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Farmers Almanac
The 2014 Farmers Almanac
Farmers' Almanac

Charon: Moon or Dwarf Planet?

Charon: Moon or Dwarf Planet?

When Pluto was downgraded to a dwarf planet in 2006, astronomers began thinking in a new way about its largest moon, Charon.

Charon was the first of Pluto’s four moons to be discovered, and its largest. Charon is believed to be more than half the diameter of Pluto. Because Charon is so large in comparison to Pluto, the two bodies actually revolve around one another, instead of Charon revolving around Pluto, as once believed. For this reason, some astronomers have proposed upgrading Charon to the status of dwarf planet.

Here are some more interesting facts about Charon:

- Charon was first discovered on June 22, 1978, by astronomer James Christy at the United States Naval Observatory Flagstaff Station. The moon (or dwarf planet, as the case may be) was first seen as a bulge appearing on some photos of Pluto. The bulge wasn’t confirmed to be a moon until nearly a decade later, when the two bodies entered a period of eclipsing one another.

- The surface of Charon probably a rocky core surrounded by an icy outer layer, similar to Pluto. The moon is believed to feature numerous active volcanoes that spew ammonia-rich water.

- Astronomers do not know the composition of Charon’s atmosphere, or if it even has one. Many unknown details will become clearer in 2015, when New Horizons, the first spacecraft sent to explore Pluto and its moons, arrives at its destination.

- Charon is about 750 miles in diameter, just over half the size of Pluto.

- It takes Pluto and Charon about 248 Earth years to complete one orbit around the Sun, and about 6.5 Earth days to revolve around one another.

- The average distance between Charon and Pluto 12,160 miles.

- Charon takes its name from the mythological ferryman who carried the dead across the River Styx to the realm of Hades (Pluto to the Romans), god of the underworld. Christy chose it because of its similarity to a nickname he had for his wife, Charlene.

- The average surface temperature on Charon is around -390° F, a little colder than Pluto’s.

- In addition to Charon, Pluto has three other moons, Nix, Hydra, and the as-yet-unnamed P4 (S/2011 P 1). Because Pluto and Charon revolve around one another, these other three moons orbit both bodies.

- Charon cannot be seen with the naked eye, or with most consumer grade telescopes. It can really only be observed with some of the most powerful telescopes in the world. The first clear images of it were taken from space by the Hubble Space telescope.

Whether Charon remains a moon or is eventually upgraded to a dwarf planet, it remains one of the most interesting objects in our solar system.

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