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After an arduous 21-month journey, the Mars rover Opportunity edged close enough to the rim of a large crater Wednesday to send back its first photos of the bottom and rocky sides of the dramatic site.

What they showed left researchers increasingly confident that their robotic explorer had reached a scientific gold mine that will dramatically increase their understanding of the planet’s history.

NASA scientists said the rover came within about 15 feet of Victoria Crater’s rim and was scheduled to climb over a small sand dune Wednesday night and stop right at the crater’s edge.

“The pictures we got tell us there is a tremendous amount of geologic information hidden in that crater,” Steven Squyres of Cornell University, principal science investigator for the mission, said Wednesday. “What secrets it actually holds we won’t know till we begin to get the data. But yesterday’s picture alone makes the voyage worthwhile.”

Opportunity, which has survived on Mars 10 times longer than initially was thought possible, traveled more than 6 miles to get to Victoria – a pit created by an impact that is 200 feet deep and half a mile across. It is substantially larger than any crater explored so far by the twin Martian rovers, Opportunity and Spirit.

National Aeronautics and Space Administration scientists were ecstatic about the day’s progress and images and said more is to come. The Opportunity team is scheduled to meet today to decide which of two rock promontories, dubbed Cape Verde and Cabo Frio, would give the rover the best view of Victoria. The outcroppings project into the crater, and scientists said they would allow the rover to take dramatic panoramic shots in color with its high-resolution camera.

Bruce Banerdt, a NASA project scientist, said Wednesday’s images showed some of the rock stratification that geologists associate with earlier presence of liquid water.

He said Martian geology appears to be similar to Earth’s, although the long absence of water allows rocks to remain unchanged for much longer periods.

“We’re seeing similar features (at Victoria Crater) as what we’d see on Earth,” he said. “But instead of being tens of millions of years old, these Martian rocks are billions of years old.”