IAU Circular 8577 announced on July 29, 2005 the discovery of three relatively bright Trans-Neptunian objects by M. E. Brown, C. A. Trujillo, and D. Rabinowitz using the Palomar 1.2-m Schmidt telescope. One of these objects, 2003 UB313, appears to be as big as or slightly bigger than the planet Pluto. The object's distance from the Sun varies between about 38 AU (1 AU is 150 million kilometers) and 98 AU, which is also close to its current distance. Its orbit has a period of about 560 years and is even more elongated and more inclined than the orbit of Pluto (let us here make a link to: http://www.gps.caltech.edu/~mbrown/planetlila/index.html).
We repeat below an earlier announcement of an IAU Working Group for establishing a definition of a planet. The discovery of 2003 UB313 has precipitated the need for such a definition in order to decide whether 2003 UB313 is to be classified as a planet or not. Until then the object will not be given an official name by the IAU.
The IAU notes the very rapid pace of discovery of bodies within the Solar system over the last decade, and so our understanding of the Trans-Neptunian Region is therefore still evolving very rapidly. This is in serious contrast to the situation when Pluto was discovered. As a consequence, the IAU has established a Working Group: "Definition of a Planete" under Division III, to consider the definition of a minimum size for a Planet. Until the report of this Working Group is received, all objects discovered at a distance greater than 40 AU will continue to be regarded as part of the Trans-Neptunian population.