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Opportunity, now moving to another target 1.5 miles away, has found evidence that some of the water on Mars was once drinkable.
Before trekking off last month, Opportunity used a grinder to scrape away the top layer of a light-colored rock for a peek inside. The rock was so lumpy and covered with crud that it took the rover several tries to crack open its secrets. Unlike other rocks that Opportunity inspected during the past nine years, the latest told a different story: It contained clay minerals, a sign that water coursed through it, and formed in an environment that might have been suitable for microbes. Previous rock studies by Opportunity pointed to a watery past on Mars, but scientists said the water was acidic.
“This is water you can drink,” said mission chief scientist Steve Squyres of Cornell University.
More details here, noting that this water comes from an earlier time on Mars, when the planet’s environment was more benign.
So the rover has now sampled both sides of the momentous planetary transition from a wet, benign environment more than 4 billion years ago to a colder, drier, harsher one since then