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Phaeton (or Phaëton, less often Phaethon) is the hypothetical planet posited to have existed between the orbits of Mars and Jupiter whose destruction supposedly led to the formation of the asteroid belt. The hypothetical planet was named for Phaëton, the son of the sun god Helios in Greek mythology, who attempted to drive his father's solar chariot for a day with disastrous results and was ultimately destroyed by Zeus. The asteroid 3200 Phaethon, sometimes incorrectly spelled Phaeton, shares Phaeton's name. 3200 Phaethon is a Mercury-, Venus-, Earth-, and Mars- orbit crossing Apollo asteroid with unusual properties. ==The Phaeton hypothesis== According to the discredited Titius–Bode law, a planet was believed to exist between Mars and Jupiter. Johann Elert Bode himself urged a search for the fifth planet. When Ceres, the largest of the asteroids in the asteroid belt (now considered a dwarf planet), was serendipitously discovered in 1801 by the Italian Giuseppe Piazzi and found to match the predicted position of the fifth planet, many believed it was the missing planet. However, in 1802 astronomer Heinrich Wilhelm Matthäus Olbers discovered and named another object in the same general orbit as Ceres, the asteroid Pallas. Olbers proposed that these new discoveries were the fragments of a disrupted planet that had formerly orbited the Sun. He also predicted that more of these pieces would be found. The discovery of the asteroid Juno by Karl Ludwig Harding and Vesta by Olbers buttressed the Olbers hypothesis. Theories regarding the formation of the asteroid belt from the destruction of a hypothetical fifth planet are today collectively referred to as the disruption theory. This theory states that there was once a major planetary member of the solar system circulating in the present gap between Mars and Jupiter, which was variously destroyed when: *it veered too close to Jupiter and was torn apart by its powerful gravity *it was struck by another large celestial body *it was destroyed by a hypothetical brown dwarf, the companion star to the Sun known as Nemesis *it was shattered by some internal catastrophe In the twentieth century, Russian comet specialist Sergei Orloff named the planet Phaeton after the story in Greek myth.〔La planète manquante(astrosurf.com)〕〔Les Astéroides(csdc.qc.ca)〕〔One of Our Planets is Missing (the galaxyexpress.com)〕〔One of Our Planets is Missing (lightforcenetwork.com)〕〔geocities(in Portuguese)〕 Today, the Phaeton hypothesis has been superseded by the accretion model.〔http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980810a.html〕 Most astronomers today believe that the asteroids in the main belt are remnants of the protoplanetary disk, and in this region the incorporation of protoplanetary remnants into the planets was prevented by large gravitational perturbations induced by Jupiter during the formative period of the solar system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phaeton (hypothetical planet)」の詳細全文を読む スポンサード リンク
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