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).