The Mars Rover called Opportunity is poised to reach another milestone. In a week or so, the rolling robotic geologist will arrive at a large impact crater called Victoria. When opportunity landed in January 2003, even the most cockeyed optimist wouldn't have predicted it would make it to a crater four miles away. Well, now it has. And as NPR's Joe Palca reports, scientists anticipate the crater will provide fresh insights to the red planet's past.

JOE PALCA: Mars is a very dry place today, but scientists think it was once much wetter. NASA sent the rovers to Mars to find evidence of those wetter days. NASA's Matt Golombek is one of the lead rover scientists. He says, on its trek to Victoria Crater, the rover has found patterns on rock surfaces and sulfur-rich mineral deposits that must have been made by water.

Mr. MATT GOLOMBEK (Rover Scientist, NASA): Now, the chemistry of the water was pretty acid-rich, and probably not what you would call very wonderful for life.

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Mr. GOLOMBEK: But it's no question it was wet.

PALCA: Golombek thinks where opportunity is driving today, there might have once have been a shallow lake, and the walls of Victoria Crater may convince any skeptics. That's because images of Victoria Crater from orbiting satellites show what appears to be a wall of rock that's been around for billions of years.

Mr. GOLOMBEK: We don't know what it's going to look like from the ground level. We have high-resolution images from orbit, but that's a very different perspective than when you're on the ground.

PALCA: By examining the different layers of rock, Golombek says scientists can get a better idea of whether surface water was there, and if so, for how long. Golombek says it will take a while for Opportunity to learn it can from the crater walls.

Mr. GOLOMBEK: It could take a year to explore Victoria. Hopefully, our rover will cooperate with us.

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PALCA: So far, the rover has been cooperating admirably. Opportunity's 90-day mission is about to enter its fourth year, and Golombek says the rover is showing few signs of slowing down.

Joe Palca, NPR News, Washington.

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SIEGEL: You can see photos of the Mars rovers Opportunity and Spirit at work. They're at

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SIEGEL: Understanding crime statistics. That story next on ALL THINGS CONSIDERED.

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