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Pluto’s Moons

StarDate: 
July 8, 2015

In 1978, astronomer James Christy was looking at some photographs of Pluto when he noticed something odd: The little world seemed to have a “bump” on its side. That bump turned out to be a moon. Christy named it Charon, for the character who ferried souls to Hades, the dominion of the god Pluto.

It turns out that Charon is about half again as wide as Pluto itself. In fact, many scientists consider Pluto and Charon to be a double planet.

Charon has several things in common with our own moon. Most important, it probably formed in much the same way as the Moon did — from a “big whack.”

A large body probably slammed into Pluto billions of years ago, blasting debris into orbit around it. Much of this material then coalesced to form Charon. In Pluto’s case, that process apparently left some small chips that are still around today — several tiny moons beyond Charon.

Also like Earth’s moon, Charon is “locked” so that the same side always faces its parent world. But Pluto is locked as well. So the length of a day on Pluto is exactly the same as the time it takes for Charon to make one turn around it — about six-and-a-half Earth days.

And there’s one more similarity between the Earth-Moon and Pluto-Charon systems. The larger bodies are colorful — Earth is blue, and Pluto is fairly red — but the moons are both grey. So like our moon, the surface of Charon could be quite different from that of its parent world. More tomorrow.

Script by Damond Benningfield, Copyright 2015

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