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Nick Cooper, Stefan Renner Carl Murray Encelade Meeting, UPMC, 22 January 2014 Recent Results on the Dynamics of Atlas

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Charnoz et al. (2010)

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Astrometric Data 2580 Cassini ISS observations of Atlas, Prometheus, Pandora, Janus, Epimetheus QM SATELLORB and F Ring Images Data span Feb 2004 to Aug 2013 Atlas observations mostly centroided UCAC2 for pointing correction Phase correction SATELLORB astrometry by Mike Evans

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Numerical Model Integration of full equations of motion in 3D Perturbations from 8 major satellites, Sun, Jupiter Saturn’s oblateness up to J6 Runge-Kutta-Nystrom 12 th order integrator Variational equations integrated simultaneously, iteratively fitting to observations Solving for states and masses of Atlas, Prometheus, Pandora, Janus and Epimetheus at epoch

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Pre-fit (SAT353)Post-fit O-C Residuals

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O-C Post-fit Residuals

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Mean longitudes vs. time Resonant arguments vs. time ILR CER

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Full Numerical Model Atlas, Prometheus, Saturn only Atlas Geometrical Elements

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FLI vs time Full Numerical Model 3-body Numerical Model (Atlas, Prometheus, Saturn)

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(Starting Conditions from Numerical Fit) Coralin Surfaces of Section ATLAS a_mean=137665.39 km

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Coralin Surfaces of Section (Starting Conditions from 3-body Model) ATLAS a_mean=137665.39 km

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Summary Fit to new astrometry: significant reduction in O-C residuals. Order of Magnitude improvement in mass estimates. Atlas dynamics dominated 54:53 resonance with Prometheus. Another example of coupled ILR/CER motion! Regular and chaotic episodes (FLI analysis). Chaos is due to Prometheus only. Atlas, Prometheus dynamics can be modelled as a 3-body system (CORALIN).

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