What Defines a Planet?
What constitutes a planet? The International Astronomical Union (IAU) developed some definitions in 2001, modified them again in 2003, and as of August 24, 2006, the IAU has come up with another definition. The IAU said in a statement that the definition for a planet is now officially known as "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 neighborhood around its orbit."
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 neighborhood around its orbit, and (d) is not a satellite.
All other objects except satellites orbiting the sun shall be referred to collectively as "Small Solar-System Bodies".
According to the IAU, more dwarf planets are expected to be announced in the coming months and years. Currently, a dozen candidate dwarf planets are listed on IAU's dwarf planet watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better-known.
According to Paul Hertz, Chief Scientist for the Science Mission Directorate at NASA Headquarters, NASA will use the new guidelines established by the International Astronomical Union, and continue pursuing exploration of the most scientifically interesting objects in the solar system, regardless of how they are categorized.
A dwarf planet is a category of celestial bodies defined in a resolution passed by the International Astronomical Union (IAU) on August 24, 2006.
Currently, there are three celestial bodies that have been redefined by the IAU as dwarf planets:
- UB313 (informally known as Xena, and now formally known as Eris)
By: Zookeeper - 2007-10-05 17:57:29