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OGLE-2005-BLG-390Lb is a 'super-Earth' extrasolar planet orbiting the star OGLE-2005-BLG-390L, which is situated 21,500 ± 3,300 light years away from Earth, near the center of the Milky Way galaxy. On January 25, 2006, Probing Lensing Anomalies NETwork/Robotic Telescope Network (PLANET/Robonet), Optical Gravitational Lensing Experiment (OGLE), and Microlensing Observations in Astrophysics (MOA) made a joint announcement of the discovery. The planet does not appear to meet conditions presumed necessary to support life. == Physical characteristics == OGLE-2005-BLG-390Lb orbits its star at an average distance of 2.0 to 4.1 AU, or an orbit that would fall between the orbits of Mars and Jupiter in the Solar System. (This range of distances is the range of error in measurement and calculation; it does not represent the planet's orbital eccentricity, as its orbital elements are not known.) Until this discovery, no small exoplanet had been found farther than 0.15 AUs from a main-sequence star. The planet takes approximately 10 Earth years to orbit its star, OGLE-2005-BLG-390L.〔 OGLE-2005-BLG-390Lb's sun (located in the constellation Scorpius, RA 17:54:19.2, Dec −30°22′38″, J2000, 6.6 ± 1.0 kpc distance)〔 is thought to likely be a cool red dwarf (95% probability), or a white dwarf (4% probability), with a ''very'' slight chance that it is a neutron star or black hole (<1% probability). Regardless of the star's classification, its radiant energy output would be significantly less than that of the Sun. The planet is estimated to be about five times Earth's mass (5.5 ''M''E). Some astronomers have speculated that it may have a rocky core like Earth, with a thin atmosphere. Its distance from the star, and the star's relatively low temperature, means that the planet's likely surface temperature is around . If it is a rocky world, this temperature would make it likely that the surface would be made of frozen volatiles, substances which would be liquids or gases on Earth: water, ammonia, methane and nitrogen would all be frozen solid. If it is ''not'' a rocky planet, it would more closely resemble an icy gas planet like Uranus, although much smaller.〔.〕 The planet is not so much notable for its size, or possible composition — although these are unusual — but for the fact that such a relatively small exoplanet was detected at such a relatively large distance from its star. Prior to this, "small" exoplanets, such as Gliese 876 d which has a "year" of less than 2 Earth-days, were detected very close to their stars. OGLE-2005-BLG-390Lb shows a combination of size and orbit which would not make it out of place in Earth's own solar system. "The team has discovered the most Earthlike planet yet," said Michael Turner, assistant director for the mathematical and physical sciences directorate at the National Science Foundation, which supported the work. At 5.5 Earth masses, the planet was less massive than the previous candidate for lowest-mass extrasolar planet around a main-sequence star, the 7.5 Earth mass Gliese 876 d. Since 2013, many Earth-sized or smaller planets around main-sequence stars have been detected by the ''Kepler'' spacecraft and others. 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「OGLE-2005-BLG-390Lb」の詳細全文を読む スポンサード リンク
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