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Mars' surface once had lakes and rivers

A spacecraft flying high above Mars has found evidence that water flowed on the planet in such abundance billions of years ago that lakes and rivers existed all over its surface, scientists say.

Images sent back to Earth from the Mars Reconnaissance Orbiter show vast quantities of water-bearing clays on Mars' surface, particularly in the planet's highlands.

So it was water, water everywhere in Mars' earliest days, between 4.6 billion and 3.8 billion years ago, said planetary geologists John Mustard at Brown University and Scott Murchie at Johns Hopkins. And that watery environment, they said, must have meant the planet was habitable long ago – a possibly suitable place for life.

Mustard and Murchie, along with a team of three dozen colleagues, published a full report on the new signs of water in the journal Nature on Thursday.

Murchie said he and his colleagues now have “a high degree of confidence” that they have seen evidence of the existence of water in widespread clay mineral rocks that could have been formed only by flowing water and probably large lakes.

“The water was not only there, but it was there abundantly and remained long enough to affect the mineralogy of the planet,” he said. He also said it could have been there at a time comparable to Earth's early days, “when the first living organisms emerged and left their fossils that we find today.”

In a statement, Murchie said, “The big surprise is how pervasive and long-lasting Mars' water was, and how diverse the wet environments were.”

The clay mineral rock most likely was blasted to the surface from underground by huge meteorites, the scientists said, noting that huge deposits of the mineral probably remain beneath the surface.

In an earlier report, one team member, Brown graduate student Bethany Ehlmann, reported that the same spacecraft had found the water-formed clay minerals in an old delta on a Martian crater the size of Lake Tahoe. She proposed that the crater, named Jezero, would be an ideal landing site for next year's hugely sophisticated Mars Science Laboratory, a wide-ranging rover that will push the search for water even further.

“Water must have been creating minerals at depth to get the signatures we see,” said Mustard, Murchie's principal colleague. “What does this mean for (the planet's) habitability? It's very strong. It was a benign, water-rich environment for a long period of time.”

The clay minerals are called phyllosilicates, and they were detected by a specialized instrument aboard the orbiter called the Compact Reconnaissance Imaging Spectrometer for Mars, dubbed CRISM.

The high-tech imaging system, the most sophisticated sent to Mars to date, has not only sent back pictures of the water-bearing clay minerals, but has also identified different types of the phyllosilicates, including one form of hydrated silica known on Earth as opal.

Ehlmann, who spotted her clay minerals in the Martian crater Jezero, said a system of river channels long ago must have eroded them out of the highlands and concentrated them in a delta that in turn filled a lake bed where the standing water must have persisted for thousands of years.

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