34th Meeting of the AAS Division on Dynamical Astronomy, May 2003
11 Disks
Oral, Wednesday, May 7, 2003, 8:30-10:30am,

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[11.04] Viscous Evolution of an Impact Generated Water/Rock Disk Around Uranus

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

To avoid accretion of substantial hydrogen, it is likely that the final stage of Uranus formation post-dated the bulk of the solar nebula. This renders it unlikely that its satellite system formed from a hydrogen-rich circumplanetary disk, and suggests it might instead be a by-product of a giant impact. Indeed, the 97 degree obliquity of Uranus is often cited as circumstantial evidence that large impacts occurred. Although SPH experiments (Slattery et al. 1989) indicate that sufficient mass and angular momentum can be placed into orbit, it is doubtful that the radius of the resulting disk would be comparable to the dimension of the satellite system; the outer most satellite Oberon resides at 22.3 planetary radii. Here we consider whether a rapid, post-impact spreading of the disk could account for this. The disk is composed primarily of vaporized water and silicates that will condense if the temperature gets too low. A rapid accumulation of the solids would make their further radial transport difficult. On the other hand, the disk temperature can be kept elevated by viscous energy dissipation. We discuss whether a self-consistent model can be constructed and the implied constraints on the effective disk viscosity. Mechanisms such as MHD and/or hydrodynamic turbulence are evaluated as possible sources of the viscosity in this environment.

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

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.