An artist's view of the dwarf planet known as Eris

In July, 2005 astronomers announced the discovery of the largest object found in orbit around the Sun since the discovery of Neptune and its moon Triton in 1846. It is larger than Pluto, discovered in 1930. Like Pluto, the object is a member of the Kuiper belt, a swarm of icy bodies that orbit around the Sun beyond the orbit of Neptune.

In September 2006 it was officially named Eris. It was previously known as 2003 UB313 and by its nickname, "Xena".

In August, 2006 the International Astronomical ruled that Eris and Pluto are to be known as "dwarf planets."

The discovery was made using the Palomar Observatory's 48-inch Samuel Oschin Telescope by the team of Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale).

The discovery was made as a part of ongoing survey of the outer solar system using the Palomar QUEST camera and the Samuel Oschin Telescope at the Palomar Observatory. This survey has been operating since the fall of 2001, with the switch to the QUEST camera happening in the summer of 2003. To date the survey has turned up many bright Kuiper belt objects.

 To find objects, they take three pictures of a small region of the night sky over three hours and look for something that moves. The many billions of stars and galaxies visible in the sky appear stationary, while satellites, planets, asteroids, and comets appear to move. The process is descibed in more detail on this page.

Below is are the three discovery images.   

A diagram showing the relative sizes of Earth, Pluto, Eris and other distant solar system objects.

For more information and images visit Mike Brown's Eris Webpage.

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