Saturn's inner satellites : orbits, masses and the chaotic motion of Atlas from new Cassini imaging observations

Abstract

We present numerically-derived orbits and mass estimates for the inner Saturnian satellites, Atlas, Prometheus, Pandora, Janus and Epimetheus from a fit to 2580 new Cassini ISS astrometric observations spanning February 2004 to August 2013. The observations are provided in a supplementary table. We estimate GM_ Atlas=0.384+/-0.001 x 10^(-3)km^3s^(-2), a value 13% smaller than the previously published estimate but with an order of magnitude reduction in the uncertainty. We also find GM_ Prometheus=10.677+/-0.006x10(-3)km^3s^(-2), GM_Pandora=9.133+/-0.009x10^(-3)km^3s^(-2), GM_Janus=126.51+/-0.03x10^(-3)km^3s^(-2) and GM_Epimetheus=35.110+/-0.009x10^(-3)km^3s^(-2), consistent with previously published values, but also with significant reductions in uncertainties. We show that Atlas is currently librating in both the 54:53 co-rotation-eccentricity resonance (CER) and the 54:53 inner Lindblad (ILR) resonance with Prometheus, making it the latest example of a coupled CER-ILR system, in common with the Saturnian satellites Anthe, Aegaeon and Methone, and possibly Neptune's ring arcs. We further demonstrate that Atlas's orbit is chaotic, with a Lyapunov time of ~10 years, and show that its chaotic behaviour is a direct consequence of the coupled resonant interaction with Prometheus, rather than being an indirect effect of the known chaotic interaction between Prometheus and Pandora. We provide an updated analysis of the second-order resonant perturbations involving Prometheus, Pandora and Epimetheus based on the new observations, showing that these resonant arguments are librating only when Epimetheus is the innermost of the co-orbital pair, Janus and Epimetheus. We also find evidence that the known chaotic changes in the orbits of Prometheus and Pandora are not confined to times of apse anti-alignement.

arXiv comment23 pages, 16 figures. Accepted for publication in The Astronomical Journal 23 September 2014 (corrected Fig. 11)

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Cited by in corpus (12)

• From order to chaos in Earth satellite orbits
• What confines the rings of Saturn?
• Interior properties of the inner Saturnian moons from space astrometry data
• Origin of the chaotic motion of the Saturnian satellite Atlas
• Accretion of Ornamental Equatorial Ridges on Pan, Atlas and Daphnis
• Orbital Dynamics of Atlas (S XV): Its Current Orbit and the Recent Past
• A Librational Model for the Propeller Blériot in the Saturnian Ring System
• The main perturbing objects on the orbits of (616) Prometheus and (617) Pandora
• The current orbit of Atlas (SXV)
• Astrometric Reduction of Saturnian Satellites with Cassini-ISS Images Degraded by Trailed Stars
• Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn's Rings
• The dynamics of the outer edge of Saturn's A ring perturbed by the satellites Janus and Epimetheus