  We revisit the dynamics of Prometheus and Pandora, two small moons flanking
Saturn's F ring. Departures of their orbits from freely precessing ellipses
result from mutual interactions via their 121:118 mean motion resonance.
Motions are chaotic because the resonance is split into four overlapping
components. Orbital longitudes were observed to drift away from Voyager
predictions, and a sudden jump in mean motions took place close to the time at
which the orbits' apses were antialigned in 2000. Numerical integrations
reproduce both the longitude drifts and the jumps. The latter have been
attributed to the greater strength of interactions near apse antialignment
(every 6.2 years), and it has been assumed that this drift-jump behavior will
continue indefinitely. We re-examine the dynamics by analogy with that of a
nearly adiabatic, parametric pendulum. In terms of this analogy, the current
value of the action of the satellite system is close to its maximum in the
chaotic zone. Consequently, at present, the two separatrix crossings per
precessional cycle occur close to apse antialignment. In this state libration
only occurs when the potential's amplitude is nearly maximal, and the 'jumps'
in mean motion arise during the short intervals of libration that separate long
stretches of circulation. Because chaotic systems explore the entire region of
phase space available to them, we expect that at other times the system would
be found in states of medium or low action. In a low action state it would
spend most of the time in libration, and separatrix crossings would occur near
apse alignment. We predict that transitions between these different states can
happen in as little as a decade. Therefore, it is incorrect to assume that
sudden changes in the orbits only happen near apse antialignment.
