Did Mars have ancient oceans? Maybe not, new study says.

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.

By Pete Spotts,?Staff writer / September 11, 2012

Mars rover Opportunity, still working on Mars' Meridiani plains, snapped this picture of a rock formation on Aug. 23. Orbital investigation has identified a possibility of clay minerals in this area.

Arizona State Univ./Cornell Univ./JPL-Caltech/NASA/REUTERS/File

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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.

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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 meteor 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-a-likes 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.

The planet shows clear evidence for weathering and hydrothermal processes altering the surface in various areas, she adds. Indeed, Gale Crater and its looming Mt. Sharp, home to NASA's latest Mars rover, Curiosity, displays features that are hard to explain unless flowing or standing water was present on the surface.

The questions, she says are these: Which process dominated on a planetary scale at the time, "and what does that have to say about the overall climate?"

The team's eruptive proposition comes at a time when the notion of a persistent warm-wet-climate during the planet's first billion years has been taking hits in other ways.

For instance, a team of researchers from the US and France has modeled Mars' early climate, when the sun would have been weaker. They conclude that the climate would have been too cold to sustain liquid water on the surface for very long. Instead, over time water ice would migrate to the poles, forming vast ice caps. Limited warming could occur from large impacts or volcanic eruptions, releasing enough water to carve features seen on the southern highlands.

Source: http://rss.csmonitor.com/~r/feeds/science/~3/CacJJKljld4/Did-Mars-have-ancient-oceans-Maybe-not-new-study-says

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