Oral Presentation

On the diversity of satellite systems formed from Roche-interior particle disks

Ryuki Hyodo, Keiji Ohtsuki

In our solar system, most of the planets have satellite systems around them. In systems with a single satellite such as Earth-Moon system, satellite mass is relatively high compared to the host planet’s mass. On the other hand, giant planets such as Saturn, Uranus have multiple- satellite systems. Generally, their inner major satellites called regular satellites exist outside their Roche limit with relatively small mass ratio to the host planet. Those inner satellites are on nearly circular prograde orbits with low inclination. Formation of large regular satellites of Jupiter and Saturn has been explained by accretion in a circumplanetary gas disk (Canup & Ward 2009). On the other hand, Crida & Charnoz (2012) showed that regular satellites of Saturn, Uranus and Neptune can be formed by spreading of ancient massive rings across the Roche limit using one-dimensional analytical model. Formation of satellites from those particle disks was first studied in the context of lunar formation (Ida, S., et al. 1997). Initially, particles are distributed within the Roche limit and their accretion is prohibited. Then, the disk spreads with time. As the disk spreads and the disk materials diffuse beyond the Roche limit, the materials start to form gravitationally bound aggregates. In the case of relatively massive disk, a large single satellite is its outcome (Ida, S., et al. 1997). However, if the initial disk is less massive, the viscosity of the disk is low and the time scale of disk diffusion is much longer. These aspects expect to lead to the different outcomes.

In the present work, we perform large N-body simulations in order to see the evolution of less massive Roche-interior particle disks, and show that another satellite is secondly formed from a residual disk after the formation of the first satellite (Hyodo et al. 2014, ApJ accepted). Moreover, We found that co-orbital satellites are occasionally formed as a natural consequence of the disk spreading. As the number of discovery of the exoplanets increases, the diversity of satellite systems is expected to be found around them.