Are Giant Planet Satellites Mini-solar Systems?

Details Are Giant Planet Satellites Mini-solar Systems? Are Giant Planet Satellites Mini-solar Systems?

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p51f..05m&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P51F-05

Physics

6200 Planetology: Solar System Objects (New Field), 6218 Jovian Satellites, 6220 Jupiter, 6280 Saturnian Satellites, 6299 General Or Miscellaneous

Scientific paper

The regular satellites of Jupiter and Saturn exhibit a number of characteristics strongly suggestive of formation in a thin (aspect ratio H/r ˜ 0.1) circumplanetary gas disk (Mosqueira and Estrada 2003a). Also, the mass ratio of the largest satellites to the primary μ ˜ 10-4 lead one to think of these satellite systems as scaled-down solar systems. Yet, the larger mass ratio for the giant planets to the primary μ ˜ 10-3 appears to limit the usefulness of the planet-satellite analogy. If gap-opening determines the final size of at least Jupiter (Lin and Papaloizou 1993), then significantly smaller objects would be unable to truncate the disk. There are, however, at least two significant difficulties with this point of view. First, the non-linear or thermal gap-opening criterion (Lin and Papaloizou 1993) does not yield a Jupiter mass. Second, the migration timescale due to planet-disk interactions (Ward 1997) is too fast for the formation of giant planets through the core accretion process (Pollack et. al 1996) despite recent work which has lengthened it by up to an order of magnitude (Tanaka et al. 2002, D'Angelo et al. 2002, Bate et al. 2003). An alternative viewpoint has accretion taking place in a weakly turbulent disk, and the survival of both planets and satellites a direct consequence of gap-opening. In this view at least the largest satellites (Mosqueira and Estrada 2003b) and planetary cores ( ˜ 10 M⊕ ; Rafikov 2002) were able to open gaps in the disk. However, because the waves launched by such pertubers do not become non-linear immediately, the gap begins to form a distance away from the perturber given by the shocking length of acoustic waves (Goodman and Rafikov 2001; Rafikov 2002). Estrada and Mosqueira (2003) have suggested that the annulus of material adjacent to the proto-planet that immediately precedes the runaway gas accretion phase (Pollack et al. 1996) can be used to provide the mass needed to lead to the formation of a giant planet. If so, the dilemma posed by Type I migration (Ward 1997) is mitigated, and the analogy between satellites and planets gains currency. It is possible to argue that an alternative solution to this issue may involve lowering the migration rate even further, but one should keep in mind that slower migration might allow even smaller objects to open gaps. Here we look into the issues raised by this annulus of material in the satellite context, and argue that it may not prevent satellite survival. This work was supported by a NASA PGG grant and the NRC.

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