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Gravitational evidence for an undifferentiated Callisto

Anderson, J. D. and Lau, E. L. and Sjogren, W. L. and Schubert, G. and Moore, W. B. (1997) Gravitational evidence for an undifferentiated Callisto. Nature, 387 (6630). pp. 264-266. ISSN 0028-0836. doi:10.1038/387264a0.

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Before the arrival of the Galileo spacecraft at Jupiter, models for the interior structure of the four galilean satellites-lo, Europa, Ganymede and Callisto-ranged from uniform mixtures of rock and ice (that is, undifferentiated objects) or rocky cores surrounded by a mantle of water ice. Now it appears that lo has a large metallic core and that Ganymede is strongly differentiated, most probably into a three-layer structure consisting of a metallic core, a silicate mantle and a deep outer layer of ice. Direct information on the interior structure of Callisto determined from previous spacecraft fly-bys was essentially limited to an estimate of the mean density being intermediate between pure ice and pure rock. Here we report measurements of Callisto's gravitational field which reveal that, in contrast to lo and Ganymede, this galilean satellite is most probably a homogeneous object consisting of a solar mixture of 40% compressed ice and 60% rock (including iron and iron sulphide). Callisto's undifferentiated state is consistent with the apparent lack of an intrinsic magnetic field, and indicates that the outermost galilean satellite has not experienced a heating phase sufficiently high to separate its rock and metal components from the lighter ices.

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Additional Information:© 1997 Macmillan Publishers Limited. Received 12 December 1996; accepted 9 April 1997. This work was sponsored by the Galileo Project and was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. G.S. and W.B.M. were supported by NASA through the Galileo Project at JPL and the Planetary Geology and Geophysics Program.
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Issue or Number:6630
Record Number:CaltechAUTHORS:20150617-085823375
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58307
Deposited By: Tony Diaz
Deposited On:17 Jun 2015 16:14
Last Modified:10 Nov 2021 22:02

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