has made it to the lip of Victoria Crater, a fairly large crater on Mars, said Steve Squyres, the principal investigator from the Mars Exploration Rover program and a professor at Cornell University. Victoria's geology potentially will yield important clues about the chemistry and extent of the groundwater that Squyres and others believe existed on Mars in the distant past.
Getting to Victoria has taken about 21 months and required Opportunity to drive about 7 kilometers, often over bumpy terrain. Now that it's at Victoria, Opportunity will visit various promontories while scientists try to figure out a route for it to enter and exit the crater.
The debate about whether Mars ever had water is more or less over, he noted. Minerals dug up by the rovers indicate that water existed on the planet in the distant past. Scientists are now trying to determine things like what the pH balance of that water was and other issues.
Most of the water, however, was locked underground. The rover project so far has found only three small sites that indicate water pooled on the planet's surface.
"There was an awful lot of groundwater here, but only rarely, separated by space and time, did it come to the surface," he said during a presentation at theconference taking place this week in San Francisco. "Mostly, it was an arid environment."
Still, Mars, or at least its atmosphere, isn't completely dry now either. Ray Arvidson, the deputy principal investigator on the project and a professor at Washington University, noted that Spirit, the other Mars rover, found evidence of ice clouds in the last nine months.
"We've seen water-ice clouds, which we didn't see last year," he said.
The Mars Rover program has exceeded all expectations. Originally, scientists expected the rovers to run for only 90 days. The two vehicles are close to approaching their third anniversaries.
See the latest NASA flight report for the Mars rover project.
One of the major factors in the longevity is the Martian wind. The vehicles run on solar power, and scientists anticipated that dust would cake over the solar panel in about three months, bringing the vehicles to a halt. Instead, wind has swept them clean, something they didn't anticipate. The mission has gone on so long that researchers have had to patch the software on the vehicles so that it can tabulate days in the thousands. Initially, the counter stopped in the three digit range: the problem was analogous to the Y2K problem.
To keep going, the scientists park the vehicles on slopes to recharge. Right now, Opportunity is more mobile than Spirit. The right front wheel of Spirit got stuck about nine months ago. As a result, Spirit has stayed in a small, circumscribed area and has to be driven backward, said Arvidson.
Someday, both vehicles will grind to a halt. Every year, the scientists involved in the project put $20 into a pool and bet on how many will be left a year from now, Squyres said. So far, he's lost every time.