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Astronomy: Pluto the ex-planet
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Just like with the discovery of Uranus the existence of Pluto was suggested before the planet was discovered. William Pickering and Percival Lowell analyzed distortions in Uranus' orbit and predicted a planet six times heavier than Earth. The search for the proposed planet began in 1905 at the Mount Wilson Observatory and at the Lowell's Observatory. After the death of Lowell, his brother financed a telescope for the Lowell's Observatory. In 1929 the young astronomer Clyde W. Tombaugh searched photographic plates from this telescope and on 18 February 1930 discovered Pluto. With a diameter of 2390 kilometers the icy planet is smaller than Earth and too far from Neptune to account for the calculated distortions. The calculated prediction of a large planet was wrong. The moon CharonIn 1978 James Christy of the US Navel Observatory discovered Pluto's moon Charon. This satellite is about 1190 kilometers in diameter, half the size of Pluto. The two objects are so close together that they are locked and alway face the same side.Many astronomers think of Pluto and Charon as double planets. AtmosphereIn the early 1980s methane gas was observed on Pluto and Charon, while they were nearing their closest approach to the Sun. The heating during Pluto's 248-year orbit varies by more than 60%, in the moving away the methane gas forms white methane ice on the surface.Also nitrogen and carbon monoxide may be present in the atmospheres of these twin. ResearchSo far Pluto is the only planet not to be photographed in high resolution. The last stop of the Voyager 2 spacecraft was Pluto's neighbour Neptune.But, in 2015 the spacecraft New Horizons is sceduled to arrive at Pluto. Today's pictures from the Hubble Space Telescope only distinguish vague surface markings. Pluto was a planet (1930-2006)Although in 1930 no-one doubted that Pluto was a new planet, today we look back somehow differently. With the knowledge in mind of the Edgeworth-Kuiper Belt, and different similar sized bodies discovered, Pluto is no longer considered a planet as of 2006 (ruling of the International Astronomical Union, 24 August 2006).Pluto is now classified by IAU as a Trans-Neptunian Object, an iceberg similar to hundreds other icebergs with a diameter of 1000 kilometers. Especially after a claim of the discovery of Planet X in 2005, the IAU was forced to define clearly what a planet is. Pluto and Charon are comparable to Neptune's moon Triton - a suspected former member of the Edgeworth-Kuiper Belt - and Quaoar (2002 LM60) discovered on 4 June 2002. Pluto has the diameter of an ice body, the orbit in the Kuiper Belt and the excentric orbit like other ice bodies in the Kuiper Belt. Related subjects>> Spacecraft New Horizons (estimated to arrive at Pluto in 2015)>> Edgeworth-Kuiper Belt >> Quaoar (2002 LM60) >> Neptune's moon Triton |
 Picture of Pluto in true color  Picture of Pluto and its only moon Charon |
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