…Neptune was discovered in 1846, and there seemed to be no more reason to worry. Then a guy named Clyde came along. In 1930 Clyde Tombaugh discovered a rocky body beyond the orbit of Neptune. Named Pluto late in March 1930, the planet was originally thought to have a mass similar to that of the Earth, but eventually more accurate estimate revised this to smaller and smaller amounts, until a mass of .2% of Earth’s was settled upon. Again, as with the “forgotten four”, Vesta, Juno, Ceres and Pallas, more and more bodies in Pluto’s region of space were found. Some of these bodies were given special names like Eris, Makemake, Haumea, Sedna, Chaos, Varuna, Quaoar and Typhon, among many other trans-Neptunian “planets”. In August 2006 the International Astronomical Union (IAU) put together a definition of a planet as an object that 1) orbits the sun, 2) has a nearly spherical shape and 3) has cleared its neighborhood of debris. The “demotion” of Pluto from planet to dwarf planet was simply the result of not having a formal definition of what a planet is. The five official dwarf planets are: Ceres, Pluto, Haumea, Makemake and Eris. Finally, nineteen moons are large enough to be classified as planets or dwarf planets, should they orbit the sun. They are: Ganymede, Titan, Callisto, Io, the Moon, Europa, Triton, Titania, Rhea, Oberon, Iapetus, Charon, Umbriel, Ariel, Dione, Tethys, Enceladus, Miranda and Proteus.
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