Explanation:
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.
