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55 Cancri c (abbreviated 55 Cnc c) is an extrasolar planet in an eccentric orbit around the Sun-like star 55 Cancri A, making one revolution every 44.34 days. It is the third known planet in order of distance from its star. 55 Cancri c was discovered on June 13, 2002 and has a mass roughly half of Saturn. The planet and its host star is one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).〔(NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars ). IAU.org. 9 July 2014〕〔(NameExoWorlds ).〕 The process involves public nomination and voting for the new names, and the IAU plans to announce the new names in mid-November 2015.〔(NameExoWorlds ).〕 ==Discovery== Like the majority of known extrasolar planets, 55 Cancri c was detected by observing changes in its star's radial velocity. This was achieved by making sensitive measurements of the Doppler shift of the star's spectrum. At the time of discovery, 55 Cancri A was already known to possess one planet (55 Cancri b); however, there was still a drift in the radial velocity measurements which was unaccounted for. In 2002, further measurements revealed the presence of a long-period planet in an orbit at around 5 AU from the star. Even when both of the two planets were accounted for, there was still a periodicity at around 43 days. However, this period is close to the rotation period of 55 Cancri A, which led to the possibility that the 43-day period was caused by stellar rotation rather than a planet. Both the 43-day planet (designated 55 Cancri c) and the 5 AU planet (designated 55 Cancri d) were announced in the same paper, labeled in order of increasing distance from the star. Further measurements which led to the discovery of the inner planet 55 Cancri e in 2004 lent support to the planet hypothesis. Photometric measurements of the star over 11 years show no activity with the same period as 55 Cancri c's radial velocity variations, and furthermore the period is stable over long timescales, which is inconsistent with the hypothesis of stellar activity causing the radial velocity variations. The amplitude of the radial velocity signal is inconsistent with stellar variations on stars with 55 Cancri A's low level of chromospheric activity.〔 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「55 Cancri c」の詳細全文を読む スポンサード リンク
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