Definition of "planet"

The definition of "planet" has for some time been the subject of intense debate. Despite the term having existed for thousands of years, no definition of "planet" by an official body of scientists existed before the early 21st century. Until the beginning of the 1990s, there was little need for a definition, as astronomers had only a single sample within the solar system to work from, and the sample was small enough for its many irregularities to be dealt with individually.However, after 1992 and the discovery of the myriad tiny worlds beyond the orbit of Neptune, the size of the sample rose from nine to at least several dozen. Following the further discovery of the first extrasolar planet beyond our solar system in 1995, the number of samples has reached hundreds. These new discoveries not only increased the number of potential planets, but, in their variety and peculiarity challenged long perceived notions of what a planet could be.The issue of a clear definition for planet came to a head in 2005 with the discovery of the trans-Neptunian object Eris, a body larger than the smallest accepted planet, Pluto. In response, the International Astronomical Union, which is internationally recognized by astronomers as the body responsible for resolving issues of astronomical nomenclature, released its decision on the matter. According to their definition, a planet is a body that orbits the Sun, is large enough for its own gravity to make it round, and has "cleared the neighbourhood" of smaller objects.