  We revisit the dynamics of Atlas. Using Cassini ISS astrometric observations
spanning February 2004 to August 2013, Cooper et al. (2015) found evidence that
Atlas is currently perturbed by both a 54:53 corotation eccentricity resonance
(CER) and a 54:53 Lindblad eccentricity resonance (LER) with Prometheus. They
demonstrated that the orbit of Atlas is chaotic, with a Lyapunov time of order
10 years, as a direct consequence of the coupled resonant interaction (CER/LER)
with Prometheus. Here we investigate the interactions between the two
resonances using the CoraLin analytical model (El Moutamid et al. 2014),
showing that the chaotic zone fills almost all the corotation sites occupied by
the satellite's orbit. Four 70:67 apse-type mean motion resonances with Pandora
are also overlapping, but these resonances have a much weaker effect. Frequency
analysis allows us to highlight the coupling between the 54:53 resonances, and
confirms that a simplified system including the perturbations due to Prometheus
and Saturn's oblateness only captures the essential features of the dynamics.
