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Evening Mercury

December 11, 2016

The little planet Mercury is putting in a brief evening appearance right now. You need to look at just the right time to see it, though. And the view is best from southern latitudes; from the north, you might not be able to see it at all.

Mercury is the smallest planet in the solar system — only about half again the diameter of the Moon. And its surface looks a lot like the Moon’s — it’s covered with impact craters, mountains, and volcanic plains. And there’s evidence that the surface is still being sculpted by Mercury itself.

Mercury’s interior has been cooling since the planet was born. As it cools, it shrinks. That causes the crust to shrink as well.

Scientists have seen evidence of that shrinkage in the form of scarps — giant cliffs that can be miles high and hundreds of miles long.

A recently concluded mission to Mercury also found some smaller scarps. Such small features are quickly erased by meteorite impacts. The fact that they still exist means that they formed fairly recently. They probably formed as the crust continued to cool and shrink — although at a much slower rate than when Mercury was young. They show that Mercury is still geologically active — rattled by its ever-shrinking crust.

Look for Mercury quite low in the southwest about 30 to 45 minutes after sunset, far to the lower right of brilliant Venus. Mercury looks like a fairly bright star, but you may need binoculars to pluck it from the fading twilight.


Script by Damond Benningfield


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