Last week, I posted that an official definition of "planet" was being debated that would have expanded the number in our solar system to at least twelve. In the end though, the International Astronomical Union went with a much more conservative definition. Pluto has been demoted to a "dwarf planet, resulting in a decrease in the number of "classical" planets in our solar system to eight. From the Associated Press:
Much-maligned Pluto doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a … nearly round shape, and has cleared the neighborhood around its orbit."
Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.
Instead, it will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun — "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites.
