Exotic Eris

Known for a brief time as the “tenth planet,” Eris is our Solar System’s the largest and most distant known dwarf planet, a new class of objects created in response to its discovery. Learn more about this unusual object:

• Eris was discovered on January 5, 2005, by astronomers Mike Brown, Chad Trujillo, and David Rabinowitz. It had been captured in a series of photographs taken more than a year earlier, on October 21, 2003, as part of a systematic scan of the outer Solar System in search of planetary bodies. The team announced their discovery on July 29, 2005. Because Eris is slightly larger than Pluto, its existence led, in part, to Pluto’s reclassification as a dwarf planet.

• Eris is located in the region of space beyond the planet Neptune, known as the scattered disc. It is currently about 97 Astronomical Units from the Sun, though its highly eccentric orbit brings it within 36 AUs at its closest. One AU is equal to the distance between the Earth and the Sun – about 92,957,000 miles!

• Eris has an eccentric, or oval-shaped, orbit. It takes the dwarf planet 557 years to orbit the Sun, and about eight hours to rotate once on its axis.

• The surface of Eris is believed to be somewhat similar to Pluto’s, comprised mainly of rock and methane ice.

• Eris is believed to be about 1,441 miles in diameter. It is slightly larger than Pluto in size, and 27% more massive. It is about a quarter the size of the Earth.

• Eris is named for the Greek goddess of strife and discord. The name is apropos in light of the dispute the object’s discovery caused in the astronomical community over the definition of a planet. Because it could not be officially named until after it was classified, Eris was known as Xena for more than a year, after the television heroine.

• Eris has one known moon, Dysnomia, named for the daughter of the Greek goddess Eris.

• Temperatures on Eris range between -405° F and -358° F.

• Because of its small size, Eris has only a very thin atmosphere. Ice on its surface sublimates directly into water vapor and escapes into space.

• Eris, like most dwarf planets, can only be seen through very high-powered telescopes.