The Opportunity rover is on track to roll onto Mars (search) as early as Sunday, just days before its twin could resume its own work exploring the Red Planet, NASA said Wednesday.

Opportunity unfolded its front wheels and locked them into position, leaving just a few more tasks before being ready to travel the final 10 feet from its lander and onto the surface of Mars, mission members said during a news conference at the Jet Propulsion Laboratory (search).

The National Aeronautics and Space Administration (search) still wants to adjust the forward tilt of Opportunity's lander, pitching it down 5 degrees to smooth the six-wheeled robot's path. Engineers hoped to complete that work in time for a late Sunday roll-off, rover activity lead scientist Rick Welch said.

Meanwhile, engineers worked to regain full control of Spirit, which has been sidelined for a week on the other side of the planet with crippling software problems.

"We are working to get complete control of the vehicle but still aren't quite there yet," said Jennifer Trosper, a mission manager.

Spirit began using its high-gain antenna again late Wednesday, which should speed the transmission of data needed to debug the rover's computer system.

Spirit also took its first picture in more than a week, mission manager Mark Adler said. The picture shows Spirit's arm, poised as it had been in front of a rock scientists have dubbed Adirondack.

"Everything's right where we left it," Adler said.

To fix Spirit, engineers planned to selectively pluck files from Spirit's overloaded flash memory or, if that fails, simply wipe it clean.

Depending on the outcome, Spirit could return to its science work early next week, Trosper said. It could resume taking engineering pictures before then.

NASA sent Spirit and Opportunity on the $820 million mission to Mars to probe for geologic evidence of the past presence of water on what is now a largely dry, dusty planet.

That evidence could be a short drive from where the six-wheeled Opportunity now sits, in horizontally striped and fractured slabs of bedrock.

On Wednesday, NASA released the first color photographs taken by Opportunity of fine layering in a rock outcropping roughly 10 yards from the rover. New black-and-white images show the formation in even higher resolution.

"Some of the detail you can see in here is pretty phenomenal," said camera scientist Jim Bell.

Scientists said patches visible in the layers appear to contain pebbles and other small stones that could indicate the rock formed in water. Drifting volcanic ash or wind-borne sediments also could have built up the thin layers.

The outcropping rims a portion of the small crater in which Opportunity landed.

"Landing inside a crater turned out to be a blessing," landing site scientist Matt Golombek said.

Opportunity was in good shape after its weekend landing but had developed a small, 15-watt power loss that worried NASA. Engineers believe a heater in the shoulder of its robotic arm has been turning on unnecessarily when temperatures drop. Typically, the heater is needed only when the arm is in use, mission manager Jim Erickson said.

Engineers were unsure whether the situation could harm the rover, which uses solar panels that produce up to 900 watts of power.