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Why does Iapetus have two colours?

7 Sep 2015, 13:42 UTC
Why does Iapetus have two colours? NASA/JPL/Space Science Institute
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Why does Iapetus have two colours?
Chris, South Africa

Iapetus is the third largest satellite of Saturn, and it is the largest object in the solar system not in hydrostatic equilibrium. Iapetus is known for its colour dichotomy. It has a dark side and white side, and it is often called the Yin Yang moon. This fact was known since its discovery in 1671 by the Italian Astronomer Giovanni Cassini. During his first few observations, Cassini was able to see it only on one side of Saturn, and when he eventually observed it on both sides, he discovered that one side was much dimmer than the other.
Although the peculiar coloration of Iapetus has been known for centuries, the mystery has only been solved very recently, just in 2009. There is no technical or complex explanation for what happens to Iapetus. The closest description for it is: bugs on a windshield.
Iapetus is tidally locked to Saturn. Like our own Moon, showing always the same face. Iapetus has a side always facing forward in the direction of motion and side facing away. So, one side is constantly exposed to infalling material just like bugs on the windshield of a fast ...

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