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Ganymede and CallistoIt is noted that even though the two moons have very similar masses and densities and formed in the same part of the solar system, Ganymede underwent widespread geologic activity whereas Callisto appears to have remained dormant. It is believed that the reason for this may involve several factors. Callisto has undoubtedly experienced at least some internal differentiation; if, however, the differentiation was less complete than for Ganymede or if it took place more slowly, some expansion could have occurred without the crust ever having been fractured. All the major heat sources in these moons produce more heat in Ganymede than in Callisto. Since Ganymede is more massive and dense than Callisto, its silicate content is significantly higher. Because the major radioactive elements are present only in the silicates, radiogenic heating is greater for Ganymede than for Callisto (by an estimated 60%) Ganymede has also undergone significantly more accretional heating than Callisto, not only because of its greater mass and stronger gravitational attraction, which lead to higher impact velocities, but also because it lies closer to Jupiter. The strong gravitational attraction of Jupiter greatly increases the impact velocities of any debris coming from outside the Jupiter system.
Document ID
19830041556
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Squyres, S. W.
(NASA Ames Research Center Theoretical and Planetary Studies Branch, Moffett Field, CA, United States)
Date Acquired
August 11, 2013
Publication Date
February 1, 1983
Publication Information
Publication: American Scientist
Volume: 71
Subject Category
Lunar And Planetary Exploration
Accession Number
83A22774
Distribution Limits
Public
Copyright
Other

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