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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[11.02] Constraints on the Size of the Circumplanetary Gas Disk

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

Based on the dynamical properties of the irregular satellites of Jupiter (Saha and Tremaine 1993; Cuk and Burns 2001) and the separation between the regular and irregular satellites of the giant planets of Jupiter, Saturn, and Uranus, Mosqueira and Estrada (a,b 2003, in press in Icarus) argued that the regular satellites of the giant planets formed in a disk extending out to the position of the irregulars at ~RH/5, where RH is the Hill radius of the planet, thus irregular satellites with smaller semi-major axis would have been lost due to gas drag. The recent discovery of irregular satellites of Neptune between 0.17-0.19 RH (Nicholson, personal communication) fits with this view (though observational issues cloud the picture to some extent).

But what sets the size of the outer gas disk? One possibility is that the specific angular momentum of gas accreted by Jupiter determines it. Here we explore the alternative possibility that the circumplanetary gas disk once extended farther out, but the resonant tidal torque of the Sun on the circumplanetary gas disk reduced its size. If so, some of the angular momentum of accretion may end up in Jupiter's orbit instead of its spin angular momentum or the angular momentum of the gas-augmented satellite disk. To make progress we need to ask whether any resonant locations of the Sun fall within the disk. Due to the low frequency of the Sun's orbit the m = 2 horizontal Lindblad resonance falls far from the location of the irregulars at ~RH. An m = 2 vertical resonance (Lubow 1981) is located at ~RH/2, which may set the maximum allowable size for the circumplanetary gas disk, but is still well outside the location of the innermost irregulars. This leads us to consider resonances that arise from the eccentricity of the binary orbit, allowing for the possibility that the eccentricities of the giant planets were significantly larger in the past.

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