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.