BOULDER, Colorado—It has been a long, hard drive on Mars for NASA's Opportunity rover.

Wheeling across the open, parking lot-like dune fields of Meridiani Planum, the robot is nearing a major milestone: rolling up to "Victoria", a crater that is roughly half a mile (750 meters) wide and 230 feet (70 meters) deep.

From where Opportunity now sits, Victoria is just a short spurt away at 360 feet (110 meters). [Map]

But before pulling up to the large crater, the robot is inspecting a smaller feature named Emma Dean, said Steve Squyres, science team leader of the Mars Exploration Rover mission and a space scientist at Cornell University in Ithaca, New York.

"Emma Dean should be our last stop before we reach the rim of Victoria crater," Squyres told SPACE.com. "It's an important target, because it may excavate into material that was ejected from Victoria crater. As such, it may offer one of the best near-term chances we'll have to sample such material. Once we're done with Emma Dean, we're going to sprint for the rim of Victoria."

[...]

John Callas, JPL rover project manager, saluted the long list of accomplishments that both Spirit and Opportunity have chalked up since their respective touchdowns in January 2003.

Each robot is showing some signs of aging, Callas explained. For instance, a joint in Opportunity's robot arm stalled last week as it was trying to start measurements on a trench it dug.

"We can't say how long the rovers will last," he said, "but we will push to get the best possible science out of these national treasures as long as they keep operating. Victoria could very well be the most productive and exciting science of the entire mission."...