lissauer_satellites

lissauer_satellites - arXiv:0809.1418v3 [astro-ph] 16 Jan...

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Unformatted text preview: arXiv:0809.1418v3 [astro-ph] 16 Jan 2009 Formation of Jupiter and Conditions for Accretion of the Galilean Satellites P. R. Estrada, and I. Mosqueira SETI Institute J. J. Lissauer, G. DAngelo, and D. P. Cruikshank NASA Ames Research Center Abstract We present an overview of the formation of Jupiter and its associated circumplanetary disk. Jupiter forms via a combination of planetesimal accretion and gravitational accumulation of gas from the surround- ing solar nebula. The formation of the circumjovian gaseous disk, or subnebula, straddles the transitional stage between runaway gas accretion and Jupiters eventual isolation from the circumsolar disk. This isola- tion, which effectively signals the termination of Jupiters accretion, takes place as Jupiter opens a deep gas gap in the solar nebula, or the solar nebula gas dissipates. The gap-opening stage is relevant to subnebula formation because the radial extent of the circumjovian disk is determined by the specific angular momen- tum of gas that enters Jupiters gravitational sphere of influence. Prior to opening a well-formed, deep gap in the circumsolar disk, Jupiter accretes low specific angular momentum gas from its vicinity, resulting in the formation of a rotationally-supported compact disk whose size is comparable to the radial extent of the Galilean satellites. This process may allocate similar amounts of angular momentum to the planet and the disk, leading to the formation of an ab-initio massive disk compared to the mass of the satellites. As Jupiter approaches its final mass and the gas gap deepens, a more extended, less massive disk forms because the gas inflow, which must come from increasingly farther away from the planets semimajor axis, has high specific angular momentum. Thus, the size of the circumplanetary gas disk upon inflow is depen- dent on whether or not a gap is present. We describe the conditions for accretion of the Galilean satellites, including the timescales for their formation and mechanisms for their survival, all within the context of key constraints for satellite formation models. The environment in which the regular satellites form is tied to the timescale for circumplanetary disk dispersal, which depends on the nature and persistence of tur- bulence. In the case that subnebula turbulence decays as gas inflow wanes, we present a novel mechanism for satellite survival involving gap opening by the largest satellites. On the other hand, assuming that sustained turbulence drives subnebula evolution on a short timescale compared to the satellite formation timescale, we review a model that emphasizes collisional processes to explain satellite observations. We briefly discuss the mechanisms by which solids may be delivered to the circumplanetary disk. At the tail end of Jupiters accretion, most of the mass in solids resides in planetesimals of size > 1 km; however, planetesimals in Jupiters feeding zone undergo a period of intense collisional grinding, placing a significant...
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lissauer_satellites - arXiv:0809.1418v3 [astro-ph] 16 Jan...

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