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Nick Cooper, Stefan Renner Carl Murray
Encelade Meeting, UPMC, 22 January 2014
Recent Results on the Dynamics of Atlas
Charnoz et al. (2010)
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
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 12th order integrator
• Variational equations integrated simultaneously, iteratively fitting to observations
• Solving for states and masses of Atlas, Prometheus, Pandora, Janus and Epimetheus at epoch
Pre-fit (SAT353) Post-fitO-C Residuals
O-C Post-fit Residuals
Mean longitudes vs. time
Resonant arguments vs. time
ILR
CER
Full Numerical Model Atlas, Prometheus, Saturnonly
Atlas Geometrical Elements
FLI vs time
Full Numerical Model 3-body Numerical Model(Atlas, Prometheus, Saturn)
(Starting Conditions from Numerical Fit)Coralin Surfaces of Section
ATLAS a_mean=137665.39 km
Coralin Surfaces of Section(Starting Conditions from 3-body Model)
ATLAS a_mean=137665.39 km
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).