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It has been driving on and off for more than seven years, but this month it reached its new destination. Opportunity, a small exploratory rover that landed on Mars in 2004, has trundled to a crater called Endeavour.

And the first rock it looked at has already opened a new chapter in the study of Mars, NASA scientists said Thursday. During a telephone news conference, mission scientists giddily described that rock: full of zinc and bromine, elements that, at least for rocks on Earth, would be suggestive of geology formed with heat and water.

“This rock doesn’t look like anything else we’ve seen before” on Mars, said Steven W. Squyres, a professor of astronomy at Cornell and principal investigator of the rover mission.

The rim of Endeavour — a 14-mile-wide depression that was carved out by an impact long ago — consists of rocks from an earlier geological era that the impact lifted up from below. If the aging rover holds up, it could spend years examining the new terrain, giving NASA scientists ample grist for discovery.

Scientists are most interested in a close-up look at clay deposits that have been detected from orbit by another craft — NASA’s Mars Reconnaissance Orbiter — but that Opportunity has yet to find. Clay forms in the presence of liquid water, and the deposits suggest a warmer, wetter period in Mars’ past that may have offered friendlier conditions for life.

“This is a brand new mission, brand new landing site for all intents and purposes, geologically,” Squyres said. “A whole new set of puzzles for us to go off and solve.”

Opportunity and a twin rover, Spirit, arrived on Mars in January 2004, landing on different sides of the planet with the goal of exploring the surface for signs of past water. Spirit got its wheels stuck in a sand trap in May 2009 and could not get its solar panels pointed toward the sun; unable to generate enough electricity, it stopped communicating in March 2010 and is not expected to be heard from again.

But Opportunity, about the size of a golf cart, continues rolling on. It has now driven 20 miles. It had been designed to travel about two-thirds of a mile. When it landed in 2004, it rolled by chance into Eagle Crater, which is 70 feet in diameter, and over the years explored a series of progressively larger craters. Three years ago, Opportunity — which had already far outlived its original mission — set off on a journey that no one was confident it would complete. It drove 13 miles to Endeavour, arriving on Aug. 9.

Opportunity is now usually driven backward to even out the wear on the gears. One of the joints on the robotic arm is stuck.

Both rovers have discovered evidence of liquid water, albeit water that is highly acidic, like sulfuric acid, that made parts of ancient Mars potentially habitable, at least intermittently.