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Mapping the Secular Resonance for Retrograde Irregular Satellites
Constructing dynamical maps from the filtered output of numerical
integrations, we analyze the structure of the secular resonance for
fictitious irregular satellites in retrograde orbits. This commensurability is
associated to the secular angle , where
is the longitude of pericenter of the satellite and
corresponds to the (fixed) planetocentric orbit of the Sun. Our study is
performed in the restricted three-body problem, where the satellites are
considered as massless particles around a massive planet and perturbed by the
Sun. Depending on the initial conditions, the resonance presents a diversity of
possible resonant modes, including librations of around zero (as found
for Sinope and Pasiphae) or 180 degrees, as well as asymmetric librations (e.g.
Narvi). Symmetric modes are present in all giant planets, although each regime
appears restricted to certain values of the satellite inclination. Asymmetric
solutions, on the other hand, seem absent around Neptune due to its almost
circular heliocentric orbit. Simulating the effects of a smooth orbital
migration on the satellite, we find that the resonance lock is preserved as
long as the induced change in semimajor axis is much slower compared to the
period of the resonant angle (adiabatic limit). However, the librational mode
may vary during the process, switching between symmetric and asymmetric
oscillations. Finally, we present a simple scaling transformation that allows
to estimate the resonant structure around any giant planet from the results
calculated around a single primary mass.Comment: 11 pages, 13 figure
A new perspective on the irregular satellites of Saturn - I Dynamical and collisional history
The dynamical features of the irregular satellites of the giant planets argue
against an in-situ formation and are strongly suggestive of a capture origin.
Since the last detailed investigations of their dynamics, the total number of
satellites have doubled, increasing from 50 to 109, and almost tripled in the
case of Saturn system. We have performed a new dynamical exploration of Saturn
system to test whether the larger sample of bodies could improve our
understanding of which dynamical features are primordial and which are the
outcome of the secular evolution of the system. We have performed detailed
N--Body simulations using the best orbital data available and analysed the
frequencies of motion to search for resonances and other possible perturbing
effects. We took advantage of the Hierarchical Jacobian Symplectic algorithm to
include in the dynamical model of the system also the gravitational effects of
the two outermost massive satellites, Titan and Iapetus. Our results suggest
that Saturn's irregular satellites have been significantly altered and shaped
by the gravitational perturbations of Jupiter, Titan, Iapetus and the Sun and
by the collisional sweeping effect of Phoebe. In particular, the effects on the
dynamical evolution of the system of the two massive satellites appear to be
non-negligible. Jupiter perturbs the satellites through its direct
gravitational pull and, indirectly, via the effects of the Great Inequality,
i.e. its almost resonance with Saturn. Finally, by using the Hierarchical
Clustering Method we found hints to the existence of collisional families and
compared them with the available observational data.Comment: 26 Pages, 27 Figures, 4 Table
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