Opportunity finds more hints of Mars habitability

NASA's Opportunity rover on Mars has made one of its most significant discoveries to date after it identified a rock laden with clay minerals, more evidence that water once flowed on the red planet.
Clays form when water interacts with rock. Different types of water - acidic or neutral pH, saltiness - and different types of rock form different clays.
The aluminum-rich clays were detected by the rover in a rock called 'Esperance', Discovery News reported.
"What we have here is a very different chemistry," said planetary scientist Steve Squyres, with Cornell University.
"This is water you can drink. This is water that was probably much more favourable in its chemistry, in its level of acidity, for things like pre-biotic chemistry, the kind of chemistry that could lead to the origin of life," Squyres said.

"This is the most powerful evidence for neutral chemistry water that has been found by Opportunity," he added.

The golf cart-sized rover, which is closing in on its 10th anniversary on Mars, is heading toward a 180-foot tall stack of rock that may answer questions about when the planet transitioned from a warm, wet world to the acidic dry desert that appears today.
Opportunity spent three years driving across Mars to reach a large impact basin known as Endeavour Crater. Mineral maps complied from Mars orbiters showed it contained slight amounts of clay minerals.
Another rover, Curiosity, which landed on Mars in August, also found evidence of pH-neutral water changing the chemistry of a piece of bedrock in its Gale Crater landing site.

Curiosity is now headed to Mt Sharp, the 4.8-km-high mound of rock rising from the crater's floor that also shows signs of clay minerals.
As of Friday, the Opportunity rover, which was designed to last 90 days, has spent 3,331 days on Mars.
"I don't think there's anyone on this planet that would have imagined this rover lasting this long when we started almost 10 years ago," said Opportunity project manager John Callas, with NASA's Jet Propulsion Laboratory in Pasadena, California.