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Pluto has been demoted to dwarf planet status

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.



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Im no astronomer
By lemonadesoda on 8/24/2006 6:51:09 PM , Rating: 2
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".


OK, I'm no astro-sherlock, but I can see some problems with these rules-of-definition. Two obvious ones are:

1./ What happens to a "double planet". In this case the "not cleared the neighbourhood around its orbit" rule applies, and it would be called a double dwarf planet. This is odd, since most double planets are HUGE

2./ Raw size or mass (absolute or relative) is not included. So a HUGE "planet" orbiting a star that happens to pass through some "uncleared" area would be called a "dwarf", whereas a solitary peanut orbiting a star that is "clear" would be called a planet.

I think it was a good idea to keep the definitional rules simple. But it seems that too simple can also be stupid




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