NASA/JPL

A view of Mars' Victoria crater as seen by Opportunity's navigation cameras. The rover reached Victoria after a 21-month drive. The crater's layered rocks could offer a wealth of new information about Martian history.

NASA's Mars rover Opportunity has rolled up to the rim of Victoria crater after a 21-month trek across the vast expanse known as Meridiani Planum. And 250 million miles away on Earth, the view -- according to astronomer, geologist and mission principal investigator Steve Squyres -- is "just breathtaking ... the most spectacular thing we've seen."

From the rover's perch, the crater offers a visual timeline of Martian history in the layers upon layers of exposed rock.

"This is the absolutely highest-priority destination we could have reached," said Squyres. "Those layers of rock, if we can get to them, will tell us new stories about the environmental conditions long ago. We especially want to learn whether the wet era that we found recorded in the rocks closer to the landing site extended farther back in time. The way to find that out is to go deeper, and Victoria may let us do that."

Victoria crater is about 800 meters (half a mile) across -- that's about five times wider than Endurance crater, where Opportunity spent six months in 2004, and about 40 times wider than Eagle crater, where Opportunity landed in January 2004.

It's too soon to tell whether there are any smooth routes down into the crater (which is estimated to be about 200 feet deep), said Squyres. But the initial signs look encouraging. And as for what they will find -- he's keeping an open mind. "We're going to go down [into the crater] to see what Mars has to tell us," he says.

Opportunity's exploration of Mars has lasted more than 10 times longer than the originally planned three-month mission. The rover has driven more than 9.2 kilometers (5.7 miles), much of that across the wide, flat plain between Endurance crater and Victoria. On the other side of Mars, Opportunity's twin, Spirit, is hunkered down in the Gusev crater conserving energy through the Martian winter.

Mars will pass behind the sun through most of October, limiting communication between the rovers and Earth. That period (called conjunction) will begin in about three weeks, and the rovers must be situated and prepared within the next week. "We're working as fast as we can," says Squyres. During conjunction the rovers will remain stationary and operations will be reduced.

The Jet Propulsion Lab, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for NASA.