The crater is 150 meters (492 feet) long and about 15 meters (49 feet) deep and offers a window into Mars' geology, said Ray Arvidson, assistant chief of scientists at the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena, California.

Spirit will take its most difficult trip since landing on Mars in January by traveling 80 meters (262 feet) through uneven terrain, more than a week after beating the 1997 Sojourner robot's distance record.

"In about two weeks, Spirit will be at the crater," Arvidson said. "And that's going to be a different phase of the mission, looking at the bedrock and the floor of the crater."

The rover will make several stops during the trip to use analysis tools and use its drill to pierce through rocks.

NASA's second rover, Opportunity, which landed on the opposite side of Mars, drilled a rock in an area named El Capitan.

The rover photographed and probed the rock. Results of the analysis are expected in a few days.

"Both (rovers) are doing fantastic from a health point of view," said Jennifer Trosper, Spirit mission manager.

NASA is planning to replace part of the rovers' software with new programs in a month, allowing them to continue their missions as the energy generated by their solar panels drops, Trosper said.

SPACE.WIRE