Pluto was once considered to be one of the true planets within our solar system, however, due to the guidelines that define a planet, it was downgraded to a dwarf planet. Scientists new that even though Pluto is small, it has five moons, and Charon is the largest of these moons. Charon’s size is so great that astronomers refer to Pluto and Charon as a binary planet system.

Size comparisons: Earth, the Moon, and Charon

The entire moon system of Pluto is thought to have been created due to a collision early in the solar system’s history between Pluto and another object from the Kuiper Belt system. The crash created a lot of material that eventually came together into the satellites that we see orbiting Pluto. Scientists have observed that Pluto’s moons are “neatly nested” around Pluto.

Charon is around 50% of the size of Pluto and they are tidally locked so that the same surfaces always face each other.

Charon Statistics:

  • Orbits: Pluto-Charon Barycentre
  • Discovered By: James Christie
  • Discovery Date: June 22, 1978
  • Diameter: 1,207.2 km
  • Mass: 1.55 × 10^21 kg (2.1% Moon)
  • Orbital Period: 6.4 days
  • Orbit Distance: 17,536 km
  • Surface Temperature: – 220 degrees C


In June of 1978 James Christy and Robert Harrington were at the Flagstaff, Arizona U.S. Naval Observatory doing research to refine the orbit of Pluto around the sun. They weren’t looking for moons at all. James Christy became aware of some of the Pluto images that were oddly elongated and that there was a dot moving around Pluto in the same direction as the cycle of elongation. Christy searched through some of the earlier Pluto images and found the same elongation, and then realized that they had discovered the first known moon that was orbiting Pluto.


Christy decided on the name Charon, who was the ferryman of mythology who carried souls across the Acheron River also known as the River Styx. This was one of the five rivers in mythology in the underworld of Pluto. The name translates to “fierce brightness.” The choice of the name also coincided with the first four letters of his wife’s name, Charlene.

Formation, Structure and Surface:

The distance between Charon and Pluto is so close that they are called a double dwarf planet system. However, the distance from Earth is so great that until we sent spacecraft out to the far regions of space, Pluto remained a grey blur. The images from the Hubble Space Telescope did help a bit as it showed Pluto to have a bit of a red tinge to its color and Charon to be closer to a neutral grey. This indicated that the two have different compositions, surfaces, and structures.

The surface of Charon is affected by the atmosphere that Pluto sheds, giving some portions of the polar area a slight reddish color. The rest of the surface of Charon is mostly made up of water-ice and this gives it a gray-white color.


Charon ha a lot more craters than Pluto and this suggests that Charon’s surface is older than Pluto. Charon has only a one mountain and it’s nicknamed the “mountain in a moat,” because it is positioned in a deep hole. The mountain and the hole have stumped geologists because they have never seen anything like it.

Charon does have an incredible canyon named Vulcan Planum that is around 1,000 mi/1,600 km long over the surface. Its four times longer than the Grand Canyon in Arizona and in some places, it’s twice as deep. It appears to continue to wrap around the moon all the way to the dark side. The canyon gives the appearance that Charon’s crust has been split open. The surface around the canyon is smoother and less cratered than the northern areas of Charon. The ridges and grooves give a hint that the plain area may have had resurfacing due to cold volcanic activity that is called “cryptovolcanism.”

One theory developed by the team of the New Horizon spacecraft is that there might have been a subsurface ocean that had long ago frozen. The resulting change in volume could have created a crack that allowed water-based lavas to come to the surface.

The tidal-locked condition of Charon to Pluto combined with its orbit means that it doesn’t rise or set as our Earth moon does. Instead, Charon sits in the same place when viewed from Pluto’s surface. The dual pair are both tipped on their sides a bit in the same way that Uranus is tipped.

The Pluto-Charon binary system is the closest example that we have to study. Scientists think that they were both created at the same time due to a collision that involved a violent beginning.

In 1989 Charon’s South Pole entered a polar night and the sun won’t shine on that areas until 2107. The New Horizons spacecraft had the opportunity to study some of the landscape during the nighttime due to being illuminated by Pluto. Charon’s moonlight also assisted scientists to study Pluto when the spacecraft left the daytime side.

Atmosphere and Magnetosphere:

The New Horizons spacecraft got fairly close, showing that Charon had a red formation at its north pole. The red color is due to influence from the atmosphere from Pluto. The dwarf planet Pluto is too small to be able to hang onto any atmosphere for a length of time, so the methane, nitrogen, and carbon monoxide leaves the surface. Charon is so close that it captures some of it and funnels it to the surface. The material that is collected is affected by the sun’s ultraviolet light and the galactic cosmic rays so that complex compounds called tholins are created.

Charon isn’t big enough to hold onto any of the atmosphere that is shed by Pluto, and this makes the moon very cold. The polar temperatures range from -433 to -351 degrees F/-258 to -23 degrees C. Any gas that might reach Charon skips over the liquid phase and immediately freezes.

Charon doesn’t have a magnetosphere.

Could Life Exist?

Charon doesn’t have any of the requirements needed to begin and sustain life as we know it

Interesting Information:

  • The five moons of the Pluto system are: Charon, Nix, Hydra, Kerberos, and Styx.
  • Charon was large enough and had gravity strong enough to collapse and turn into a spherical shape, however the other 4 moons of Pluto are all oblong shaped.
  • Charon orbits Pluto in the same amount of time that it takes Pluto to make a complete rotation.
  • The original name of Charon was S/1978/P 1. This stands for the year discovered and that it was the first moon of Pluto.
  • We usually pronounce the moon as “SHAR-on,” however the Greek pronunciation is “CARE-on.”
  • Charon doesn’t really orbit Pluto, instead, both Pluto and Charon orbit a common center of gravity that is referred to as a “barycenter.” The barycenter is located just above the surface of Pluto.
  • Due to the odd orbit based on the barycenter, scientists have debated as to whether Charon should be considered a dwarf planet instead of one of the moons of Pluto.
  • A person weighing 100 lbs on Earth would weigh only 3 lbs on Charon.
  • A person weighing 100 lbs on Charon would weigh 503 lbs on Earth.
  • Charon’s surface seems to be made up of frozen water which is different from the frozen nitrogen, methane, and carbon dioxide of Pluto’s surface.
  • Astronomers think that Charon has an ice-based geology due to the active ice geysers (cryogeysers) and ice volcanoes (cryovolcanoes).
  • Before we know what the surface of Charon looked like, astronomers thought that it would be filled with craters. When they saw the images sent back from the New Horizons spacecraft they realized that Charon is covered in canyons, landslides, and variations in color.
  • The northern hemisphere of Charon has more craters than the southern hemisphere. This leads scientists to believe that the terrain of the north is older and that there is some kind of action taking place in the southern hemisphere to resurface the terrain there.
  • The dwarf planet Pluto is around one half of the width of the United States.
  • Charon is around half the size of Pluto, making it just a bit larger than the country of India.
  • It took the New Horizons spacecraft a bit under ten years to get to Charon and it was traveling at 50,000 mph.
  • Both Charon and Pluto complete their orbit around the sun once every 248 years.


In 2015, the New Horizons spacecraft flew within 17,000 miles of Charon. Thus far, it’s the only probe that has studied Charon.

Facts about Charon Moon for Kids:

  • If Charon wasn’t orbiting Pluto it would be considered to be a dwarf planet. Scientists are still discussing the classification of Charon so changes could occur in the future.
  • The surface of Charon is covered in nitrogen and methane ice.
  • Charon may have a rocky core.
  • Observations taken of Charon by the Gemini Observatory in Hawaii show that Charon may have ice-particle geysers as part of the process of cryovolcanism.
  • Astronomers are still unsure how Charon originated. There are a few theories including that Charon was created when an object from the Kuiper Belt collided with Pluto. Another theory is that in the early stages of Pluto’s formation, Pluto and Charon collided with each other but instead of breaking apart, they just began to orbit around each other.
  • The canyon on Charon is deep enough to fit Mount Everest in it.

Pop Culture:

The northern area of Charon is darker than any other location on the moon. It’s believed that the discoloration of the area is due to small particles that drift away from the atmosphere of Pluto. The team of the New Horizon spacecraft named this region “Mordor” after the area in J.R.R. Tolkien’s Lord of the Rings.

In the video game Mass Effect, Charon is a chunk of ice instead of a moon and it holds the technology from an ancient civilization that offers travel at faster-than-light speeds.

One of the chasms on Charon is quite impressive and is named Serenity Chasm after the ship on Joss Whedon’s cult classic television show Firefly. Serenity Chasm is 37 miles wide.

Some of the craters on Charon were named by the team of the New Horizons spacecraft. They named craters after their favorite characters from both Star Wars and Star Trek. They include Vader Crater, James T. Kirk Crater, Spock Crater, and Uhura Crater.

Most recently, additional names have been given to some of Charon’s craters and chasms that recognize other science fiction authors, characters and persons of notoriety. They include:

Butler Mons – in honor of Octavia E. Butler, the first science fiction author to win the MacArthur Fellowship and writer of the Patternist series and Xenogenesis trilogy.

Clarke Montes- acknowledging the scientist and science fiction author of many books and movies including 2001: A Space Odyssey.

Dorothy Crater- named for the beloved character and heroine, Dorothy, from L. Frank Baum’s Wizard of Oz series.

Kubrick Mons- film director of the renowned 2001: A Space Odyssey

Nemo Crater- Main character from Twenty Thousand Leagues Under the Sea and The Mysterious Island by Jules Verne.

Pirx Crater- the well-regarded science fiction writer Stanislaw Lem who wrote the main character of Pilot Pirx in the Tales of Pirx the Pilot.