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Pinedale Online > News > August 2006 > Pluto demoted to ‘dwarf planet’
Pluto demoted to ‘dwarf planet’
Solar system officially back to 8 planets
August 28, 2006

One of the things we enjoy very much about Wyoming is our beautiful clear views of the stars in our night sky. Since so much of Wyoming is rural and without light pollution, we get to see the stars in brilliant clarity. It is a sky-watcher’s dream.

Here’s news from the people who are in charge of keeping track of all the celestial bodies and their appropriate nomenclature, the International Astronomical Union (IAU). The IAU met for their 26th General Assembly from August 14-25th in the city of Prague, capital of the Czech Republic. Last Thursday, members of the IAU voted to designate Pluto as a "dwarf planet". It has been considered our 9th planet since 1930 when it was discovered. Due to its great distance from the sun, and its elliptical orbit, there has been controversy about whether or not it is a true planet ever since it was discovered

The IAU members agreed that a "planet" is defined 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
(c) has cleared the neighborhood around its orbit.

The decision means that our Solar System now consists of eight "planets": Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

A new distinct class of objects called "dwarf planets" was also decided. It was agreed that "planets" and "dwarf planets" are two distinct classes of objects. The first members of the "dwarf planet" category are Ceres, Pluto and 2003 UB313 (temporary name). More "dwarf planets" are expected to be announced by the IAU 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. Two planet hopefuls, Ceres and Zena, were also given the official designation as dwarf planets by the IAU.

The IAU has been the arbiter of planetary and satellite nomenclature since its inception in 1919. The world's astronomers, under the auspices of the IAU, have had official deliberations on a new definition for the word "planet" for nearly two years. IAU formed a Planet Definition Committee (PDC), comprised by seven people who are astronomers, writers and historians with broad international representation, to research the matter. This group of seven convened in Paris in late June and early July 2006. They culminated the two year process by reaching a unanimous consensus for a proposed new definition of the word "planet."

The International Astronomical Union (IAU) was founded in 1919. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. Its individual members are professional astronomers all over the world, at the PhD level or beyond and active in professional research and education in astronomy. The IAU is composed of 8,858 individual members in 85 different countries worldwide.

Related Links:
International Astronomical Union
Science Daily Pluto Downgraded To 'Dwarf Planet' Status; Solar System Now Has Eight Planets

Pinedale Online > News > August 2006 > Pluto demoted to ‘dwarf planet’

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