During its long lifetime, the Moon has been beaten, battered, and biffed countless times by collisions with giant boulders. The impacts have scarred the lunar surface with craters, jumbled mountains, and plains of volcanic rock -- sometimes all in one feature.
An example is a feature known as Mare Orientale -- the "eastern sea." Because of a change in terminology, it's actually on the Moon's western edge. In fact, most of it is out of view on the lunar farside.
But pictures from spacecraft in lunar orbit reveal a striking profile: Mare Orientale looks like a bullseye. It consists of a circular patch of dark rock, surrounded by three rings of mountains. The whole system spans almost a thousand miles.
Mare Orientale formed about 3.8 billion years ago, when a mountain-sized asteroid slammed into the Moon. A massive shockwave rippled out from the impact like the ripples from a stone dropped into a pond. In this case, though, the ripples moved through solid rock. They piled up the rock in front of them, creating three ring-shaped mountain ranges.
Molten rock bubbled up to fill the hole left by the impact. Over time, the rock cooled to form the smooth plain known as Mare Orientale.
Most of the time, Mare Orientale is out of sight beyond the Moon's western limb. But the Moon appears to wobble back and forth a bit, so later this month, part of Orientale will just peek into view -- the scar of a cosmic beat-down.
Script by Damond Benningfield, Copyright 2008
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