Charon
What is Charon?
Moons· Diameter 1,212 km. Pluto's largest moon, more than half Pluto's width. The two always keep the same faces turned toward each other as they circle a point between them, so they are sometimes called a double dwarf planet.
Orbit and size
| Diameter | 1,212 km (half of Pluto) |
|---|---|
| Distance from Pluto | 19,600 km |
| Orbit | 6.39 d |
| Note | mutually tidally locked pair |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Parent planet and sibling moons
Mordor, the red cap on Charon's north pole
A reddish-brown patch covers Charon's north pole, nicknamed 'Mordor' after the land in The Lord of the Rings. Scientists explain that it comes from Pluto. Some of the methane gas escaping from Pluto's atmosphere drifts over to Charon and freezes onto its very cold pole. Over a long time, ultraviolet light changes that methane into reddish organic material.
Charon's long winters make this possible. Pluto and Charon take 248 years to go around the Sun, so once winter comes, a pole goes without sunlight for more than a century. The temperature drops so low that incoming methane freezes and builds up. When spring sunlight returns, most of the methane escapes again, but the reddened material stays behind and slowly thickens.
Along Charon's equator runs a belt of canyons more than 1,000 km long. The deepest parts may reach 9 km, several times deeper than the Grand Canyon. Scientists think an ocean inside Charon froze and expanded, pushing on the outer shell until it cracked. It works like a glass bottle full of water that breaks when the water freezes.
The moon in depth
Charon was discovered in 1978 by James Christy of the US Naval Observatory, who noticed a slight bump on one side of Pluto in photographs. At 1,212 km across, Charon is more than half as wide as Pluto (2,377 km) and has 12 percent of Pluto's mass. It is so large for a moon that the point the two circle together lies in empty space outside Pluto. That is why the pair is sometimes called a double dwarf planet.
Pluto and Charon always show each other the same side. From one half of Pluto, Charon hangs in the same spot in the sky as if frozen in place; from the other half it never appears at all. The two are 19,600 km apart and go around together once every 6.39 days. Following Pluto in the orbit view shows the pair turning face to face.
When the New Horizons spacecraft flew past in 2015, Charon turned out to have a far more eventful past than expected. Huge canyons run along its equator, and a wide, smooth plain stretches across the south. The moon is not active today, but these are signs of major changes inside it long ago. Besides Charon, Pluto has four small moons, Nix, Hydra, Kerberos and Styx, which circle the Pluto–Charon pair together.
Frequently asked
- How big is Charon?
- The diameter of Charon is 1,212 km (half of Pluto).
- How far is Charon from Earth?
- The distance from pluto of Charon is 19,600 km.
- What is notable about Charon?
- The note of Charon is mutually tidally locked pair.
- Which planet does Charon orbit?
- Charon orbits Pluto.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.