1735    Mathematical calculations suggest that it is on this day that dwarf planet Pluto moved inside the orbit of Neptune for the last time before 1979.

2003    Images of the dwarf planet Eris are taken and subsequently used in its discovery by the team of Michael E. Brown, Chad Trujillo, and David L. Rabinowitz.

2005    Eris, the largest known dwarf planet in the solar system, is discovered by the team of Michael E. Brown, Chad Trujillo, and David L. Rabinowitz using images originally taken on October 21, 2003, at the Palomar Observatory.

2006    The International Astronomical Union (IAU) redefines the term "planet" such that Pluto is now considered a Dwarf Planet.