PASADENA, California (AP) _ NASA's Mars rover Opportunity will be sent into a big crater that could offer clues to the planet's history of water, despite the risk that the craft may not be able to get out, the space agency said.

The potential scientific value of exploring Endurance Crater outweighs the risk that the six-wheeled rover may not be able to drive back up its inner slope, mission officials said Friday.

The decision was made after extensive study of the impact crater as the rover moved along its rim.

Scientists are intrigued with bedrock in the crater that is older than a similar outcrop a half-mile (about 1 kilometer) away that Opportunity previously determined formed in a once-wet environment suitable for life.

The earliest Opportunity could be sent into the 140-yard(meter)-diameter crater would be early next week, NASA said.

Richard Cook, rover project manager at JPL, said one of the exposed rock layers will require driving only 16-23 feet (5-7 meters) down into the crater on a 25-degree slope.

"We'll take an incremental approach, edging our way down to the target," Cook said.

Opportunity will use its instruments to study the rock layers for several days, and then will be ordered to reverse back up the slope and exit the crater.

Opportunity and its twin, Spirit, have been working on opposite sides of Mars since landing in January.