Mercury's surface was shaped by volcanoes - and it's shrinking, Nasa probe finds

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Mercury's surface was shaped by volcanoes - and it's shrinking, Nasa probe finds


By Daily Mail Reporter
Last updated at 12:54 PM on 04th July 2008



Volcanic activity forged the surface of Mercury while also making it shrink, scientists revealed today.

A NASA spacecraft discovered the smallest planet in the solar system has lost 3 miles of its 3,032 mile diameter. This is far more than scientists had expected.

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Mercury rising: The planet nearest the sun shows the circular marks of volcanoes

Messenger has begun to resolve some of the mysteries of Mercury, a sun-baked world about a third the diameter of Earth and only slightly larger than the moon. The car-sized spacecraft has seven scientific instruments on board and has measured magnetic activity.

In 1975, Mariner 10, the last spacecraft to fly past heavily cratered Mercury, sent back images showing smooth plains covering large parts of its surface.

But scientists have debated whether these plains were created by volcanic activity or by debris settling back onto the surface after space rocks collided with the planet.

But Messenger images from its January 14 fly-by provide strong evidence that volcanoes played a critical role in forming the planet's surface, according to geologist James Head of Brown University in Providence, Rhode Island.

The dramatic and large-scale volcanism probably took the form both of huge lava flows and violent eruptions, based on surface features seen in the images, Dr Head said.

He estimated that the volcanic activity occurred between three billion and four billion years ago, adding that there is no evidence of ongoing volcanism on the planet’s surface.

‘Everything we’ve seen so far would suggest that the activity on the surface dates from the first half of solar system history rather than the last half,’ Dr Head said.

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Shrinking: The smallest planet may have lost 3 miles of diameter during its history

The Caloris basin, with a diameter of 960 miles, is one of the solar system’s biggest impact craters, formed more than 3.8 billion years ago when a large space rock hit.

Messenger sent back images of a shield volcano with a distinct orange color about 60 miles wide on the southwestern edge of this basin that may be a source for the lava that formed smooth plains inside the basin.

These deposits look similar to basalt flows on the moon, but are very low in iron, representing an unusual rock type. The size of the plains imply the existence of large sources of magma in Mercury’s upper mantle, the scientists said.

Inside the shield volcano they detected a kidney-shaped vent with a bright halo around it very similar to halos formed by explosive eruptions on Earth and the moon.

In other findings also published in the journal Science, scientists said Mercury’s magnetic field originates in the planet’s outer core and is powered by the core’s cooling.

Messenger, which stands for Mercury Surface, Space Environment, Geochemistry and Ranging, was launched in 2004.

Nasa’s Mariner 10 flew past Mercury three times, mapping 45 per cent of its surface. Messenger has imaged about 20 per cent more and is due to fly by Mercury again this October and in September 2009 before starting a yearlong orbit in 2011.


Mercury's surface was shaped by volcanoes - and it's shrinking, Nasa probe finds | Mail Online