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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.

Mysterious features on slopes hint there could be water flows on Mars.
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Global deposits of ancient, clay-rich rocks on Mars ­– widely seen as evidence of a wetter, warmer, climate in the planet's past – may not be all they're cracked up to be.

A new study posits that the clays, which often form on Earth either from the action of water on surface rocks or from the passage of hot water through porous underground formations, could just as easily have formed from cooling lava, bearing no witness whatsoever to a warm, wet climate in Mars' past.

The study doesn't rule out the sporadic appearance of water in some places on the Martian surface – perhaps from near-surface water ice melted by the heat of a meteoric impact or volcanic eruptions. Some clays could well have been formed through the weathering action of water released in these ways.

But if Earth look-alikes and evidence from some Martian meteorites are any indication, a purely volcanic origin for much of Mars' clay-enriched deposits is as plausible as invoking a warm, wet climate during the planet's first billion years, according to the research team, led by Alain Meunier, a researcher at the University of Poitiers in France.

The bottom line: "Mars is a diverse place, and all of these processes happened at different points on the planet," says Bethany Ehlmann, a planetary scientist at the California Institute of Technology in Pasadena and a member of the team reporting the results Sunday in the journal Nature Geoscience.

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