Charon Moon

Charon Moon – Pluto Moons | The “Grand” Kid

Charon Moon – Basic Information

Billions of Miles Away

Moon Charon – The Big Boy with a Brown Cap

There are hundreds of moons within our tiny little solar system in this vast universe. Remember the days when human landed to our moon. And remember that was announced half a century ago! Distance from Earth to Moon is only 380.000 kilometers.

Well, this is mostly negligible in astronomical scales and incomparable considering our proximity to moon Charon.

In half a century, urge of exploration and tons of hours of hard work carried digital eyes to billions of miles away.

Isn’t it fantastic to have such clear images from 4 billion kilometers away?

Charon Moon
Best overview image of moon Charon by New Horizons Spacecraft. Source: NASA

What Is Charon?

Is Charon A Planet?

Charon planet? While Pluto is not a planet? Not that much!

Do you know how star systems are born? If you do, you are also aware of the fact that most of the residents within the star systems are formed as a result of their stars’ formation process. As well as other big objects in our Solar System, moon Charon has no privileges. She is a consequence of this chaotic birth too.

Charon is a Trans Neptunian round object. She is the biggest moon of Pluto, out of 5 moons in total. And similar to Pluto, she is wandering in Kuiper Belt most of the time.

Pluto and Charon
Pluto together with Charon, in almost true colors, floating in space. Source: NASA

One of the most interesting Charon-Pluto facts is, Charon also shares a mutually tidally locked motion with her parental planet. Considering the size and motional relation with Pluto, you might also hear some scientists call Pluto-Charon system a binary (double) planet system.

Scientific estimations reveal that Charon moon together with other Pluto moons were formed as a result of a collision between Pluto and another planet. It’s always hard to roll the time back, accurately estimate and make 100% sure how it exactly happened, however that’s the best scneario according to current formations.

Charon Moon – Orbit and Rotation

At least for couple of billions of years, this moon is destined to be by her mother planet’s side. Since Charon moon is 1/4 mass of Pluto and has a remarkable gravitational influence, the gravitational center of Pluto System is outside the lands of Pluto. Below figure explains how Charon orbits this gravitational center around Pluto.

Charon and Pluto Orbit
Pluto and Charon orbiting barycenter of Pluto System. Source: Wikimedia, Credit: Tomruen

Most of you guys must have heard the songs written about dark side of the moon. You might call it charming, but it’s not a proper definition. We, as senseless science fans, can better call that the “unapparent side”.

Our Earth completes one rotation on its own axis in about 24 hours, mumbling “let’s call it a day”. And the Moon fulfills one tour around the Earth in 27 days and 8 hours . Hereupon during the rotation, only one side of the Moon is facing the Earth. We call this fact tidal locking. Moon is tidally locked to the Earth.

However things are different in Pluto System: Both of them are tidally locked to each other. Which means, both Pluto and moon Charon face only one side of each other where the opposite hemispheres can never encounter.

Desperate couple of creatures in red outfit on Pluto and Charon. Source: NASA

Charon completes the orbit around the common gravitational center (barycenter) in 6.39 earth days. Obviously this period is the length of 1 Charon and Pluto day. While Charon has almost zero orbital eccentricity in regard to the barycenter, is seriously inclined to Pluto’s orbit (119.6°) and to the ecliptic (112.8°). The average distance between Pluto and Charon is 19.640 kilometers. This is almost 20 times closer than distance between the Earth and the Moon.

Todays Pluto and Charon: Future of Earth and Moon

Like it or not, the Pluto-Charon case illustrates the destiny of Earth and Moon. And quite a number of planets, moons and stars in common.

After millions of years, unfortunately Earth’s rotation on its own axis will substantially slow down (as it used to) up to some point. And this will deliberately balance the gravitational interaction with Moon. In other words, mutual tidal locking will happen. After that time, some of the world’s residents -who are not a big fan of travelling- can only dream about moonlight.

Let’s consider you were Charonian and have been living on the so called (by our Plutonian fellows) “dark side of Charon”. You’d probably be pretty surprised when you first saw something that big. And would probably worship her for thousands of years!

Charon and Pluto
Worth worshipping! Adorable image of Charon and Pluto on same frame. Source: NASA

Charon Moon – Size

Having a mass of 12% of Pluto, Charon has a radius of 606 kilometers. This is almost half of Pluto’s. By size, she is by far the biggest moon in the solar system comparing to her mother planet.

Pluto, Charon, Earth comparison
Size comparison of Pluto Charon and Earth. Source: NASA

Plutopic does and will always offer best service for understanding sizes of cosmic objects. Via our usual method, please gently slice moon Charon in half with a hypothetical huge knife. The inner surface area of the hemisphere will correspond to the surface area of South Africa.

Big knife
One of the Plutopic tools to cut moons into slices.

Charon Moon – Gravity and Surface Temperature

Certainly a good place to feel lighter. And certainly not easy to walk on! Although she is the biggest Pluto moon, Charon is incontestably small comparing to Earth. She has a surface gravity of 1/35 of Earth.

Another reason to challenge you when you go for a walk on this world will be the surface temperature. Average temperature on Charon surface is about -220°C. Evidently this is not surprising when you consider the average gap between Charon and the Sun.

Charon Moon Surface – Composition, Color and Other Features

Pluto’s surface consists mostly of nitrogen ice together with rare methane, carbon monoxide and water ice elements above its rocky core. However, no carbon monoxide or nitrogen exists on Charon. Based on surface analysis, Charon contains water ice to a large extent together with smaller amount of ammonia compounds. When it comes to methane, it is another story.

Charon surface
Close-up picture of moon Charon’s surface. Source: NASA

On the surface there are several different features like mountains, chasmas, craters and flat terrains. See details and names of surface features on following article: Charon map.

At first glance, you can see Charon is seperated from its equatorial area with a huge belt. While that belt is anticipated to be formed during tectonic activities in early years, it is unintentionally seperating the surface into two: A more rugged north area from the smoother south part.
According to researches, Charon has a geologically old and a more uniform surface especially when compared to Pluto. See more details about surface characteristics on Charon surface article.

Charon Moon – The Underground Ocean

Astronomers have brilliant methods to examine atmospheres of planets and moons. Same applies and supports evidence about surface materials. Those methods even work from observatories on or near Earth. However today’s methods do not reveal the secrets hidden beneath planetary surfaces. Even we don’t have sufficient tools yet to do that from only thousands of kilometers away, which was the proximity of New Horizons Spacecraft during its Pluto System flyby.

Charon ocean
Two different hypothesis about how Charon’s long frozen subsurface ocean might have effected the surface shaping. Source here, Credit: James Tuttle Keane, from Beyer et al. 2019

Although above is the case, scientists have strong evidences (including the above mentioned belt) that an underground ocean beyond Pluto surface can exist. Regarding Charon, another case is on the table: Researchers believe Charon too had an underground ocean. Not once, but twice! However those oceans are frozen in time and played an important role on satellite’s geological formation.

Approximately 55% of moon Charon consists of its rocky core. And it’s hard to say which materials it includes. However scientists believe the core is made of silicates.

The Unexpected Color Variation on North Pole

At first glance you can easily discriminate moon Charon from Pluto. The reason is not only the size, but also the colors. While grey is the dominant color on Charon, Pluto is dominated by brown and white.

Charon moon
Illustrated view of the north pole. Source:

OK, take a look again! You see the red/brown area on the north pole? This area is a proof that the mother has been feeding the baby with methane.

Astronomers believe that methane molecules sublimated from Pluto surface wanders all over the place. Consequently, those particles got caught by Charon gravity temporarily.

The temperature on the north pole of Charon is below freezing point of methane for over 100 years during Charon moon’s winter season. Therefore, those molecules are grabbed by Charon. Than firstly they freeze back to methane ice on surface. And similar to the process on Pluto surface, tholin layers arise following a bunch of chemical reactions. Eventually the methane ice evaporates and takes off from the surface while tholin layers remain.

So what we see there in red color are the tholin layers formed in last few million years.

Northern Hemispheres of Pluto and Charon
Northern Hemispheres of Pluto and Charon. Credit: Roman Tkachenko /NASA/ JHUAPL/SWRI

Atmosphere of Charon

Another dissimilarity between moon Charon and her parental planet is about atmosphere. There is no stable atmosphere covering above mentioned materials on Charon ground, however there is a proper Pluto atmosphere. This was estimated with observations in 1990‘s before New Horizons Mission and strongly verified afterwards.

Life on Moon Charon

One can get excited when water ice is detected on a rocky satellite’s surface. But creation of life in the way we know is more dependent on liquid water among with other factors. Above all, enough amount of heat and source of oxygen are also necessary for spreading life. However there are no such signs considering moon Charon’s current structure.

Moonlight view on Pluto
Illustration of moonlight view, as seen from Pluto surface. Source: JHUAPL / SwRI

This doesn’t mean that Charon did not host primitive life in the past and will not host in the future. But if she did or will, it will not be a long period till the harsh effects of radiation and low temperature sweep them off. Maybe it’s better to wait for a while and take another glance while our mighty sun becoming a red giant couple of billions years later.

In conclusion, it’s not the best time for now!

Discovery of Charon

James Christy, an astronomer working for U.S. Naval Observatory, had been working on Pluto’s orbit in 1970s. In short he and his team realized a periodical orbital disturbances which shouldn’t have happened without gravitational effect of another nearby object. Calendars were showing 22 June 1978 when this source of disturbance identified.

Than on 2nd July, the team decided to make one more observation for verification. All was in order! They located a small pale dot and officially announced discovery of Charon to the world on 7 July 1978. That was the first Pluto moon discovered ever.

James Christy - Charon discoverer
James Christy with the proof of Charon discovery. Source: NASA

Above glorious photo is taken on 22 June 2018, on the 40th anniversary of Charon’s discovery. Gentleman on the photo is Mr. James Christy, holding the first telescope images of Charon of his own.

Let’s admit we can not discriminate which one Charon is! Contradictorily, his desktop screen includes the high resolution image of Charon taken by New Horizons Spacecraft in 2015.

How Was Charon Named?

Together with the discovery, James Christy had another honor to offer moon Charon’s name to IAU.

And he did not only find a proper ancient Greek name. But also he is probably the unique person to honor his life partner with the moon he discovered. Her name is Charlene and he used to call her wife Char.

On 3 January 1986, the name was officially announced by IAU.

Surprisingly Charon is not “another god in Greek mythology”, but more of an ordinary (?) ferryman. His duty was to deal a strange boat which carries the corpses to the land of dead. Still sounds like a holy piece of work though!

38 years before Mr. Christy’s discovery, in science-fiction novel “Calling Captain Future” written in 1940 by Edmond Hamilton; names of three of the Pluto satellites were: Charon, Styx and Kerberos.

Goose flesh! Especially if you know the contemporary moon names in Pluto System. And obviously noone foreseen Nix and Hydra coming yet!

Calling Captain Future Novel
Science Fiction has always been an inspiration and fuel for science.

Charon in Astrology

Charon Moon, its size, distance to Earth, gravitational effect or any other specification.. Those have nothing to do with your horoscope, your daily life or anything else about your mood. This is common for any moon, planet or star you can think of.

Moon Charon did not have any influence on any human before and after 1978. At the end of the day, only influence Charon had was a new name in astrology. And maybe imaginary “houses” to accomodate!

Astrology means fairy tales.

Astronomy relies on facts; on a thing we named in last few centuries: The Science.



  • We aim to build a proper Pluto encyclopedia and your contributions are highly appreciated!
  • Any deficiencies on this article? Please type to below comment box or contact us from this link. We are ready to check and clarify.

Leave a Reply