Dwarf planets Ceres, Pluto, and Eris. 插畫檔

In this image, from left to right, are the dwarf planets Ceres, Pluto, and Eris. Eris was discovered in 2003 and is now the largest of the known dwarf planets. It is believed to be slightly more massive than Pluto and follows a highly eccentric orbit that alternately brings it as close as the orbits of Neptune and Pluto and as far as over twice Pluto's furthest distance from the Sun. Pluto, a Kuiper object, was demoted to the status of dwarf planet in 2006 when the International Astronomical Union (IAU) reviewed Pluto's status in light of the recently discovered Eris, also a Kuiper object, but somewhat larger than Pluto. Pluto and Eris are also considered trans09/14/2009Neptunian objects, or trans09/14/2009Neptunian dwarf planets, because they orbit the Sun at a greater distance on average than Neptune.