  Natural satellite systems present a large variety of orbital configurations
in the solar system. While some are clearly the result of known processes,
others still have largely unexplained eccentricity and inclination values.
Iapetus has a still unexplained 3% orbital eccentricity and its orbital plane
is tilted with respect to its local Laplace plane. On the other hand,
astrometric measurements of saturnian moons have revealed high tidal migration
rates, corresponding to a quality factor Q of Saturn of around 1600 for the
mid-sized icy moons. We show how a past crossing of the 5:1 mean motion
resonance between Titan and Iapetus may be a plausible scenario to explain
Iapetus' orbit. We have carried out numerical simulations of the resonance
crossing using an N-Body code as well as using averaged equations of motion. A
large span of migration rates were explored for Titan and Iapetus was started
on its local Laplace plane with a circular orbit. The resonance crossing can
trigger a chaotic evolution of the eccentricity and the inclination of Iapetus.
The outcome of the resonance is highly dependent on the migration rate. For a
quality factor Q of over around 2000, the chaotic evolution of Iapetus in the
resonance leads in most cases to its ejection, while simulations with a quality
factor between 100 and 2000 show a departure from the resonance with
post-resonant eccentricities spanning from 0 up to 15%, and free inclinations
capable of reaching 11 degrees. Usually high inclinations come with high
eccentricities but some simulations show elements compatible with Iapetus'
current orbit. A quality factor between 100 and 2000 at the frequency of Titan
would bring Titan and Iapetus into a 5:1 resonance, which would perturb
Iapetus' eccentricity and inclination to values observed today. Such rapid
tidal migration would have avoided Iapetus' ejection around 40 to 800 million
years ago.
