Sedna, or 2003
VB12, was the first of the new Kuiper Belt objects to be discovered.
Xena and others followed.
Xena, or UB 313, discovered in January 2005,
was the first of these new objects to exceed Pluto's diameter, which
further pushed the ongoing debate amongst astronomers as to the
exact nature of a planet. The recent re-classification of the solar
system, which more clearly defined a planet as 'rounded by its own
gravity', thereby disqualifying large asteroids, was announced by
the International Astronomer's Union, the IAU, in Summer 2006.
This re-classification demoted Pluto and
promoted Ceres, which lies between Mars and Jupiter, in the asteroid
belt, to the class of minor planets.