spacetoday.net: Astronomers demote Pluto

Posted: Thu, Aug 24, 2006, 9:17 PM ET (0117 GMT)
Pluto moons illustration (STScI)

Astronomers voted Thursday on a formal definition of the term "planet" that will leave the solar system with only eight such bodies, having relegated the former planet Pluto to a lesser category. Astronomers meeting at the International Astronomical Union conference in Prague approved a resolution Thursday that defines a planet as an object orbiting the Sun large enough to be "nearly round" and also having cleared the "neighborhood" around it. Objects that orbit the Sun and are round but have not cleared their neighborhood of other objects would instead be classified as "dwarf planets". The decision leaves the solar system with eight "classical" planets but demotes Pluto to the status of swarf planet, where it will be joined by several other objects. The decision is a sharp turnaround from just a week earlier, when astronomers put forth a proposal that would increase the number of planets to 12, and possibly more, by not including the neighborhood-clearing provision.