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From stuck to in luck

Sand-trapped JPL rover finds more evidence of a once-wet Mars.

October 29, 2010|By Joe Piasecki, The Valley Sun
(NASA/JPL )

The Mars rover Spirit has been stuck in sand for some 18 months, but that hasn't stopped JPL scientists from making new discoveries.

Analysis of soil layers that the rover exposed while trying to break free of a Martian sand trap has turned up new evidence that liquid water once existed on the Red Planet.

Just below the planet's dusty surface, water-soluble minerals were found layered below less-dissolvable minerals, leading the rover team to hypothesize that the water-soluble minerals were dissolved and then deposited by water percolating down from melting ice or snow.

"We see this kind of gradient of change in these trace elements as you go down into the soil over the few tens of centimeters we had to look at," said Bruce Banerdt, the JPL-based project scientist for the Mars Exploration Rover Project.

The evidence of liquid water that scientists have previously detected on Mars rocks could date back to as far as several billion years ago. These current findings, however, would place water on the planet much more recently — on the geologic timescale, at least.

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"It couldn't have been too long ago, because it's all in looser dirt, like the kind you would kick around in your backyard. And you wouldn't expect loose dirt to be lying there undisturbed for millions of years," Banerdt said.

There is no evidence that liquid water would exist on Mars today because temperatures there seldom remain above freezing for long and the planet's thin atmosphere would cause liquid water to instantly vaporize.

Tilts of the planet's axis that occur at intervals of tens and 100s of thousands of years do, however, warm up parts of the planet's surface occasionally.

"We have a rough relative chronology consistent with wet, warm conditions early in Mars history, then the planet becoming very dry and cold, but then we also know of variations on the current climate where there are possible conditions [to support water in liquid form] as the axis of the planet wobbles around," said Banerdt. "Our hypothesis is that tens to hundreds of thousands of years ago, the climate on Mars could have been a little warmer and support precipitation or condensation on the surface that was stable enough to percolate into these soil layers."

Perhaps even more dazzling than this potential rewrite of Mars' history is the unexpected lifespan of the rovers Spirit and Opportunity.

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