PARIS (AFP) — Water bathed the surface of southern Mars for millions of years, helping to create an environment theoretically capable of nurturing life, according to a new study into the planet's mysterious oceans.
Scientists at Brown University in Rhode Island used an instrument aboard a US spacecraft, the Mars Reconnaissance Orbiter, to hunt for traces of phyllosilicates, or clay-like minerals that preserve a record of water's interaction with rocks.
They found phyllosilicates in thousands of places, in valleys, dunes and craters in the ancient southern highlands, pointing to an active role by water in Mars's earliest geological era, the Noachian period, 4.6 to 3.8 billion years ago.
"These results point to a rich diversity of Noachian environments conducive to habitability," the authors conclude.
An intriguing find was of deposits in the pointed peaks at the centre of craters. These peaks are generally taken to be underground material thrown up by an impacting asteroid or comet.
For water to be present in such peaks, it must have been present as much as five kilometres (three miles) below the planet's surface, the paper suggests.
"Water must have been creating minerals at depth to get the signatures we see," head researcher John Mustard, a professor of planetary geology, said in a press release.
The subsurface phytosillicates were formed at relatively low temperatures, of between 100 and 200 degrees Celsius (212-392 degrees Fahrenheit), which implies that Mars was not only wet but also relatively temperate at the time.
"What does this mean for habitability? It's very strong," Mustard said. "It wasn't this hot, boiling cauldron. It was a benign, water-rich environment for a long period of time."
The paper, which appears on Thursday in the London-based science journal Nature, is the latest assessment to conclude that Mars was once awash with water, one of the ingredients for life.
Close-up investigations by US landers and imaging from orbiters have also suggested that frozen water may lie close to the surface in some areas today, and possibly in abundance.
Still unclear is what happened to the oceans. The leading theory is that the planet's once-thick atmosphere began to thin, causing the precious liquid to evaporate into space. Only a thin atmosphere, consisting overwhelmingly of carbon dioxide, remains today.
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