 In 2006, the first measurement of the volume of Eris erroneously (until the "New Horizons" mission to Pluto) showed it to be slightly larger than Pluto, and so was thought to be equally deserving of the status of 'planet'.Because new planets are discovered infrequently, the IAU did not have any machinery for their definition and naming.After the discovery of Sedna, it set up a 19-member committee in 2005, with the British astronomer Iwan Williams in the chair, to consider the definition of a planet.