What Exactly Is a Dwarf Planet?

On January 5, 2005, American astronomer Michael E. Brown (of CalTech, Princeton, and Berkeley) with fellow astronomers David L. Rabinowitz (Yale University and University of Arizona) and Chad Trujillo (University of Hawaii, Gemini Observatory and Northern Arizona University) were given credit for their discovery of a planetoid they called Eris, at the time, the largest dwarf planet known in the Solar System.  The astronomical team actually discovered Eris in 2003, but its (relatively) small size and distance from Earth required rigid documentation for the discovery to be accepted.  Eris is larger than Pluto, the dwarf planet that used to be considered just a “planet” from its discovery in 1930 until the discovery of Eris and other heavenly bodies in our solar system beyond the orbit of Neptune.  With the discovery of Eris and other objects orbiting the Sun at distances beyond Neptune, Pluto was “downgraded” from a planet to a dwarf planet along with Eris and other such objects.