 Observations of a stellar occultation by Eris in 2010 showed that its diameter was , very slightly less than Pluto, which was measured by "New Horizons" as in July 2015.Eris was discovered by the team of Mike Brown, Chad Trujillo, and David Rabinowitz on January 5, 2005, from images taken on October 21, 2003.The discovery was announced on July 29, 2005, the same day as and two days after , due in part to events that would later lead to controversy about Haumea.