|M.Sc Student||Roi Rahin|
|Subject||Formation and dynamical evolution of moons around gas giant|
|Department||Department of Physics||Supervisor||Professor Perets Hagai|
|Full Thesis text|
Moons around gas giant planets such as Jupiter are divided into 2 groups of regular and irregular moons. The two groups are most commonly separated by distance, eccentricity and inclination, with regular moons having a relatively close orbit ( R ∼ 10 Rp ), low eccentricity ( e<0.01 ) and low inclination (typically i< 1o) and irregular satellites having a semi-major axis greater by an order of magnitude and high eccentricities and inclinations, many of them with retrograde orbits. The two groups also differ by mass with regular moons possessing most of the mass of the moon system. Accordingly, it is usually assumed that each group is formed via a different and unrelated process. Regular moons are assumed to be formed in a circumplanetary accretion disk whereas irregular moons are assumed to be formed via capture mechanisms. The formation of regular moons assumes formation within a truncated gas disk, which does not agree with contemporary gas disk structure simulations. Because of this discrepancy and other issues with both forms of moon formation (capture and formation in a disk) we propose an in-situ origin for both regular and irregular moons. In particular we suggest that irregular moons are not external asteroids/KBOs (Kuiper Belt Objects) captured from heliocentric orbits, but rather bodies that formed at the outer extension of the circumplanetary disk. The disk structure model was taken from simulation results for a tidally truncated disk, which make no assumption as to the maximum distance material can viscously spread to. In order to test our model we have modified an n-body simulation to include interactions between satellites and the accretion disk and simulated possible formation of moons in such an accretion disk around Jupiter and Uranus. We do not model the gaseous disk directly, rather we model the interactions between the bodies surrounding the gas giant and the circum-planetary disk using the results of the tidally truncated disk simulations. Our simulations yield several interesting results. First, in many simulations we see a formation of a group of moons which share characteristics with regular moons. This suggests that it is unnecessary for accretion disks to be truncated in order to form the regular moons observed. Second, in many simulations a second group of moons emerges. The characteristics of this second group are different from those of the first group and bear a resemblance to those of irregular moons. We conclude that the possibility of in-situ formation of irregular moons cannot be easily discounted and by improving the simulation it may be possible to demonstrate formation of irregular moons via accretion disk.