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An Aug. 24 vote of the International Astronomical Union resulted a new
definition of the term “planet,” for which the solar system object
known as Pluto does not qualify. This reduces the total number of
planets in our solar system to eight.
An Aug. 24 vote of the International Astronomical Union resulted a new definition of the term “planet,” for which the solar system object known as Pluto does not qualify. This reduces the total number of planets in our solar system to eight.
The new definition categorizes the solar system’s bodies as either planets, dwarf planets, or small solar system bodies. Pluto is now considered a dwarf planet.
The new definition for a 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.
It is this last requirement that eliminated Pluto, as well as recently discovered objects Ceres, Sedna and 2003 UB313.
Only about 5 percent of the world’s professional astronomers were present for the vote, and there has been some dissent in the larger astronomical community.
“This definition stinks, for technical reasons,” said Alan Stern, leader of NASA’s New Horizons mission to Pluto, in a recent space.com interview. “It’s patently clear that Earth’s zone is not cleared. Jupiter has 50,000 trojan asteroids. It won’t stand. It’s a farce.”
Other terms that the IAU considered in place of “dwarf planet”: plutons, plutoids, plutonids, plutonoids, plutinos, Tombaugh Objects, Tombaugh Planets and plutians, according to Robert Roy Britt on www.livescience.com.
Currently a dozen candidate “dwarf planets” are listed on the IAU’s “dwarf planet” watchlist, according to an IAU release.
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