"We have confirmed that Spirit is booting up normally," said Mark Adler, mission manager at NASA's Jet Propulsion Laboratory in Pasadena, California.

NASA engineers fixed Spirit by erasing several thousand files clogging its computer's flash memory. These non-essential files accumulated during the rover's seven-month trek through space.

The excess files caused Spirit's computer to reboot unexpectedly, preventing the golf-cart-sized robot from working properly.

"Tomorrow we'll be doing some preventive maintenance," Adler said on Sunday. "To be safe, we want to reformat the flash (memory) and start again with a clean slate."

Spirit will continue this week examining a rock that has been dubbed Adirondack.

Opportunity lands

On the other side of the planet, the rover Opportunity, which landed three weeks after Spirit on 24 January, successfully rolled out of its landing platform.

The Opportunity rover cutting
away from the lander (top)

The probe transmitted a black-and-white image of its base station after rolling onto the Martian surface at 1100 GMT, nearly a week after landing on the planet, indicating its journey had been a success.

The six-wheeled vehicle's tracks could clearly be seen in the image.

Controllers, optimistic about the mission's success, had decided to move the probe 24 hours earlier than planned.

"We're ahead of schedule and taking advantage of the fact that Opportunity treats us well," Daniel Limonadi, rover systems engineer at NASA, said.

Opportunity is scheduled to extend its instruments through Monday and begin examining Mars' soil, said Matt Wallace, one of the mission's managers.

Opportunity is inside a small crater in an area known as the Meridiani Planum, believed to be the flattest place on Mars. Spirit is on the Gusev crater.

The goal of the $820 million mission is to determine whether there is evidence that Mars once had the environmental conditions to host life.