Pluto and Charon; Twin Dwarf Planets

Above Image: Artist’s impression of how the surface of Pluto might look, according to one of the two models that a team of astronomers has developed to account for the observed properties of Pluto’s atmosphere, as studied with CRIRES. Charon is shown as the large body on the left side of the sky with the Sun as the bright star on the right. Credit: ESO/L. Calçada

Pluto has been a touchy subject since it was booted from the League of Planets (a fictional group that I created just now for this article) by Mike Brown in 2006 and reclassified as a dwarf planet. This post, however, is going to take neither side of that argument. Before I get started on what I want to focus on in this article, I want to provide a little info about the Pluto System, as a whole, before delving into the microcosm of the Pluto/Charon relationship.

Pluto System: There are a total of 6 major celestial bodies that comprise the Pluto system, with Pluto being the focal point. The other five consist of Pluto’s moons, (from closest to furthest) Charon (1978), P5 (2012),   Nix (2005), P4 (2011) and Hydra (2005). It is also theorized that Pluto may have a weak ring system, but due to its distance from Earth, it is very difficult to confirm this theory. We will find out for sure when the New Horizons spacecraft arrives at the Pluto System in 2015.


I want to focus on the dance of “the twin planets,” as Pluto and Charon used to be referred to after Charon’s discovery, but prior to the discovery of Nix and Hydra. Charon is actually the largest moon in the entire solar system, when compared proportionately to the planet (or, in this case, dwarf planet) that it orbits. Charon is fully half the size of Pluto! That being the case, Pluto and Charon actually orbit each other. Every planet with moons has a center of gravitational mass that is shares with any given moon in its system. This point is known as “the barycenter“. Since the mass of any celestial body is measured from the center of that object, most of the barycenter’s in our solar system are actually located below the surface of the planet involved in the system. As an example, The Earth/Moon Barycenter is actually located 1062 miles below the surface of the Earth on a straight line trajectory between the absolute center of the Earth and the Moon. I said earlier that most of the barycenters in our solar system were this way, that actual number is all of them… except three. The Pluto/Charon Barycenter is located outside of the body of Pluto, as shown at the beginning of the following animation.


Since the barycenter is actually located outside of the body of Pluto, there is a strong argument that Charon is not actually a moon of Pluto, but that Pluto and Charon are actually a binary planet system. I would agree with this assessment, as, considering the previously mentioned information, both Pluto and Charon orbit a point in space between the two objects, and it is actually that point, the barycenter, that is in orbit around the sun. Therefore, if Pluto is considered a dwarf planet by current astronomical ruling, the same applies to Charon.

This is all based on information that is pretty lacking, considering the potential of the things we have yet to learn about the Plutonian system. I plan to re-visit the subject after the New Horizons spacecraft arrives in the Plutonian System in July 2015.

As a side note, Jonathan Coulton wrote a song called “You’re My Moon” about the Pluto/Charon relationship back in 2006 after Pluto was officially declared no longer a planet. Check it out!



About Alloy Matt

Happy Husband | Beardsman | Blogger | Dreamer | Wholigan | Drinker of Coffees | Tweeter of Hashtags | Gamer of Table Tops | Amature Astronomer | Fanboy of Apple

Posted on August 20, 2012, in Geek, Nerd, Science, Space and tagged , , , , , , , , , , , , . Bookmark the permalink. 1 Comment.

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