Min­eral veins on Mars hold clues to planet’s wa­tery past

NASA’s Cu­rios­ity rover finds signs that mi­cro­bial life, if it ever ex­isted, could have thrived.

Los Angeles Times - - THE WORLD - By Amina Khan amina.khan@la­times.com Twit­ter: @am­i­nawrite

Climb­ing up Mt. Sharp in the mid­dle of Gale Crater, NASA’s Mars rover Cu­rios­ity has dis­cov­ered two-tone veins of min­er­als that re­veal mul­ti­ple episodes of wa­ter flow­ing through rock — even af­ter the lake that once filled the bot­tom of the crater dis­ap­peared.

The rover’s dis­cov­ery points to a very dif­fer­ent kind of wa­tery hab­it­able en­vi­ron­ment from what Cu­rios­ity has found be­fore — one that may also have been hab­it­able for mi­cro­bial life, if it ever ex­isted on the Red Planet.

“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 duo-tone de­posits, at a spot called Gar­den City, sit about 39 feet above the lower edge of the Pahrump Hills out­crop, which is part of the basal layer of the 3mile-high Mt. Sharp.

The de­posits fea­ture both light and dark re­gions. They rise about 2.5 inches above the rock sur­face like ridges, be­cause the rock that once sur­rounded them has worn away. Th­ese kinds of 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.

“There’s some­thing very dif­fer­ent about th­ese veins than what we have seen prior,” Kah said.

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

“I think they’re in­cred­i­bly gor­geous and beau­ti­ful,” she said.

The two tones are sci­en­tif­i­cally telling. Re­searchers look at Mar­tian rocks in part to see how wa­ter (and the stuff in the wa­ter) may 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 may show a con­fus­ing mix of traits from a long pe­riod in which the en­vi­ron­ment dramatically changed over and over again.

That’s why the min­eral veins are so help­ful. The de­posits in the cracks can look very dif­fer­ent from the sur­round­ing rock be­cause they were formed much later than the rock it­self.

So while the rock’s chem­istry and min­er­al­ogy will have been af­fected by mul­ti­ple en­vi­ron­ments, the min­eral veins of­fer a snap­shot of at least one in­di­vid­ual era in the Red Planet’s his­tory.

In this case, the min­eral veins ac­tu­ally of­fer snapshots of three en­vi­ron­ments. At first the sci­en­tists thought there were two epochs, rep­re­sented by the light and dark de­posits, but it turns out that some dark spots are chem­i­cally dif­fer­ent from other dark ar­eas.

“It was re­ally very ex­cit­ing for us,” Kah said. “Now we’ve just added com­plex­ity, so it makes it more fun to fig­ure it out in the long run.”

Cu­rios­ity, which landed on Mars in 2012, has al­ready found en­vi­ron­ments with the right chem­i­cal in­gre­di­ents for life, as well as not-too-salty, not-too-acidic wa­ter. It has also turned up ev­i­dence of a lake that may have drained and filled over time.

The sci­en­tists think that this en­vi­ron­ment ex­isted long af­ter the lake that once filled the bot­tom of Gale Crater dried up for good, and that th­ese de­posits were cre­ated by wa­ter un­der a sig­nif­i­cant amount of rock — enough to ex­ert the kind of pres­sure that would force the fluid to push through cracks in the stone.

It’s also un­clear how hot or cold or acidic or salty this wa­ter was; the fluid’s chem­istry could have been very dif­fer­ent from the po­ten­tially potable liq­uid in that long-gone lake.

But it’s still quite pos­si­ble that mi­cro­bial life, if it ever ex­isted, could have thrived in this en­vi­ron­ment, just as they thrive in the rock frac­tures at the hot springs of Yel­low­stone Na­tional Park, Kah said.

NASA

THE ROVER found the two-tone min­eral de­posits at a spot called Gar­den City on Mars’ Mt. Sharp.

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