater will be too risky, or if the site does not interest them, the rover will turn to the south-east and head off to investigate a series of hills.

Definitive answers

Dr Arvidson said he was confident the missions would come up with definitive answers about the geological forces that shaped the sites being explored by the rovers.

"I'm pretty sure that we're getting the data we need to answer those questions," he said.

"If we conclude that water was involved in the surface or sub-surface at some time, the probability that pre-biotic systems could have been generated and life could have started goes way up."

"It's going to take a couple more sols to come up with the measurements to answer these definitive statements."

The power drain that continues to trouble Opportunity is caused by a thermostatically-controlled heater in the shoulder joint of the rover's arm, which turns on automatically in response to drops in temperature.

Mission manager Jennifer Trosper said that when the mission started about 10% of Opportunity's energy was being drained by the heater.

As the mission progresses, Opportunity gets less Sun on its solar arrays and the energy lost from the rover rises to 20%.

But Ms Trosper said scientists were devising a software patch for the rover that would allow them to turn the heater off.

"[We will] be giving ourselves the ability to turn that heater off completely, so it won't be a drain on the batteries overnight," she told journalists.