Saturday, March 6, 2010

134340 Pluto, and his little brother Charon


Pluto, formally known as a Planet, has been recategorized by the International Astronomical Union on August 24, 2006 as a dwarf planet. Although no longer considered an upstanding member of the solar system (to borrow a phrase from 2 Skinnee J's), Pluto is now the largest member of the Kuiper belt. So it's not all bad for Pluto. Rather than being the smallest fish in a sea filled with giants like Jupiter, Pluto is now the largest member of a smaller sea.

But what about Charon. Charon is the largest of Pluto's moons, or rather that's what Charon used to be. Since Pluto is no longer a planet, it's inaccurate to call Charon a moon, a nickname for natural satellites such as the Earth's Moon that orbit planets.

At times Charon was even referred to as a double planet with Pluto because of its size compared to Pluto, just over half the size of Pluto. Indeed, Charon and Pluto are so close that neither actually rotates around the other. Instead they are deadlocked in an icy stare, with the same surface of each always facing the other.

Charon even used to have the unique characteristic among moons of being the largest moon in the solar system proportional to the planet which it orbited.

But no more. When Pluto lost it's status as a planet, Charon lost it's moonhood. Charon is now just another member of the Kuiper belt, and will always be second fiddle to Pluto in that sea. Even the International Astronomical Union hasn't bothered to define Charon's status, though if Pluto gets to be a dwarf planet it seems obvious that Charon should have the same designation.

For now, all we can do is wait until July 2015 when NASA's New Horizons robotic spacecraft will arrive at the Pluto-Charon system. Maybe then Charon will get the recognition it deserves. Though it seems likely that Pluto will still be hogging the spotlight.