Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.3209b&link_type=abstract
American Astronomical Society, DPS meeting #39, #32.09; Bulletin of the American Astronomical Society, Vol. 39, p.475
Astronomy and Astrophysics
Astronomy
Scientific paper
Radio tracking data from close spacecraft flybys of Saturn's satellite Rhea and Jupiter's satellite Callisto suggest that both bodies are partially differentiated, with interiors composed of a homogeneous ice/rock mixture (Anderson et al., 2001; Anderson & Schubert, 2007; Iess et al., 2007). If these satellites are partially differentiated at present, they must have avoided melting during formation, when they were heated by deposition of accretional energy and potentially by aluminum-26. Estimates of the temperature rise associated with the balance between radiogenic heating, accretional heating from small impactors that deposit energy close to the satellite's surface, and maximally efficient radiative cooling are used to constrain the timing and of each satellite's formation relative to the origin of CAI's as a function of the satellite's accretion time scale and protsatellite disk temperature. If Rhea accreted slowly (in 0.1 to 1 Myr), its growth must have finished no earlier than 2 Myr after CAI's to avoid melting in excess of that allowed by current moment of inertia constraints. Faster accretion requires a later formation time for Rhea as a function of disk temperature. To avoid accretional melting, Callisto must be assembled slowly, over a time scale longer than 2 Myr, and it must finish forming no earlier than 5 Myr after CAI's. In the context of the Canup & Ward (2002) satellite formation model, the implied ages suggest that gas inflow to Jupiter ceased no earlier than time scales comparable to average nebular lifetimes inferred from observations of circumstellar disks (e.g., Haisch et al., 2001).
Barr Amy Courtright
Canup Robin M.
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