DailyTech reported last week that
Pluto was coming close to being dismissed as an official planet of our solar
system. Pluto, which was first discovered in 1930, has been the subject of
debate for astronomers for over 70 years. The International Astronomical
Union's 2,500 astronomers (representing 75 countries) gathered to decide the
fate of Pluto and the results are in.
The International Astronomical Union (IAU) voted to demote Pluto from the
ranks of the solar system's now 8 planets. The decision comes as Pluto no
longer fits the newly ratified definition of a planet decided upon by the IAU
this week. The new definition states that a planet is “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 does not clear the neighborhood around its orbit
because its orbit overlaps with its much larger neighbor Neptune. This
therefore disqualifies it from planet status according to the IAU. Instead,
Pluto will be classified as a dwarf planet and join the ranks of other dwarf
planets such as Ceres, which lies between Mars and Jupiter and 2003 UB313 or
‘Xena’ as discoverer Michael Brown of the California Institute of Technology
has nicknamed it. ‘Xena’ is an icy object that lies after Pluto and is slightly
larger than the now dwarf planet.
quote: The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:
(1) A classical planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".