Publication Date:
2012-12-30
Description:
Available online 28 December 2012 Publication year: 2012 Source: Icarus Saturn is orbited by a half dozen ice rich middle-sized moons (MSMs) of diverse geology and composition e.g. ( Smith et al., 1981; Thomas, 2010; Schenk et al., 2011 ) that comprise ∼4.4% of Saturn’s satellite mass. The rest is Titan, more massive per planet than Jupiter’s satellites combined. Jupiter has no MSMs. Disk-based models to explain these differences exist e.g. ( Sasaki et al., 2010; Canup, 2010; Mosqueira et al., 2010a; Charnoz et al., 2011 ) but have various challenges and assumptions. We introduce the hypothesis that Saturn originally had a ‘galilean’ system of moons, comparable to Jupiter’s, that collided and merged, ultimately forming Titan. Mergers liberate ice-rich spiral arms, in simulations, that self-gravitate into escaping clumps resembling Saturn’s MSMs in size and compositional diversity. We reason that MSMs were spawned in a few such collisions around Saturn, while Jupiter’s original satellites stayed locked in resonance. The dynamical validity of our scenario depends on whether some MSMs can be scattered or otherwise migrated to stable orbits following each collision, before they are accreted. If satellite formation concludes with a ‘late stage’ of giant impacts e.g. ( Ogihara and Ida, 2012 ) then MSMs could have formed originally by this mechanism. More speculatively, solar-system-wide dynamical upheaval e.g. ( Tsiganis et al., 2005; Morbidelli et al., 2009 )might have triggered final mergers, leaving behind young MSMs and a dynamically excited Titan. Highlights ► We propose that Saturn originally had a family of Galilean-like satellites that collided and merged. ► Simulations of these mergers result in the formation of escaping, clump-forming, ice-rich spiral arms. ► Clump sizes and compositions in these simulations resemble Saturn’s middle-sized moons (MSMs). ► MSM-forming collisions would have occurred over a wide range of orbital dis-tances from Saturn. ► Late collisions triggered by solar system upheaval could explain extraordinary aspects of the Saturn system
Print ISSN:
0019-1035
Electronic ISSN:
1090-2643
Topics:
Physics
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