Not everyone agrees on whether Pluto is a planet or a dwarf planet. But no one is arguing that he is an interesting and unusual being. Everything this object does, from the fact that it is sometimes closer to the Sun than Neptune, means something different.
Interesting features of this distant dwarf planet include its moons and orbits around Pluto. More precisely, they are notable for not orbiting Pluto. These moons are surprisingly orbiting a point outside of Pluto, which appears to be because of its largest moon, Charon.
Charon is about half the size of Pluto and about one-eighth its mass. This moon is so large that the system’s center of gravity – the point around which objects orbiting a system – actually orbits, about 83 percent of the dwarf planet’s radius, really away from Pluto’s surface, 960 kilometers away.
Also, Jupiter doesn’t technically orbit the Sun, but orbits a point just outside its surface, about 7 percent of the Sun’s radius, which is understandable given its size and distance from the Sun.
At the International Astronomical Union meeting in 2006, when the category of “dwarf planet” was created and Pluto was reclassified, a proposal came to begin calling Pluto and Charon double planets. This proposal was not accepted, but some now refer to this pair as double dwarf planets.
There are four other moons worth noting: Stix, Nix, Kerberos, and Hydra. All four of them are small and irregularly shaped. The orbital planes appear to be consistent with Pluto’s equator, and scientists believe they are the result of a collision between Pluto and a similar-sized object.
The orbits of these four small worlds are very close to circular and do not have Pluto at their centers. Instead, they orbit around their center of gravity at some point between Pluto and Charon. This intricate and bizarre dance causes almost perfect patterns in their orbits. The cycles of Styx, Nix, Kerberos and Hydra have a 3:4:5:6 pattern with Charon’s. This means that for every 60 cycles of Charon, Styx has 20, Nix has 15, Kerberos has 12 and Hydra has 10.
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