NASA's Mars rover Opportunity has scraped away at some of the oldest rock it's examined and found the strongest signs for water it has ever discovered over its 9.5-year mission, scientists for the Mars Exploration Rover project said Friday. The scrappy little rover is now heading down Endeavour Crater's rim to Solander Point, on what is in some ways a brand new mission, officials said.
"We consider it 'Sol 1' all over again for Opportunity," said John Callas, the mission's project manager at the Jet Propulsion Laboratory. A sol is a Martian day.
Just before leaving a spot called Cape York on its southbound journey, Opportunity examined a rock called Esperance using its X-ray spectrometer and microscopic imager, finding clear evidence that it held clay minerals that had been altered by water – a whole lot of it. It's a far cry from many of the previous findings on Martian moisture, said mission lead scientist Steve Squyres of Cornell University.
"We run around talking about 'water on Mars, water on Mars' -- in fact, what Opportunity has mostly discovered evidence for in the past was sulfuric acid on Mars," Squyres said. "What we have here is a very different chemistry.… This was water you could drink."
Esperance revealed signs of water whose favorable chemistry and low acidity made it potentially very friendly for life – paralleling recent results from NASA's Curiosity rover, whose drill pulled up clay minerals in Gale Crater that were rich in the chemical ingredients necessary for living things, including low acidity water.
But this evidence was not easy to uncover, Squyres pointed out. With what he called a "gimpy shoulder," Opportunity was unable to easily examine the minerals. Mars dust and debris obscured the true nature of the rocks, and a dust storm and solar conjunction – when the sun's bulk blocks lines of communication to Mars – interrupted their attempts. After several tries, they managed to use the rover's rock abrasion tool to scrape down to a clear, unaltered spot.
"This was really one of the most technically challenging and one of the most scientifically rewarding targets of our whole mission," Squyres said, calling the results one of the top-five most important findings of the 9.5-year mission. "This was really, really hard."
But Opportunity is moving on from Cape York; its few yards of exposed layers offer a relatively tiny slit of a view into the Red Planet's geologic history. Instead, the rover is heading down the crater rim to Solander Point, which will offer about 10 times as much layering. Solander could provide more evidence for the type of watery environment Mars was – and how those watery conditions changed over time.
Meanwhile, Curiosity is headed to a much bigger target – Mt. Sharp, the 3-mile-high mountain the middle of Gale Crater whose layers could provide a deep view into Mars's geochemical past.
Opportunity is going to have to hoof it down south to get to its destination before winter comes, officials said. Without the point's north-facing walls providing safe haven during the winter, it may be out of work.
But the rover, launched in 2003, is getting up in years, Callas said. It's been suffering from arthritis in its mechanisms and a little 'amnesia' in its flash memory.
So while Opportunity has outlasted its 90-day mission about 40 times over, the team isn't taking the rover for granted, he said.
"The rover could have a catastrophic failure at any moment," Callas said. "So each day is a gift."