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Mercury's magnetic field is approximately a magnetic dipole (meaning the field has only two magnetic poles) that is significant, and apparently global, on planet Mercury. Data from ''Mariner 10'' led to its discovery in 1974; the spacecraft measured the field's strength as 1.1% that of Earth's magnetic field. The origin of the magnetic field can be explained by dynamo theory, and because the magnetic field is strong enough near the bow shock, it slows down the solar wind, which induces a magnetosphere. ==Strength== The magnetic field is about 1.1% as strong as Earth's.〔 At the Hermean equator, the relative strength of the magnetic field is around 300 nT. Although much weaker than Earth's magnetic field (about 1/100 its magnitude) according to ''Mariner 10'' data, the magnetic field is still strong enough to deflect solar wind emissions, inducing a magnetosphere. Because Mercury's magnetic field is weak while the interplanetary magnetic field it interacts with in its orbit (a perihelion at 0.307 AU and an aphelion at 0.467 AU) is relatively strong, the solar wind dynamic pressure at Mercury′s orbit on the average is also a factor of three larger than that at Earth, for example. Mercury's magnetic field being weaker than Earth's may be because its core had cooled and solidified more quickly than the Earth. Scientists have detected Mercury's magnetic field to be weaker than Jupiter's moon Ganymede's. Whether the magnetic field changed to any significant degree between the ''Mariner 10'' mission and the ''MESSENGER'' mission remains an open question. A 1988 J.E.P. Connerney and N.F. Ness review of the Mariner magnetic data noted eight different papers in which were offered no less than fifteen different mathematical models of the magnetic field derived from spherical harmonic analysis of the two close ''Mariner 10'' flybys, with reported centered magnetic dipole moments ranging from 136 to 350 nT-RM3 (nT is nanoteslas, RM is a Mercury radius of 2436 km). In addition they pointed out "()stimates of the dipole obtained from bow shock and/or magnetopause positions (only) range from approximately 200 nT-RM3 (Russell 1977) to approximately 400 nT-RM3 (Slavin and Holzer 1979b)." They concluded that "the lack of agreement among models is due to fundamental limitations imposed by the spatial distribution of available observations." 〔 〕 Anderson ''et al.'' 2011, using high-quality ''MESSENGER'' data from many orbits around Mercury – as opposed to just a few high-speed flybys – found that the dipole moment is 195 (unicode:±) 10 nT-RM3.〔 〕 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「Mercury's magnetic field」の詳細全文を読む スポンサード リンク
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