Tuesday, October 30, 2012

Moon Suffered Enormous Collision

The largest dark spot on the moon, known as the Ocean of Storms, may be a scar from a giant cosmic impact that created a magma sea more than a thousand miles wide and several hundred miles deep, researchers say.

These findings could help explain why the moon's near and far sides are so very different from one another, investigators added.

Scientists analyzed Oceanus Procellarum, or the Ocean of Storms, a dark spot on the near side of the moon more than 1,800 miles wide.

The near side of the moon, the side that always faces Earth, is quite different from the far side, often erroneously called the moon's dark side (this side does in fact get sunlight — it simply never faces Earth). For example, widespread plains of volcanic rock called "maria" (Latin for seas) cover nearly a third of the near side, but only a few maria are seen on the far one.

. . . The researchers analyzed the composition of the moon's surface using data from the Japanese lunar orbiter Kaguya/Selene. These data revealed that a low-calcium variety of the mineral pyroxene is concentrated around Oceanus Procellarum and large impact craters such as the South Pole-Aitkenand Imbriumbasins. This type of pyroxene is linked with the melting and excavation of material from the lunar mantle, and suggests the Ocean of Storms is a leftover from a cataclysmic impact.

This collision would have generated "a 3,000-kilometer wide magma sea several hundred kilometers in depth," lead study author Ryosuke Nakamura, a planetary scientist at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, told

The investigators say that collisions large enough to create Oceanus Procellarum and the moon's other giant impact basins would have completely stripped the original crust on the near side of the moon. The crust that later formed there from the molten rock left after these impacts would differ dramatically from that on the far side, explaining why these halves are so distinct.

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