Flying Exomoons on Jumping Jupiters
My most recent research work studies how planet-planet scattering affect the orbital stability of moons of extra-solar giant planets, using N-body numerical simulations.
[Planet-Planet Scattering]
Extra-solar giant planets are expected to form closely packed, so they develop orbit crossing and close encounters. This unstable phase ends with one or multiple planets removed by collision or ejection from the system.
UpsAnd_NSF.mov[Moons in Planet-Planet Scattering]
The planet-planet scattering environment provides many sources of strong perturbations for the orbits of moons. Direct perturbation of planetary close encounters, violation of Hill stability, highly inclined systems, and high obliquity planets etc., could all make moons unstable. In such scenarios, the dynamical outcomes of exomoons are interestingly diverse and some very novel, and, not surprisingly, most of moons experience removal from the system.
The bulk of stable moons lie within 0.1 Hill radii from the moon hosting planet, and moons on Galilean-moon like orbital distances have 0.2 - 0.4 probability of remaining stable. Some interesting and novel dynamical outcomes includes moons captured by a different planet, moons that turned to orbit the star, moons stable around ejected free-floating planets. The most frequent outcome of all is moons being flung out of the system as free-floating exomoons.
The high frequency of moon ejection could lead to 0.01-1 free-floating exomoons per star in our galaxy.
On the left: moon capture by the passing perturber in a planet-planet close encounter event. This is a finely tuned configuration, in which the orbital velocity of the moon is aligned with the acceleration from the perturbing planet, and the moon is in close proximity with the perturbing planet.