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Moon and Mars

StarDate: 
January 31, 2016

One of the moons of Mars may be disintegrating right in front of our eyes. But it’s a slow process — the little moon is expected to survive for tens of millions of years.

Phobos is a potato-shaped rock that’s about 17 miles long. It orbits closer to its parent planet than any other known moon — only about 3700 miles away. At that height, it moves so fast that it rises in the west and sets in the east — twice a day.

Martian gravity pulls a little more strongly on the side closest to Mars than on the far side. That creates a powerful stress across the entire moon. Eventually, that will pulverize Phobos, perhaps creating a short-lived ring around the Red Planet.

And a recent study says we may already be seeing the moon start to shatter. Long rays and grooves stretch across Phobos. At first, scientists thought they were created by a powerful impact that blasted out a big crater. But the grooves don’t line up with the crater, so they probably weren’t caused by the collision.

Instead, the study says they may be the first signs that the little moon is being pulled apart. They suggest that Phobos is built like a pile of rubble wrapped in a thick coating. As Mars’s gravity pulls on Phobos, the interior shifts around, causing the surface coating to crack — early signs that the little moon is beginning to disintegrate.

Look for Mars quite close to the lower right of our moon at first light tomorrow. The planet looks like a bright orange star.


Script by Damond Benningfield, Copyright 2015

 

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