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Astronomers struggle to define 'planet'

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    Astronomers struggle to define 'planet'

    Astronomers struggle to define 'planet'

    LOS ANGELES - Our solar system is suffering an identity crisis. For decades, it has consisted of nine planets, even as scientists debated whether Pluto really belonged. Then the recent discovery of an object larger and farther away than Pluto threatened to throw this slice of the cosmos into chaos.

    Should this newly found icy rock known as "2003 UB313" become the 10th planet? Should Pluto be demoted? And what exactly is a planet, anyway?

    Ancient cultures regularly revised their answer to the last question and present-day scientists aren't much better off: There still is no universal definition of "planet."

    That all could soon change, and with it science textbooks around this planet.

    At a 12-day conference beginning Monday, scientists will conduct a galactic census of sorts. Among the possibilities at the meeting of the International Astronomical Union in the Czech Republic capital of Prague: Subtract Pluto or christen one more planet, and possibly dozens more.

    "It's time we have a definition," said Alan Stern, who heads the Colorado-based space science division of the Southwest Research Institute of San Antonio. "It's embarrassing to the public that we as astronomers don't have one."

    The debate intensified last summer when astronomer Michael Brown of the California Institute of Technology announced the discovery of a celestial object larger than Pluto. Like Pluto, it is a member of the Kuiper Belt, a mysterious disc-shaped zone beyond Neptune containing thousands of comets and planetary objects. (Brown nicknamed his find "Xena" after a warrior heroine in a cheesy TV series; pending a formal name, it remains 2003 UB313.)

    The Hubble Space Telescope measured the bright, rocky object at about 1,490 miles in diameter, roughly 70 miles longer than Pluto. At 9 billion miles from the sun, it is the farthest known object in the solar system.

    The discovery stoked the planet debate that had been simmering since Pluto was spotted in 1930.

    Some argue that if Pluto kept its crown, Xena should be the 10th planet by default — it is, after all, bigger. Purists maintain that there are only eight traditional planets, and insist Pluto and Xena are poseurs.

    "Life would be simpler if we went back to eight planets," said Brian Marsden, director of the astronomical union's Minor Planet Center in Cambridge, Mass.

    Still others suggest a compromise that would divide planets into categories based on composition, similar to the way stars and galaxies are classified. Jupiter could be labeled a "gas giant planet," while Pluto and Xena could be "ice dwarf planets."

    "Pluto is not worthy of being called just a plain planet," said Alan Boss, an astrophysicist at the Carnegie Institution in Washington, D.C. "But it's perfectly fine as an ice dwarf planet or a historical planet."

    The number of recognized planets in the solar system has seesawed based on new findings. Ceres was initially classified as a planet in the 1800s, but was demoted to an asteroid when similar objects were found nearby.

    Despite the lack of scientific consensus on what makes a planet, the current nine — and Xena — share common traits: They orbit the sun. Gravity is responsible for their round shape. And they were not formed by the same process that created stars.

    Brown, Xena's discoverer, admits to being "agnostic" about what the international conference decides. He said he could live with eight planets, but is against sticking with the status quo and would feel a little guilty if Xena gained planethood because of the controversy surrounding Pluto.

    "If UB313 is declared to be the 10th planet, I will always feel like it was a little bit of a fraud," Brown said.

    For years, Pluto's inclusion in the solar system has been controversial. Astronomers thought it was the same size as Earth, but later found it was smaller than Earth's moon. Pluto is also odd in other ways: With its elongated orbit and funky orbital plane, it acts more like other Kuiper Belt objects than traditional planets.

    Even so, Pluto remained No. 9 because it was the only known object in the Kuiper Belt at the time.

    When new observations in the 1990s confirmed that the Kuiper Belt was sprinkled with numerous bodies similar to Pluto, some scientists piped up. In 1999, the international union took the unusual step of releasing a public statement denying rumors that the ninth rock from the sun might be kicked out.

    That hasn't stopped groups from attacking Pluto's planethood. In 2001, the Hayden Planetarium at New York's American Museum of Natural History unleashed an uproar when it excluded Pluto as a planet in its solar system gallery.

    Earlier this year,
    NASA's New Horizons spacecraft began a 9 1/2-year journey to Pluto on a mission that scientists hope will reveal more about the oddball object.

    The trick for astronomers meeting in Prague is to set a criterion that makes sense scientifically. Should planets be grouped by location, size or another marker? If planets are defined by their size, should they be bigger than Pluto or another arbitrary size? The latter could expand the solar system to 23, 39 or even 53 planets.

    It's not an academic exercise — the public may not be open to a flood of new planets. Despite their differences, scientists agree any definition should be flexible enough to accommodate new discoveries.

    "Science progresses," said Boss of the Carnegie Institution. "Science is not something that's engraved on a steel tablet never to be changed."

    Bron: http://www.news.yahoo.com
    Last bewerkt door MoreLinux; 30-10-11, 13:20.
    Vuja De': the strange feeling you get that nothing has happened before.

    Pluto werd pas ontdekt werd na de voltooiing van de Planeten Suite van Holst. Achteraf gezien maar goed ook en sinds dit jaar gezien is er dus nooit iets mis geweest met de compleetheid van de suite. Ik kwam vandaag dit werkelijk hilarisch stukje tegen hierover, aangenomen dat de muziek en de achtergrond je een beetje ligt :-D

    Can you have a Planets suite without Pluto?

    David Ward

    Wednesday September 6, 2006 - The Guardian

    Pluto, actually a dwarf planet as reclassified by international astronomers.

    It is all very well 400 scientists voting to deprive Pluto of its planetary status. But a more perplexing conundrum remains: what happens now to the six-minute orchestral Pluto added to Gustav Holst's Planets suite barely six years ago? Will concert promoters lop off the final movement? Or will they, instead, simply list the eight-movement work as Holst's Seven Planets And A Dodgy Bit Of Rock Floating Quite A Few Miles Beyond Neptune Suite?

    Did those scientists think how Pluto's composer might feel about this astronomical demotion in his 60th birthday year? Did they cynically time their decision precisely to fit in with the release of a well-received new recording by the Berlin Philharmonic under Sir Simon Rattle?

    Colin Matthews, five of whose works have been included in Proms programmes this year to mark his bus-pass status, was the man commissioned by Manchester's Hallé orchestra to write the movement Holst had omitted from his suite, mainly because it was completed in 1917, 13 years before Pluto was discovered. The Hallé gave Pluto's first performance under Kent Nagano in the Bridgewater Hall, Manchester, in May 2000, when the piece emerged ethereally from the dying moments of Neptune as a fast scherzo: mainly quiet, apart from a couple of noisy outbursts. Everyone seemed happy and The Guardian called the piece "wonderfully imaginative".

    "It has had something like 100 performances," says Matthews. "It has been absolutely staggering. And I think there have now been four recordings. At the time I thought I might be pelted with rotten tomatoes, so I am very surprised by the way it took off.

    "There has been very little hostile reaction," says Matthews of his work, though he does confess that during a performance of his work at the Albert Hall during last year's Proms "the only two people who walked out were sitting in the two seats in front of me."

    But what happens to Pluto now? "I don't know", says Matthews. "It's not up to me any more. It will be interesting to see if there is any reaction. I might withdraw it from circulation and ban all future performances."

    That was probably a joke.

    The Hallé, rather than ordering Matthews to unwrite Pluto, will continue to play the piece. But they may be relieved that the International Astronomical Union not only decided to rescind Pluto's planetary status but refrain from creating four new planets too. For Rattle's new Berlin Philharmonic CD, he commissioned four pieces: Kaija Saariaho's Asteroid 4179 - Toutatis; Towards Osiris by Matthias Pintscher; Mark-Anthony Turnage's Ceres; and Brett Dean's Komarov's Fall. Said a Hallé spokesperson: "That would have blown the commissioning budget for the next three years".

    Kennelijk verkeren er nog meer groepen in de ontkenningsfase,
    "Zu groß, zu klein, Er könnte etwas größer sein..."