Pluto no longer a planet
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.
The new definition makes little sense to me. What does "clear the neighborhood around its orbit" mean exactly? How does the overlap between Pluto's orbit and Neptune's disqualify "automatically" Pluto but not Neptune? I suspect there is some sloppy journalism going around here, and that the official resolution must be clearer.
Language Log's comment is:
The International Astronomical Union has spoken, and Pluto is no longer to be called a "planet." It is, however, still considered a "dwarf planet." Don't be fooled by any preconceptions you might have about English hyponymy: a dwarf planet is not, in fact, a planet.