Pluto
Leading astronomers on Thursday approved historic new guidelines under which distant Pluto is no longer defined as a planet. After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union stripped Pluto of the planetary status it has held since its discovery in 1930. It is the first time that scientists have had a formal definition of what is — and is not — a planet. The decision by the prestigious international group spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club. For now, membership will be restricted to the eight "classical" planets in the solar system: Mercury,Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Much-maligned Pluto doesn’t make the grade under the new rules for a planet: "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 nearly round shape, and has cleared the neighbourhood around its orbit." Pluto is automatically disqualified because its oblong orbit overlaps with Neptune’s. Instead, Pluto will be re-classed in a new category of "dwarf planets", similar to what have been termed "minor planets". The definition also lays out third class of lesser objects orbit the sun —"small solar system bodies", a term that will apply to numerous asteroids, comets and other natural satellites. Two of the objects that at one point were cruising toward possible full-fledged planethood will join Pluto dwarfs: the asteroid Ceres, which was a planet in 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto nicknamed Xena by discoverer, Michael Brown of the California Institute of Technology.
posted by Vishal Chikhalikar @ 8:39 PM
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