DPS 2001 meeting, November 2001
Session 25. Solar System Origins II
Oral, Chairs: M. Drake, H. Levison, Wednesday, November 28, 2001, 5:00-6:30pm, Regency GH

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[25.01] Satellite formation in a circumjovian accretion disk

R. M. Canup, Wm. R. Ward (Southwest Research Institute)

A scenario is considered in which the Galilean satellites form within a cicumjovian accretion disk produced during the very end stages of gas accretion (e.g., Lubow et al. 1999). We assume an inflow of gas and solids with some characteristic maximum specific angular momentum with respect to the planet. A quasi-steady state circumplanetary gas disk is produced through a balance of the inflow supply and the disk's internal viscous evolution (Lynden-Bell and Pringle 1974; Coradini et al. 1989; Canup and Ward 2001). Once in circumplanetary orbit, inflowing solids accumulate into objects large enough to decouple from the gas on time scales much shorter than their lifetime against inward decay. Both the total mass of solids and the solids-to-gas mass ratio in the disk thus build-up over time, with satellites accreting at a rate regulated by the inflow flux.

Two basic constraints on the Galilean satellite formation environment are 1) disk temperatures near Ganymede's orbit low enough for accretion of ice, and 2) overall formation times > 105 - 106 years (Lane and Stevenson, Pers. Com.) for consistency with Callisto's apparent partially differentiated state (e.g., Anderson et al. 1998). Both requirements constrain the inflow rate, F, implying F < MJ/(few x 106 yrs) for a solids-to-gas mass ratio in the inflowing material of 0.01, where MJ is a Jovian mass. Such slow inflow rates yield a much lower disk steady-state gas surface density than is implied by augmenting the mass of the current satellites to solar elemental composition. Instead, the solids-to-gas mass ratio in the disk will exceed unity as the mass of disk solids approaches that of the Galilean satellites.

This work is supported by NASA's Planetary Geology and Geophysics Program.

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