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Moon and Companions

January 6, 2016

The Moon is a battered landscape, scarred by four-and-a-half billion years of collisions with space rocks. The largest of these scars is a dark basin about 1500 miles wide and eight miles deep — the biggest impact feature in the entire solar system. And some of its violent history is told in a mound on the basin floor.

South Pole-Aitken basin formed when a massive asteroid slammed into the lunar surface. The impact gouged a wide crater, which then filled with molten rock. Most of the basin is on the lunar farside, so it’s visible only to spacecraft.

Mafic Mound is one of the many features on the basin floor. It’s about 50 miles wide and a half-mile high. And its composition is a little different from that of the surrounding landscape.

Researchers from Brown University studied observations of the mound from several craft. They concluded that it likely formed in the aftermath of the impact.

One possible scenario says that the impact created a deep lake of molten rock. As the rock cooled and hardened, it shrank. That squeezed pockets of still-molten rock like a toothpaste tube, the researchers say, forcing some of the liquid rock to the surface. That rock should have contained a lot of calcium-rich minerals — matching the composition of Mafic Mound.

And the Moon is in good view at dawn tomorrow. Venus, the “morning star,” stands to its upper right, with the fainter planet Saturn between them. And Antares, the heart of the scorpion, is farther to the right of the Moon.


Script by Damond Benningfield, Copyright 2015

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