July 6, 2010

Probe Provides Clues About Moon’s Mantle

The Moon's geological past could be better understood by a mineral that Japanese astronomers report they have found.

Using an instrument-loaded probe - Kaguya - placed in orbit around the lunar body in 2007, the team of scientists found abundant sources of the mineral in concentric rings in three distinct crater regions.

Olivine, as the mineral is known, is believed to be a revealing sign of mantle -- the deep inner layer of iron- and magnesium-rich rock that lies beneath the Moon's crust.

One of the top theories is that the Moon was created around 4.5 billion years ago after it was ripped from the Earth when our planet was struck by a gigantic object from outer space.

As the material formed into a ball, the surface gradually cooled, forming a crust made of light-colored aluminous mineral, feldspar, which flowed in a dense, molten liquid.

The data taken from Kaguya adds to the "lunar magma ocean" theory.

It suggests that once the crust had formed, there was a massive overturn in the fiery liquid beneath. Olivine-rich mantle worked its way from deep within the lunar depths to within the base of the crust.

At the craters sampled by the probe -- the South Pole-Aitken, Imbrium and Moscoviense impact basins -- the Moon's crust is very thin, and the olivine mantle may have been exposed by asteroids that impacted the lunar surface, the paper suggests.

The Lunar crust is believed to be thicker than Earth's, averaging around 45 miles in depth, compared to Earth's 20 to 30 miles thick.

The structure and origins of the Moon's mantle have been debated by astrogeologists for some time. Moon rocks collected and returned by the Apollo missions shed no light on the question, as they were all from lunar crust. As a result, the idea of the existence of a mantle was quite sketchy for decades.

The study is published online by the journal Nature Geoscience. The study was led by Satoru Yamamoto of the National Institute for Environmental Studies in Tsukuba.


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