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Rotation and the internal structures of the major planets and their inner satellitesMeasurements of the rotational periods coupled with those of the masses, the mean radii, and the shapes or the gravitational moments (J2 and J4) enable important constraints to be placed on the internal structures of some remote bodies. Values of J2 for Uranus and Neptune have been calculated from the observed precession rates of the narrow eccentric and inclined Uranian rings and of the orbit of Triton, Neptune's massive satellite. Recent observations of the motions of spots have yielded reliable rotational periods for these planets. These observations are used to show that Uranus and Neptune may have quite different internal structures. The shapes of satellites that are close to their primaries may yield information on the degree of internal differentiation of these bodies. Io, Mimas, Enceladus, and Miranda are of interest in this respect. Residuals in the observed precession rates of the Uranian rings, about 0.005 deg/day, that cannot be accounted for by the best-fit model of J2 and J4 may be related directly to observed irregular variations in ring width of magnitude over 2 km and may indicate the existence of shepherding satellites with mass ratios of over 10 to the -10th. If this is the case, then the effects of these satellites on the precession rates of the rings will result in an appreciable uncertainty in the value of J4 for Uranus.
Document ID
19850036736
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Dermott, S. F.
(Cornell University Ithaca, NY, United States)
Date Acquired
August 12, 2013
Publication Date
November 27, 1984
Publication Information
Publication: Philosophical Transactions, Series A
Volume: 313
Issue: 1524
ISSN: 0080-4614
Subject Category
Lunar And Planetary Exploration
Accession Number
85A18887
Funding Number(s)
CONTRACT_GRANT: NAGW-392
Distribution Limits
Public
Copyright
Other

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