dozen or ten to be redefined
Planets to be redefined
Mon, 21 Aug 2006, 09:49:00
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WITH the recent discovery of three new planets - larger than the smallest and furthest away Pluto - a new definition of the word 'planet' has been suggested by the world's leading astronomers as they are preparing to reshape our understanding of the solar system in a galactic big bang. For decades children around the world have been taught that there are nine planets in the solar system - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. But there have been suggestions that Pluto now no longer merits its place on the list with the new discovery of larger asteroids.
The International Astronomical Union (IAU) and the president of its 'Planet Definition Committee', Iwan Williams, have come forward with the suggestion of redefining 'planet' underlining the importance of 'a need to rationalise, a need to say where we are' as around 200,000 asteroids have already been identified in the vast visible universe so far. The IAU is proposing a new definition that would distinguish planets from what it calls 'small solar system bodies' - comets and asteroids that orbit the sun - and divide them into categories. According to IAU astronomers, those discovered before 1900 AD would be called simply 'planets' while a new sub-category of 'plutons' would be introduced as a compromise between those who want to banish Pluto from the planetary club and those who want its status maintained.
The astronomers and experts who are going to attend the IAU's 26th general assembly to be held in Prague by the end of this week, would debate on whether to include a dozen other planetary candidates including Vesta, Pallas and Hygea and any new discoveries. The IAU's Resolution-V relating to definition has already been presented to astronomers in this regard for initiating debate and discussion before any conclusion that is to be reached through voting. If the new definition is adopted, there will be eight planets, few dozen plutons and tens of thousands of small solar system bodies. The move, as a whole, would result in three 'pluton' planets being created along with Pluto: Pluto's moon, Charon, Ceres, an asteroid that for several decades after its discovery was described as a planet, and the so-called 'object 2003 UB313', which was discovered in 2003 by an US astronomer and goes by the unofficial name of 'Xena'.
As efforts are on in all possible ways to know and find more and more things that are in existence in the vast universe - yet to be explored, it would be humanly difficult to draw any final conclusion at a given time. With the passing of days, new and more discoveries would be made to enrich knowledge as the human urge in this regard continues irresistibly to know the unknown.
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■「惑星１２個」幻に？ 国際天文学連合で異論続出(読売新聞 - 08月21日 23:41)