New draft definition of a planet
19 August 2006
by Carina Lee
After extensive debate, refining, and two years of study, researchers from the International Astronomical Union (IAU) have come up with the definition of a planet. The definition is necessary to draw the line between planets and smaller solar bodies which may exist beyond what has already been discovered. The definition, which is up for the approval at the IAU General Assembly, will currently include 12 planets in our Solar System plus 3 objects known as plutons (planets with orbits of more than 200 years). The 12 planets will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, and 2003 UB313.
It is difficult to draw a fine line between what can be classed as a planet, a pluton, or just an accumulation of solar material floating around in Space. This proposed definition is based upon the two constraints of orbit and size. To satisfy this definition, a planet must orbit around a star, while not being a star itself, and must meet the size and mass requirements of being above 800km and 5 x 1020kg. President of the IAU, Ron Ekers, rationalises this new definition, by explaining “Modern science provides much more knowledge than the simple fact that objects orbiting the Sun appear to move with respect to the background of fixed stars. For example, recent new discoveries have been made of objects in the outer regions of our Solar System that have sizes comparable to and larger than Pluto. These discoveries have rightfully called into question whether or not they should be considered as new ‘planets’.” The consequences of this new definition would not only have an impact on the astronomy branches of science, but would also have cultural repercussions as well as implications for future discoveries. Like the idea of whether we are going to limit the number of planets in our Solar System, or keeping adding them on as new celestial bodies are discovered. |
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