Eight Planets and New Solar System Designations
How many planets are in the Solar System? This popular question now has a new
formal answer according the International Astronomical Union (IAU): eight.
Last week, the IAU voted on a new definition for planet and Pluto did not
make the cut. Rather, Pluto was re-classified as a dwarf planet and is
considered as a prototype for a new category of trans-Neptunian objects.
The eight planets now recognized by the IAU are: Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus, and Neptune. Solar System objects now
classified as dwarf planets are: Ceres, Pluto, and the currently
unnamed 2003 UB313. Planets, by the new IAU definition, must be in
orbit around the sun, be nearly spherical, and must have cleared the
neighborhood around their orbits. The demotion of Pluto to dwarf
planet status is a source of continuing dissent and controversy in
the astronomical community.