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

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).