Charon Moon Facts

Pluto is a dwarf planet, and is the only one that has a moon that is so large that it is almost the same size as Pluto.

Charon Moon Profile

Discovered By:James Christie June 22, 1978
Diameter:1,207.2 km
Mass:1.55 × 10^21 kg (2.1% Moon)
Orbit Distance:17,536 km
Pluto Distance19,596 km
Orbit Length:6.4 days
Surface Temperature:−220 °C

As one of the five moons of Pluto, the large moon Charon and Pluto are called a binary system. Charon is half as wide as Pluto, and is 750 mi/1,200 km in diameter.

It’s believed that both Pluto and Charon formed at the same time when there was a collision of two objects and the remaining debris probably created the other moons around Pluto.

Charon is tipped a bit to one side.Pluto has had a curious past.

Once considered to be our ninth planet, it was downsized to a dwarf planet. Pluto is so far away from Earth that we could only see blurred grey images.

When was Charon Discovered

Discovered in 1930, Charon wasn’t discovered until 1978 by James Christy, an astronomer at the Naval Observatory in Washington, D.C. Since he found it, Christy was allowed to name it.

At first he was going to name the moon for Charlene, his wife. He later made the decision to call the moon “Charon” to honor his wife, but make it sound more scientific.

After research, Christy found the name “Charon” that was the mythological ferryman that took the souls of those that had died across the river Styx to the underworld Many of his fellow astronomers wanted to continue the rule of naming the celestial bodies after Greek or Roman mythological creatures and some preferred the name Persephone.

Charon and Pluto are tidally locked, which means one side of Charon will always face Pluto and the other side is always turned away.

Charon orbit

Charon orbits Pluto every 6.4 Earth days, and that’s the same amount of time that it takes for Pluto to have one rotation.

The unusual rotation and orbit of Charon allowed scientists to observe that it entered a polar night in 1989 and then didn’t see the light of the sun until 2017.

Spacecraft Mission

The spacecraft mission New Horizons studied some of the landscape during this nighttime only because it received a small amount of light from Pluto.

Once New Horizons left the daytime side, Charon’s moonlight also assisted researchers in the study of Pluto. One of the surprising discoveries of the New Horizons mission was that Charon’ northern pole has a red formation.

The color comes from Pluto’s atmosphere that is constantly leaving due to the fact that it’s too small to hold on to most of its atmosphere.

The methane, nitrogen, and carbon monoxide leave Pluto’s surface and since Charon is so close, it captures some of this material.

Ultraviolet light

Ultraviolet light and galactic cosmic rays interact with the complex compounds of the material and through irradiation creates simple organic compounds.

Charon isn’t big enough to hold onto any atmosphere and the temperatures that Charon reach are extremely cold.

Charon’s polar temperatures range from -433 to -351 degrees F/-258 to -23 degrees C, which likely freezes the gas that reaches Charon without ever going through being liquid.

Facts about Charon

  • Charon’s surface is also made up of water-ice which gives it a gray-white color.
  • Charon has more craters than Pluto and this indicates that the surface may be older than Pluto.
  • Charon has only one mountain and it sits in a deep hole. It has been nicknamed “mountain in a moat.”
  • Charon’s weird mountain have geologists confused as they haven’t figured out how it was formed.
  • Charon has a huge canyon that reaches 1,000 mi/1,600 km across its surface.
  • Charon’s canyon is around four times longer than the Earth’s Grand Canyon and in some areas twice as deep.
  • The canyon makes the crust of Charon’s surface appear like it’s been split open.
  • South of Charon’s canyon lies the smooth plain called “Vulcan Planum.”
  • Faint ridges and grooves in the Vulcan Planum suggest that there may have been cold volcanic activity that’s called “cryovolcanism.”
  • Astronomers are talking about whether Charon could have once had an internal water ocean.


  • Pluto and Charon are called what kind of system?
    a binary system
  • In relation to the size of Pluto’s 5 moons, what place does Charon have?
  • What unique feature does the only moon on Charon have?
    a moon inside a hole
  • What does Charon’s huge canyon make Charon look like?
    the crust has been split open
  • What is the nickname of Charon’s mountain?
    mountain in a moat
  • What did the New Horizons mission discover at Charon’s north pole?
    a reddish color formation