Dwarf Planet: History of Astronomy

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Today is the anniversary of the discovery, on 5 Jan 2005 by astronomers Michael E. Brown, Chadwick A. Trujillo and David L. Rabinowitz, of the dwarf planet Eris, a trans-Neptunian object with a diameter of around 2,325 kilometres (1,445 miles) and which orbits the Sun once every 557 years. Eris lies at an average distance from the Sun equal to around 1.72 times that of Pluto and has one known moon, Dysnomia, seen here just to the left of Eris on an image taken with the Hubble Space Telescope in 2007. Eris is notable in that it has been found to have a mass greater than Pluto, eventually leading to Pluto's demotion from planet status in August 2006, when the International Astronomical Union (IAU) downgraded Pluto to a ‘dwarf planet’.

 

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