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Written by spacetravel.org
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Thursday, 22 September 2005 22:46 |
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A 19-member working group, which was assembled by the International Astronomical Union, has still not been able to agree on a definition of planet. The working group was assembled 18 months ago, when a large new body called Sedna was found in the outer solar system. In July 2005, a large object, 2003 UB313, was discovered in the Kuiper belt beyond Neptune. Its discovers called it a planet because it is larger than Pluto.
Some astronomers say that the definition of a planet should be based on size. This means that the number of planets in the Solar System would increase, as there are other Pluto-sized Kuiper Belt objects that would then qualify as planets.
Others say that a planet should be the dominant body in its immediate neighbourhood, based on the dynamics of its orbit and its size relative to its neighbours. This would mean Pluto is not a planet, because it crosses the orbit of Neptune, which is a larger body.
Still others suggest using qualifying adjectives to clarify what is meant when the term planet is used, for example, calling Pluto a historic planet.
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