Recently it was announced that Pluto has a fifth moon orbiting around it. Known simply as P5, the moon is estimated to be anywhere between 10 to 25km across. It's leading more researchers to speculate that the collections of moons are results of a collision with another icy body out in the far flung Kuiper belt. The first known and largest moon, Charon, was discovered in 1978. Hubble found Nix and Hydra in 2006 then discovered P4 in 2011.Just to make it painfully clear, though it's odd how Pluto gained the moons, it is NOT a traditional planet. The classifications have nothing to do with moons. Venus has no moons, for example, but is a planet. Pluto is also not the largest Kuiper-based dwarf planet. The dwarf planet Eris, found in 2003, is actually larger than Pluto. There are other dwarf planets as well: Quaoar, Orcus, Sedna, 2005 FY9, the oddly shaped Haumea and Varuna, as well as a host of others. They all share the Kuiper region of space with Pluto.
What defines a planet comes down to some basic criteria:
- A planet is any object in orbit around the Sun with a diameter greater than 2000 km.
- A planet is any object in orbit around the Sun whose shape is stable due to its own gravity.
- A planet is any object in orbit around the Sun that is dominant in its immediate neighborhood.
Pluto, and many other dwarf planets, meet two of these requirements. What is lacking is clearing their neighborhood. This means basically there is a good deal of junk in their orbital path, they cross other orbiting objects and in a sense, behave closer to comets and asteroids. So while news of the new moon is neat, it does not change anything on how Pluto stands.