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Shepherding of the Uranian Rings. II. Dynamics

Goldreich, Peter and Porco, Carolyn C. (1987) Shepherding of the Uranian Rings. II. Dynamics. Astronomical Journal, 93 (3). pp. 730-737. ISSN 0004-6256. https://resolver.caltech.edu/CaltechAUTHORS:20130313-085411501

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Abstract

We explore the dynamical significance of the orbital resonances, identified in Paper I (Porco and Goldreich 1987), involving the satellites 1986U7 and 1986U8, and the є, δ, and y rings. We demonstrate that these satellites are capable of exerting torques on the є ring which supply at the inner edge, and remove at the outer edge, the unperturbed angular-momentum luminosity transported by viscous stresses outward across the ring, provided that the ring has a mass which is comparable to the predicted value M_є = 6.1 X 10^(18) g, and that it is not more than a few meters thick. Thus there is no compelling reason to question the applicability of the standard theory of shepherding to the є ring. However, the standard theory does place rather stringent requirements on the ring's properties, suggesting that confinement might be due to the reduction of the angular-momentum luminosity by flux reversal. Flux reversal could be associated either with the ring's eccentricity gradient or with nonlinear density waves in its interior. The drag due to the planet's extended neutral hydrogen atmosphere probably has only a minor effect on the dynamics of the є, δ, and y rings. However, it poses a severe problem for the shepherding of the ɑ and β rings unless their masses have been seriously underestimated. This problem, and the large s-band optical depths of these rings, lead us to question the proposal that self-gravity is responsible for enforcing rigid precession in narrow rings.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1086/114355DOIUNSPECIFIED
http://adsabs.harvard.edu/abs/1987AJ.....93..730GADSUNSPECIFIED
Additional Information:© 1987 American Astronomical Society. Received 7 October 1986; revised 18 November 1986. We thank Dr. Scott Tremaine for fruitful discussions and for the hospitality extended to us by him and the staff at the Canadian Institute for Theoretical Astrophysics at the University of Toronto, where part of this research was conducted. This work was supported under JPL Contract No.954057, NASA grant NGL-05-002-003, and NSF grant AST-8313725.
Funders:
Funding AgencyGrant Number
JPL954057
NASANGL-05-002-003
NSFAST-8313725
Subject Keywords:URANUS, RINGS, SHEPHERD SATELLITES, DYNAMICS, TORQUE, 1986U7, 1986U8, EPSILON RING, DELTA RING, GAMMA RING, PHYSICAL PROPERTIES, LUMINOSITY, ANGULAR MOMENTUM, FLUX, ECCENTRICITY, DENSITY WAVES, ATMOSPHERE, DRAG, ALPHA RING, BETA RING, OPTICAL PROPERTIES, DEPTH, GRAVITY EFFECTS, THEORETICAL STUDIES, MASS, CALCULATIONS
Issue or Number:3
Record Number:CaltechAUTHORS:20130313-085411501
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130313-085411501
Official Citation:Shepherding of the Uranian Rings. II. Dynamics Goldreich, P. & Porco, C. C. Astronomical Journal v.93, p.730-737
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37486
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:13 Mar 2013 16:32
Last Modified:03 Oct 2019 04:48

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