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American scientists claim to have found evidence that suggests Mars had a warm and wet climate which could have supported life some 3.5 billion years ago.

A team, led by planetary geologists at Brown University, found mounds of a mineral deposited on a volcanic cone less than 3.5 billion years ago that speak of a warm and wet past, and may preserve evidence of one of the most recent habitable microenvironments on the red planet.

Observations by the National Aeronautics and Space Administration's Mars Reconnaissance Orbiter enabled the researchers to identify the mineral as hydrated silica which can be dissolved, transported and concentrated by hot water or steam - a dead ringer that water was present at some time.

Best evidence yet

The mineral and the mounds' location on the flanks of a volcanic cone provide the best evidence yet on Mars for an intact deposit from a hydrothermal environment — a steam fumarole or a hot spring, said the researchers.

Such environments might have provided habitats for some of Earth's earliest life forms, they hoped.

“The heat and water required to create this deposit probably made this a habitable zone,” said J. R. Skok, lead author of the study, published in journal Nature Geoscience.

“If life did exist there, this would be a promising spot where it would have been entombed - a microbial mortuary, so to speak.”

Favourable climate

No studies have determined whether Mars has ever supported life, but this finding adds to accumulating evidence that at some times and in some places, Mars hosted favourable climate for microbial life.

The deposit is located in the sprawling, flat, volcanic zone known as Syrtis Major and was believed to have been left during the early Hesperian period, when most of Mars was already turning chilly and arid.

“Mars is just drying out,” Skok said, “and this is one last hospitable spot in a cooling, drying Mars.”

Concentrations of hydrated silica have been identified on Mars previously, including a nearly pure patch found by NASA's Mars Exploration Rover Spirit in 2007. However, this is the first found in an intact setting that clearly signals the mineral's origin.

“You have spectacular context for this deposit,” Skok said. “It's right on the flank of a volcano. The setting remains essentially the same as it was when the silica was deposited.”

Bright deposits

Observations by cameras on the Mars Reconnaissance Orbiter revealed patches of bright deposits near the summit of the cone, fanning down its flank, and on flatter ground in the vicinity.

The Brown researchers partnered with Scott Murchie, of Johns Hopkins University Applied Physics Laboratory, to analyse the bright exposures with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the orbiter.

Hydrated silica identified by the spectrometer in uphill locations, confirmed by stereo imaging, indicates that hot springs or fumaroles fed by underground heating created these deposits. Silica deposits around hydrothermal vents in Iceland are among the best parallels on Earth.

“The habitable zone would have been within and alongside the conduits carrying the heated water,” Murchie said.