Discovered in 2002, Quaoar, of which the diameter is 1,250 kilometres, was at the time the largest object in the solar system discovered since Pluto in 1930. Since then even larger objects have been discovered: (90482) Orcus, (90377) Sedna and finally (136199) Eris in 2005.
It is on a circular trajectory at about 6.3 billion kilometres from the Sun and 1.8 billion kilometres from Neptune.
The discovery by Michael Brown and Chadwick Trujillo, of Caltech (Pasadena, United States), tends to confirm the theory that in the Kuiper belt there are objects of a size comparable to that of Pluto. This strengthens the position of astronomers who classify Pluto as a Kuiper belt object, the largest to date, and not a planet.
Pluto follows an elliptical trajectory that takes it inside Neptune's orbit and beyond that of Quaoar. Half ice and half rock, Quaoar "is black, dirty ice" says Brown. It has been blackened by ultraviolet light which has gradually transformed its organic compounds since the beginning of the solar system, the objects in the Kuiper belt being the remains of planet formation.