  Gas giant planets in the Solar system host large satellite systems with
multiple regular and irregular moons. Regular moons revolve around their host
planet in circular, low inclination short period orbits, and are thought to
form in-situ through coagulation processes. In contrast, irregular moons have
highly inclined (and even retrograde), typically eccentric and long period
orbits around their host planet. Irregular moons are therefore often thought to
be unbound objects in helio-centric orbits that were later captured to their
current orbits around the planet. Here we study the a different possibility in
which regular moons form in-situ, and dynamically evolve through mutual
moon-moon scattering. We find that such evolution can excite the satellites
into high eccentricities and inclinations. We find that moons are either
ejected from the host planet to become runaway moons, or stay bound and become
prograde orbiting irregular moons with inclined and eccentric orbits around
their host planet. Ejected moons, unbound to the planet, can later be
temporarily re-captured by the host planet even at retrograde orbits. Such
moons are eventually re-ejected from the system or collide with the planet, at
least in the absence of dissipative processes (e.g. collisions with existing
bound moons, a debris disk or through tidal interactions with the host planet),
not currently modeled. Uncaptured runaway moons may eventually be ejected from
the Solar system, or be captured into stable helio-centric orbits and
contribute to the populations of asteroidal or trans-Neptunian objects. Such
scenarios are potentially relevant both for the gas-giant satellites in the
Solar system and for the dynamical evolution of exomoons.
