1 billion year old crater on Mercury proof of recent volcanism.

Byline: ANI

London, October 22 (ANI): A NASA spacecraft has discovered a new crater on Mercury that may have been geologically active as recently as a billion years ago, which indicates recent volcanism on the planet.

According to a report in Nature News, the crater was discovered by NASA's Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft on its latest fly-by of the innermost planet of the Solar System.

"It's the youngest terrain we've yet seen on Mercury," said Clark Chapman, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, and part of the MESSENGER mission team.

The crater, about 260 kilometres in diameter, does not have a formal name, but because it looks similar to a basin named Raditladi, discovered in early 2008, it has been informally dubbed 'Twin'.

Both craters have bull's-eye structures, with a pair of concentric walls separating inner and outer sections of the crater floor.

The main difference is that the inner ring of Twin is pocked by very few small craters, indicating that it has not been exposed to meteor bombardment for as long as Raditladi.

There's only one thing that could resurface part of the floor of an impact crater that recently.

"That's just absolute proof of volcanism," Chapman said. "It's hard to say, but it could be less than a billion years old," he added.

Previously, scientists had thought that Mercury's period of volcanic activity ended more than three billion years ago.

Although the areas around Raditladi's inner and outer rings have roughly the same number of craters, Twin's outer ring has three times more craters than its inner one.

"That suggests that the crater might have seen two successive stages of volcanic activity," said Chapman.

The MESSENGER scientists are also seeing features that seem to be volcanoes, and include smooth areas that could be the residues from pyroclastic flows - outbursts of hot rocks and gas.

Such flows are a surprise because they come from magma that is rich in volatile compounds.

"We're getting an intriguing look that even as close to the Sun as Mercury there may be some process for delivering and retaining volatiles to the interior that we did not appreciate," said Sean Solomon, of the Carnegie Institution of Washington.

Meanwhile, MESSENGER is cruising toward its final rendezvous with Mercury, on March 18, 2011, when it will brake into orbit and begin detailed mapping. (ANI)

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