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Did Mars have ancient oceans? Maybe not, new study says. (+video)

Clay deposits on Mars have been seen as evidence that the planet once had a warm, wet climate. But a new study suggests the clay could have volcanic origins.

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Others have noted that water-carved features in widely spaced locations formed at vastly different times, weighing against a single span of wet climate as the source of flow that formed them.

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Dr. Ehlmann and Dr. Meunier had teamed up on research last year that indicated clays could form through the interaction of water leaching through hot rocks. The clays resulting from hydrothermal activity would tend to show composition similar to clays formed at the surface.

But, Ehlmann recalls, Meunier mentioned the volcanic process, in which water trapped in lava interacted with the superhot material as it cooled and released its gases. Where water was involved, the interaction formed clays that filled nooks and crannies in the cooling rock. And its chemical signature was similar to the clays formed on the surface and via hydrothermal action. The evidence came from volcanic clays found in French Polynesia and in Brazil, which had experienced ancient eruptions where magma would flood the landscape from fissures in the rock.

Ehlmann offered that such clays wouldn't be abundant enough to yield a spectral signature orbiters could pick up. Meunier and colleagues went back to the lab, examined the samples with spectrometers similar to those on the orbiters, and found that such clays were in fact readily detectable from orbit.

In addition, the team found evidence for volcanically generated clays in some of the Martian meteorites that researchers have found on Earth, although the meteorites are younger than the period in question for forming the ancient, widespread clays that have intrigued researchers over the past five years or so.

The research paper "is pretty convincing," says Caleb Fassett, a planetary scientist at Mount Holyoke College in South Hadley, Mass.

For now, the notion that a volcanic origin could be the dominant source for clays widely seen as rain gauges for an ancient climate is a hypothesis, one that makes firm predictions about subtle differences in composition the clays should exhibit compared with the rock layers around them.

But such measurements will require additional Mars landers or rovers with the right capabilities near clay deposits in various locations on Mars. As a result, the work could help guide decisions on future landing sites, notes Brown University planetary scientist James Head III – budgets willing.

IN PICTURES: Exploring Mars

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