LOS ANGELES - NASA's aging but durable Mars rover Opportunity will make what could be a trip of no return into a deep impact crater as it tries to peer further back than ever into the Red Planet's geologic history.
The descent into Victoria Crater received the go-ahead because the potential scientific returns are worth the risk that the solar-powered, six-wheel rover might not be able to climb out, NASA officials and scientists said Thursday.
The vehicle has been roaming Mars for nearly 3 1/2 Earth years. Scientists and engineers want to send it in while it still appears healthy.
"This crater, Victoria, is a window back into the ancient environment of Mars," said Alan Stern, the NASA associate administrator who authorized the move.
"Entering this crater does come with some unknowns," Stern added. "We have analyzed the entry point but we can't be certain about the terrains and the footing down in the crater until we go there. We can't guarantee, although we think we are likely to come back out of the crater."
Opportunity and its twin, Spirit, have been exploring opposite sides of Mars since landing in January 2004, discovering geologic evidence of rocks altered by water from a long-ago wetter period of the now-dusty planet.
Blasted open by a meteor impact, Victoria Crater is a half-mile across and about 200 to 230 feet deep -- far deeper than anything else the rovers have explored.
"Because it's deeper it provides us access to just a much longer span of time," said Steve Squyres, the principal investigator of the Mars Exploration Rover mission from Cornell University in Ithaca, N.Y. He said it's not known just how much time is represented in the crater's layered walls.
Opportunity's first target will be a band of bright material like a bathtub ring about 10 feet below the crater's rim.
"That was the original, pre-impact surface so this bright stuff is the stuff that was in contact with the Martian atmosphere at the time Victoria formed, which may have been billions of years ago," Squyres said.
The initial entry is expected on July 7 or 9. To get into the crater, the rover will have to safely cross a ripple of wind-formed material at the lip of the crater, the kind of feature that has given it trouble before. The team plans to initially drive only far enough to have all six wheels on the slope and then back up to the top, to analyze how it performed.
"We call that a toe dip," said John Callas, the rover project manager at NASA's Jet Propulsion Laboratory in Pasadena.
Since inception, the twin-rover mission has cost more than $900 million, and now costs $20 million to $24 million annually. Planned to last 90 days, the mission is in its fourth extension and another proposal would continue operations to the end of October 2008.
