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Moon and Spica

StarDate: 
January 29, 2016

The gibbous Moon passes over a bright star at dawn tomorrow. Spica, the leading light of Virgo, shines just a few degrees below the Moon, so you can’t miss it.

Something else you can’t miss is the dark markings on the lunar surface. The biggest is near the left edge of the lunar disk — the Ocean of Storms. In fact, it’s the biggest of all the Moon’s dark markings, so it’s the only one known as an “ocean” — the others are called seas or other smaller bodies of water.

Of course, there’s not a drop of liquid water anywhere in the Ocean of Storms. Instead, it’s a volcanic plain — a bed of ancient rock.

There’s been some disagreement lately over how it formed. One group of scientists said it was the result of processes within the Moon itself. Another said it was the result of a giant impact.

The first group found traces of cracks in the crust around the Ocean of Storms. Those cracks could have formed as the young Moon cooled and its crust contracted. The cracks then allowed molten rock from below to bubble to the surface.

The other group used a Japanese satellite to measure the composition of the rock. Its observations suggested an impact origin. A giant space rock slammed into the young Moon, gouging out a wide basin, which then filled with molten rock from below. That scenario matches the generally accepted idea for the creation of most of the Moon’s volcanic plains — dark scars left over from the Moon’s violent past.


Script by Damond Benningfield, Copyright 2015

 

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