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Charon: Dwarf Planet Pluto's Largest Moon

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Published on May 9th, 2013 | by Yellow Magpie


Charon: Dwarf Planet Pluto’s Largest Moon

Charon Pluto’s Moon Photo By Lanthanum 138

Charon is the largest of Pluto’s moons. Despite being so far from the Earth we do know a little about this icy, potentially volcanic world.

Charon was first identified in 1978 by astronomer James Christy who noticed a slight bulge in an image of Pluto that was absent in another photograph. It was later resolutely proven in the mid-1980’s that Charon was Pluto’s moon.

Physical Characteristics

At 1,200 kilometres (750 miles) in width Charon is half the size of Pluto and substantially larger than its two sister moons, Hydra and Nix. Orbiting at a distance of over 19,000 kilometres (12,000 miles) it takes just under six and a half Earth-days to complete one trip.

Charon Pluto Moon Discovery Photo By NASA

Like Pluto and the Kuiper Belt objects, Charon is a cold world with a temperature of just 53 degrees Kelvin (minus 220 degrees Celsius). Charon is thought to be composed mainly of frozen water and ammonia.

The mass of Charon has been calculated to be just 11 per cent of Pluto. This suggests that the planet is roughly 55 per cent ice to 45 per cent rock. Pluto is nearly 70 per cent rock.

Charon’s Origins

Scientists originally believed that Charon was created as the by-product of a colossal impact with Pluto. The resulting icy debris would have coalesced to form the moon. This has been inferred from calculations that show that Charon is composed of much less rock than Pluto.

Charon, Hydra And Nix Orbiting Pluto Photo By H. Weaver (JHU APL), A. Stern (SwRI), and the HST Pluto Companion Search Team

Nonetheless, such predictive models do not account for the large amount of rock present in Charon’s core. It is now maintained that two Kuiper Belt objects collided and formed the two bodies now known as Pluto and Charon.


It is believed that Charon is home to cyrovolcanoes that emit melted solids such as ammonia. It is thought that tidal friction caused by the gravitational pull of Pluto is providing the energy for these eruptions.

Charon’s Name

James Christy named the newly discovered moon after his wife’s nickname and the Greek ferryman of dead souls. Unlike the Greek pronounciation, Charon is pronounced like Sharon.

Charon Artist's Impression Of Charon Viewed From Pluto Photo By NASA

Moon Or Dwarf Planet

Strictly speaking, as Charon’s barycenter (the centre of mass between two bodies) is outside of Pluto, Charon and the dwarf planet should be regarded as a binary system. That would make Charon a dwarf planet not a moon. However, as of yet it still retains satellite status.

New Horizons

So far the only images available to astronomers have been low-quality pictures taken from either Earth-based telescopes or the Hubble Space Telescope.

In 2015 the New Horizons spacecraft will make a flying visit past Pluto and its moons. With this brief encounter will come a minefield of information as well as detailed pictures of Charon’s surface.

Highly Recommended Reading

Check out Yellow Magpie’s Planet Neptune: The Mysterious Azure-Blue for more insight into this frozen region of the Solar System.

You may also wish to take a gander at The Solar System And Beyond: A Guide To The Cosmos.

Cosmos is a highly recommended book. It contains large, full-page pictures of the asteroids and writing on the subject by the highly competent author, Giles Sparrow.

For people living in Ireland or the United Kingdom, you can access: Cosmos from here.

For those who live in Canada, you can obtain: Cosmos here.

For Germany: Cosmos.

For France: Cosmos.

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