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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[25.03] Satellite Migration and the Evolution of the Gas Disk

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

Survival timescales for satellites in an optically thick giant planet subnebula are typically short compared to the lifetime of the gas disk. It might be hoped that satellites would open a gap in the subnebula, but satellites whose Hill spheres are smaller than the scale-height of the subnebula h may not open a gap (Lin and Papaloizou 1993, In Protostars and Planets III, 749). Only Ganymede and Titan are sufficiently massive to satisfy this constraint.

To make progress we first need to characterize the viscosity properties of the subnebula. Both theoretical and numerical work have shown that nebula turbulence requires a source of "stirring" to be self-sustaining. At present, the best candidate mechanism to generate turbulence with alpha in the range 10-2-10-4 is an entropy gradient in the subnebula leading to a non-barotropic equation of state (Klahr and Bodenheimer, in press). Such a model leads to turbulence that is a function of position and time.

For a satellite to survive in the inner disk the timescale of satellite migration must be longer than the timescale for gas dissipation. For large satellites ~1000 km migration is dominated by the gas torque. Here we look into the possibility that the feedback reaction of the gas disk caused by the redistribution of gas surface density around satellites with masses larger than the inertial mass (Ward 1997, Icarus 126, 261) causes a large drop in the drift velocity of such objects, thus greatly improving the likelihood that they will be left stranded following gas dissipation. For this mechanism to work the angular momentum the satellite launches at resonance locations with wavenumber m ~r/h must be damped in a lengthscale ~h, where most of the torque is exerted. Unlike viscous damping and radial non-linear shock dissipation, vertical wave refraction in the optically thick subnebula and non-linear dissipation at the disk surface (Lin and Papaloizou 1993) may satisfy this requirement, at least for inward travelling waves (Tanaka and Ward, 2000, DPS). We adapt the inertial mass criterion to include gas drag, and m dependent non-local deposition of angular momentum. We find that such a model holds promise in explaining the survival of satellites in the subnebula as well as the mass to distance relationship apparent in the Saturnian and Uranian satellite systems.

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