Opportunity is now driving to a new study area after a dramatic finish to 20 months on "Cape York."
The fractured rock, called "Esperance," provides evidence about a wet ancient environment possibly favourable for life, mission's principal investigator, Steve Squyres of Cornell University, Ithaca, NY, said.
"Esperance was so important, we committed several weeks to getting this one measurement of it, even though we knew the clock was ticking," said Squyres.
The mission's engineers at NASA's Jet Propulsion Laboratory, Pasadena, had set this week as a deadline for starting a drive toward "Solander Point," where the team plans to keep Opportunity working during its next Martian winter.
"What's so special about Esperance is that there was enough water not only for reactions that produced clay minerals, but also enough to flush out ions set loose by those reactions, so that Opportunity can clearly see the alteration," said Scott McLennan of the State University of New York, Stony Brook.
This rock's composition is unlike any other Opportunity has investigated during nine years on Mars - higher in aluminium and silica, lower in calcium and iron.
The next destination, Solander Point, and the area Opportunity is leaving, Cape York, both are segments of the rim of Endeavour Crater, which spans 22 kilometres across.
The planned driving route to Solander Point is about 2.2 kilometres. Cape York has been Opportunity's home since the rover arrived at the western edge of Endeavour in mid-2011 after a two-year trek from a smaller crater.
The first drive away from Esperance covered 24.9 meters.
Three days earlier, Opportunity finished exposing a patch of the rock's interior with the rock abrasion tool.
The team identified Esperance while exploring a portion of Cape York where the Compact Reconnaissance Spectrometer for Mars (CRISM) on NASA's Mars Reconnaissance Orbiter had detected a clay mineral. Clays typically form in wet environments that are not harshly acidic.
For years, Opportunity had been finding evidence for ancient wet environments that were very acidic. The CRISM findings prompted the rover team to investigate the area where clay had been detected from orbit. There, they found an outcrop called "Whitewater Lake," containing a small amount of clay from alteration by exposure to water.
"Water that moved through fractures during this rock's history would have provided more favourable conditions for biology than any other wet environment recorded in rocks Opportunity has seen," researchers said.