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P. R. Estrada (NASA Ames), I. Mosqueira (NASA Ames/ SETI Institute)
Protoplanets migrate inwards due to the tidal interaction with the nebula disk (Goldreich and Tremaine 1980; Ward 1986). In a minimum mass solar nebula an inwardly migrating protoplanet may open a gap and stall when it reaches a mass between 2-15 MEarth provided \alpha < 10-4 (Rafikov 2002), thus improving its chances of survival. Yet the migration time of a protoplanet in a minimum mass solar nebula may be significantly faster than the formation time of a sufficiently large planetary core (~10 MEarth) to allow gas accretion. However, recent analytical work (Tanaka et al. 2002) and numerical simulations (D'Angelo et al. 2002; Bate et al. 2003) have increased the timescale of migration by up to an order of magnitude (depending on disk conditions and whether the corotation resonance saturates or not) compared to previous estimates (Ward 1997). Furthermore, increasing the gas surface density with respect to the minimum mass solar nebula may shorten the formation time of a planetary core (Tanaka and Ida 1999). Provided that a planetary core formed at Jupiter's location in time to open a gap, and that the nebula was weakly turbulent at the time of its formation, gap-opening might have left Jupiter in its present orbit far from the Sun. The issue then arises as to what determines the final mass of the planet. Here we consider the possibility that Jupiter accreted its mass from an annulus of gas within the shocking distance of acoustic waves (Goodman and Rafikov 2001) launched by the growing protoplanet, estimate the gas surface density based on this assumption, and compute the gap-opening critical mass in such a disk. A similar argument applied to the outer giant planets would require lower gas surface densities outside Jupiter, which may be incompatible with a strongly turbulent disk. However, this argument is complicated by the effective viscosity due to the planetary tidal torques themselves. A possible role for the thermal condition will be discussed.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.