Friday, 3 April 2015

Rover finds Mars had rich watery history - Columbus Dispatch

Debarjun Saha | 21:34 |

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By Los Angeles Times  •  Friday April 3, 2015 10:05 PM

Climbing up Mount Sharp in the middle of Gale Crater, NASA's Mars rover Curiosity has discovered a two-tone vein of minerals that reveals multiple episodes of water flowing through rock — even after the lake that once filled the bottom of the crater had ceased to be.

The discovery points to an even more complex, and perhaps long-lived, watery environment on the Red Planet than previously contemplated.

"Not only does this help us try to understand the chemistry of the rocks that we measure in the region, but on a different sort of scale it tells us that fluids were around on Mars for a long time," said Linda Kah, a sedimentary geologist at the University of Tennessee-Knoxville and a member of Curiosity's science team.

The duotone deposits, at a spot called Garden City, sit 39 feet above the lower edge of the Pahrump Hills outcrop, which is part of the basal layer of the 3-mile-high Mount Sharp. They feature both light and dark regions. They rise about 2 1/2 inches above the rock surface like ridges, because the rock that once surrounded them has worn away. Such veins are formed when fluid flows through cracks in a rock and leaves some minerals behind.

Most veins have been bright and light-colored, Kah said, often filled with calcium sulfate. On Earth, such mineral deposits are often associated with salty water. But the dark deposits were somewhat unexpected, she said.

The dark parts often seem to line either side of the white veins, like an ice-cream sandwich — a description that Kah's 10-year-old son Douglas offered while looking over his mother's shoulder at images of the deposits.

"They're incredibly gorgeous," she said.

The two different tones are scientifically telling. Researchers look at Martian rocks in part to see how water (and the stuff in the water) might have affected a particular rock during a particular era. But if the same rock is getting soaked with very different kinds of water sources over time, then it might show a confusing mix of traits from a long period in which the environment dramatically changed over and over.

That's why the mineral veins are so helpful. They offer a snapshot of at least one individual era in the Red Planet's history — and, in this case, three, scientists say.

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