Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p21c..01c&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P21C-01
Physics
[6218] Planetary Sciences: Solar System Objects / Jovian Satellites, [6265] Planetary Sciences: Solar System Objects / Planetary Rings, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites
Scientific paper
The Jovian and Saturnian regular satellites likely formed within circumplanetary disks of gas (primarily hydrogen) and solids (rock and ice). Here I will focus on a model [1-3] in which gas giant satellites form within disks produced by the final stages of gas accretion by the planets [4]. Small solids carried into the disk by gas inflowing from solar orbit provide the raw material for accreting satellites. Each satellite can grow no larger than a critical mass, at which point its orbit spirals into the planet due to density wave interactions with the gas disk (Type I migration). This critical mass is comparable to those of the Galilean satellites and Titan. Multiple generations of satellites having this critical mass are predicted to form and be lost to collision with the planet. The final surviving satellites are those that form as gas inflow to the planet ends, the circumplanetary gas disk dissipates, and the satellite orbits stabilize. In this model, all the gas giant satellites accrete slowly, at a rate governed by the rate of delivery of solid material to the disk. This implies that the final large satellites form on a timescale comparable to the solar nebula dissipation timescale, which was likely ~ 10^6 yr. Such a slow accretion can allow large, outer ice-rock satellites to remain undifferentiated or to undergo only partial differentiation as they form [5-6]. The model produces final satellite systems having either several large satellites (like the Galilean satellites) or a single large satellite (like Saturn’s Titan) [2,7]. A Saturn-like system is produced when large, Titan-sized satellites orbiting interior to Titan spiral into the planet and are lost as gas inflow ends, leaving Titan as the sole large survivor [2]. As the final large satellite lost from the Saturn system spirals within the Roche limit, planetary tides preferentially strip material from its outer layers, producing a massive ice ring [8]. Such conditions offer a new explanation for the origin of Saturn’s main rings and the Saturnian ice-rich satellites interior to and including Tethys [8]. [1] Canup, R.M. & W.R. Ward, AJ, 124, 3404 (2002); [2] Canup, R.M. & W.R. Ward, Nature 441, 834 (2006). [3] Ward, W.R. & R.M. Canup, In Europa, Univ. Az. Press (2009). [4] Ward, W.R. & R.M. Canup, AJ, in press (2010); [5] Barr, A.C. & R.M. Canup, Icarus 198, 163 (2008); [6] Barr, A.C., Citron, R. & R.M. Canup, Icarus, in press (2010); [7] Sasaki, T., G.R. Stewart, & S. Ida. ApJ, 714, 1052 (2010). [8] Canup, R.M., Nature, submitted (2010). Support from NASA’s OPR and PGG programs is gratefully acknowledged.
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