Short answers, pulled from the story.
The team led by Mike Brown at Palomar Observatory announced the discovery of Eris on the 5th of January 2005. The object had actually been captured in images taken on the 21st of October 2003, but its slow motion across the sky caused automated software to discard it.
The International Astronomical Union accepted the name Eris on the 13th of September 2006. Before this decision, the public knew the object as Xena, an informal nickname inspired by the television series Xena: Warrior Princess.
The International Astronomical Union approved a new definition that reclassified both Eris and Pluto as dwarf planets on the 24th of August 2006. This decision reduced the number of known planets to eight, matching the count before Pluto's discovery in 1930.
Scientists calculated Eris to be 27% more massive than Pluto based on Dysnomia's orbital period of 15.774 days. Final results announced in October 2011 estimated its diameter at 2,326 kilometers, making Eris slightly smaller than Pluto but more massive.
Numerical integration by JPL Horizons shows that Eris reached perihelion around 1699 and will return on the 6th of December 2257. The object has an orbital period of 561 years with an aphelion of 97.7 astronomical units and a perihelion of 38.4 AU.