Bye bye Pluto

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Pluto, the ex-planet

This post is about the planet, not the cartoon’s character ;) .

From Science&Space on

Pluto no longer a planet, say astronomers. Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight. After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union (IAU) (not the eneby of BigG. :P ) stripped Pluto of the planetary status it has held since its discovery in 1930. ...
... 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 a ... nearly round shape, and has cleared the neighborhood around its orbit." Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's. Instead, it will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun -- "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites. ... The decision at a conference of 2,500 astronomers from 75 countries was a dramatic shift from just a week ago, when the group's leaders floated a proposal that would have reaffirmed Pluto's planetary status and made planets of its largest moon and two other objects. That plan proved highly unpopular, splitting astronomers into factions and triggering days of sometimes combative debate that led to Pluto's undoing. Now, two of the objects that at one point were cruising toward possible full-fledged planethood will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto whose discoverer, Michael Brown of the California Institute of Technology, has nicknamed "Xena." Charon, the largest of Pluto's three moons, is no longer under consideration for any special designation. Brown was pleased by the decision. He had argued that Pluto and similar bodies didn't deserve planet status, saying that would "take the magic out of the solar system." "UB313 is the largest dwarf planet. That's kind of cool," he said.

This revolution is only a unpopular decision for IAU: scientifically-speaking, there are very little changes. Definitions, not substances. Physical “features” of Pluto are the same. Also the position of the “semi-planet”, its orbit, its size, the composition of its atmosphere… etc. Differences for people? A 8 planet instead of 9 to remember in friend’s meetings and… goodbye to Disney Character with the name of a planet. Differences for young people? No matter, only a new geo-school-book (differences are only for parent’s money ;) ).

Sources: INAF-AstroNews,