August 24, 2006
Pluto stripped of its status as a planet
By Alan Crosby
PRAGUE (Reuters) - Pluto was stripped of its status as a
planet on Thursday when astronomers from around the world
redefined it as a "dwarf planet," leaving just eight classical
planets in the solar system.
the ninth planet, and furthest from the sun, in the solar
However, the definition of a planet approved after a heated
debate among some 2,500 scientists from the International
Astronomical Union (IAU) meeting in Prague drew a clear
distinction between Pluto and the other eight planets.
The scientists agreed that to be called a planet, a
celestial body must be in orbit around a star while not itself
being a star.
It also must be large enough in mass for its own gravity to
pull it into a nearly spherical shape and have cleared the
neighbourhood around its orbit.
Pluto was disqualified because its oblong orbit overlaps
The new definition -- the first time the IAU has tried to
define scientifically what a planet is -- means a second
category called "dwarf planets," has been created, as well as a
third category for all other objects, except satellites, known
as small solar system bodies.
The need to define what it takes to be a planet was driven
by technological advances that enable astronomers to look
further into space and to measure more precisely the size of
celestial bodies in our solar system.
From now on, traditional planets will be restricted to
eight: Mercury, Earth, Jupiter, Saturn, Neptune, Venus, Mars