|
.〕 | rotation = Synchronous〔 | axial_tilt = 0.1° | albedo = 0.67 ± 0.03 | magnitude = 5.29 (opposition)〔 | temperatures = yes | temp_name1 = Surface | min_temp_1 = ≈ 50 K〔 | mean_temp_1 = 102 K (−171.15°C) | max_temp_1 = 125 K | atmosphere = yes | surface_pressure = 0.1 µPa (10−12 bar) }} Europa 〔, or as (ギリシア語:Ευρώπη)〕 (Jupiter II), is the sixth-closest moon of Jupiter, and the smallest of its four Galilean satellites, but still the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei〔 and was named after Europa, mother of king Minos of Crete, who became one of Zeus' lovers. Progressively better observations of Europa have occurred over the centuries by Earth-bound telescopes, and by space probe flybys starting in the 1970s. Slightly smaller than the Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, whereas craters are relatively rare. It has the smoothest surface of any known solid object in the Solar System.〔(Europa Moon | Planets.org.uk )〕 The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life. This hypothesis proposes that heat from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics. On 8 September 2014, NASA reported finding evidence supporting earlier suggestions of plate tectonics in Europa's thick ice shell—the first sign of such geological activity on a world other than Earth. On 12 May 2015, scientists announced that sea salt from a subsurface ocean may be coating some geological features on Europa, suggesting that the ocean is interacting with the seafloor. This may be important in determining if Europa could be habitable for life. In December 2013, NASA reported the detection of "clay-like minerals" (specifically, phyllosilicates) on the icy crust of Europa.〔 In addition, the Hubble Space Telescope detected water vapor plumes similar to those observed on Saturn's moon Enceladus, which are thought to be caused by erupting cryogeysers. The ''Galileo'' mission, launched in 1989, provided the bulk of current data on Europa. No spacecraft has yet landed on Europa, but its intriguing characteristics have led to several ambitious exploration proposals. The European Space Agency's Jupiter Icy Moon Explorer (JUICE) is a mission to Europa that is due to launch in 2022. NASA's planned Europa Multiple-Flyby Mission mission will be launched in the mid-2020s. ==Discovery and naming== Europa, along with Jupiter's three other large moons, Io, Ganymede, and Callisto, was discovered by Galileo Galilei on 8 January 1610,〔 and possibly independently by Simon Marius. The first reported observation of Io and Europa was made by Galileo Galilei on 7 January 1610 using a 20×-magnification refracting telescope at the University of Padua. However, in that observation, Galileo could not separate Io and Europa due to the low magnification of his telescope, so that the two were recorded as a single point of light. Io and Europa were seen for the first time as separate bodies during Galileo's observations of the Jupiter system the following day, 8 January 1610 (used as the discovery date for Europa by the IAU). Europa is named after Europa, daughter of the king of Tyre, a Phoenician noblewoman in Greek mythology. Like all the Galilean satellites, Europa is named after a lover of Zeus, the Greek counterpart of Jupiter. Europa was courted by Zeus and became the queen of Crete. The naming scheme was suggested by Simon Marius, who discovered the four satellites independently.〔 Marius attributed the proposal to Johannes Kepler.〔Marius, S.; (1614) ''Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici'' (), where he (attributes the suggestion ) to Johannes Kepler〕 The names fell out of favor for a considerable time and were not revived in general use until the mid-20th century. In much of the earlier astronomical literature, Europa is simply referred to by its Roman numeral designation as ' (a system also introduced by Galileo) or as the "second satellite of Jupiter". In 1892, the discovery of Amalthea, whose orbit lay closer to Jupiter than those of the Galilean moons, pushed Europa to the third position. The ''Voyager'' probes discovered three more inner satellites in 1979, so Europa is now considered Jupiter's sixth satellite, though it is still sometimes referred to as .〔 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「Europa (moon)」の詳細全文を読む スポンサード リンク
|