Siteadmin, Check users, Administrators
12,071
edits
Changes
Jump to navigation
Jump to search
Line 66:
Line 66: − +
→Problems for Uniformitarian Theory Posed by Ganymede
== Problems for Uniformitarian Theory Posed by Ganymede ==
== Problems for Uniformitarian Theory Posed by Ganymede ==
Ganymede is supposed to be a "geologically old" body because it is heavily cratered and because "new" terrain appears to overlay "old" terrain.<ref name=ambassador/> Yet the magnetic field persists--and at such a vast distance from the [[Sun]] (5.2 AU), the metal core ought to have cooled sufficiently for the field to die out.<ref name=Bland>Bland, M.T.; Showman, A. P.; Tobie, G. "[http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2020.pdf Ganymede's Orbital and Thermal Evolution and its Effect on Magnetic Field Generation]." ''Lunar and Planetary Science'', 38, March 2007. Accessed February 18, 2008.</ref> Astronomers have attempted to explain the persistence of the magnetic field by invoking tidal heating.
Ganymede is supposed to be a "geologically old" body because it is heavily cratered and because "new" terrain appears to overlay "old" terrain.<ref name=ambassador/> Furthermore, at such a vast distance from the [[Sun]] (5.2 AU), the metal core ought to have cooled sufficiently for the magnetic field to die out.<ref name=Bland>Bland, M.T.; Showman, A. P.; Tobie, G. "[http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2020.pdf Ganymede's Orbital and Thermal Evolution and its Effect on Magnetic Field Generation]." ''Lunar and Planetary Science'', 38, March 2007. Accessed February 18, 2008.</ref> Yet the field persists. Astronomers have attempted to explain the persistence of the magnetic field by invoking tidal heating. However, the [[Russell Humphreys]] model explains the field quite well. According to Humphreys, every celestial body begins with a magnetic field. The volume and conductivity of a celestial body's core, and not its temperature, determine the decay time of that field.<ref name=Humphreys/>
The 4:2:1 resonance among Ganymede, Europa, and Io presents another problem: the orbit of Ganymede ought not be quite as eccentric as it is. Explanations for this have not been universally satisfactory.
The 4:2:1 resonance among Ganymede, Europa, and Io presents another problem: the orbit of Ganymede ought not be quite as eccentric as it is. Explanations for this have not been universally satisfactory.