Final Origin of the Saturn System
, A. Reufer
UC, Santa Cruz,
University of Bern, Switzerland.
Saturn’s middle-sized moons (MSMs) are of diverse geology and composition, totaling 4.4% of the system mass. The rest is Titan, with more mass per planet than Jupiter’s satellites combined. Jupiter has four large satellites with 99.998% of the system mass, and no MSMs. Models to explain the discrepancy exist (e.g. Canup 2010; Mosqueira et al. 2010; Charnoz et al. 2011) but have important challenges. We introduce a new hypothesis, in which Saturn starts with a comparable family of major satellites (Ogihara and Ida 2012). These satellites underwent a final sequence of mergers, each occurring at a certain distance from Saturn. Hydrocode simulations show that galilean satellite mergers can liberate ice-rich spiral arms, mostly from the outer layers of the smaller of the accreting pair. These arms gravitate into clumps 100-1000 km diameter that resemble Saturn’s MSMs in diverse composition and other major aspects. Accordingly, a sequence of mergers (ultimately forming Titan) could leave behind populations of MSMs at a couple of formative distances, explaining their wide distribution in semimajor axis. However, MSMs on orbits that cross that of the merged body are rapidly accumulated unless scattered by resonant interactions, or circularized by mutual collisions, or both. Scattering is likely for the first mergers that take place in the presence of other resonant major satellites. Lastly, we consider that the remarkable geophysical and dynamical vigor of Titan and the MSMs might be explained if the proposed sequence of mergers happened late, triggered by impulsive giant planet migration (Morbidelli et al. 2009). The dynamical scenario requires detailed study, and we focus on analysis of the binary collisions. By analysis of the hydrocode models, we relate the provenance of the MSMs to their geophysical aspects (Thomas et al. 2010), and consider the geophysical, thermal and dynamical implications of this hypothesis for Titan’s origin.
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44th DPS Program published in BAAS volume 44 #5.
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