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Dwarf Planet Pluto

Why does Pluto have 3 moons and Earth only 1?


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February 27, 2009 7:38PM

The system of Pluto-Charon is similar to our Earth-Moon system, with Charon (Pluto's large moon) rotating the dwarf planet and having one face always toward Pluto. However, Charon is almost half Pluto's size. This means that the center of gravity for the pair is outside Pluto's surface, and the two actually co-rotate. Pluto's other two moons, Hydra and Nix, are likely captured asteroids. The closest thing to another for Earth is one of the many Sun-orbiting asteroids that cross our orbit. Named "Cruithne", it is smaller than Hydra and Nix, but has too high a relative velocity in its own orbit to be captured by Earth.