36th DPS Meeting, 8-12 November 2004
Session 44 Origins and Planet Formation: Satellite Formation
Oral, Friday, November 12, 2004, 10:30am-12:00noon, Clark

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[44.01] A Gas-poor Planetesimal Feeding Model for the Formation of Giant Planet Satellite Systems: Constraints on the Planetesimal Size Distribution

P. R. Estrada (NASA Ames), I. Mosqueira (NASA Ames/SETI Institute)

Given our presently inadequate understanding of the turbulent state of the solar nebula and planetary nebulae, there are two sensible approaches to satellite formation that avoid over-reliance on specific choices for essentially free parameters. The first one postulates turbulence decay. If so, Keplerian disks must eventually pass through quiescent phases, so that the survival of satellites (and planets) ultimately hinges on gap-opening. In this scenario, the criterion for gap-opening itself sets the value for the gas surface density of the satellite disk (Mosqueira and Estrada 2003b).

The second approach assumes that steady turbulence is sufficiently strong to cause the evolution of the gas disk on a shorter timescale than that for satellite formation. This approach uses the turbulence of the subnebula to remove gas from the disk but not to fine-tune the conditions of the subnebular environment. In this case, the gas surface density is left unspecified, though the presence of some gas may help to explain the observations. Satellite formation is then understood in terms of planetesimal dynamics that are largely uncoupled from the gas (somewhat analogous to the case of the terrestrial planets). We will discuss a gas-poor model with the following features: First, collisions between planetesimals in the vicinity of the giant planet leads to the formation of a protosatellite swarm of prograde and retrograde objects extending as far as ~RH/2 (Ruskol 1975, Safronov et al. 1986). Second, this circumplanetary swarm has a small net specific angular momentum which results in the formation of close-in, prograde satellites. Third, close to the planet, hypervelocity impacts can ultimately lead to a variety of outcomes (i.e., Jovian-like versus Saturnian-like satellite systems). Fourth, satellitesimal collisional removal from the outer disk is balanced by planetesimal collisional capture. Excluding satellite embryos, at any given time this disk mass is less than the mass of the regular satellites. Fifth, a satellite formation timescale of 105-106 years (presumably consistent with Callisto's partially differentiated state) controlled by the feeding of planetesimals onto the circumplanetary disk (Mosqueira et al. 2000). Possible constraints on the planetesimal size distribution that can deliver enough material and angular momentum to form the regular satellites of Jupiter and Saturn will be discussed.

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© 2004. The American Astronomical Soceity.