Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.6107m&link_type=abstract
American Astronomical Society, DPS meeting #42, #61.07; Bulletin of the American Astronomical Society, Vol. 42, p.1089
Astronomy and Astrophysics
Astronomy
Scientific paper
The Galileo mission to Jupiter yielded the normalized moment of inertia of Ganymede (0.312) and Callisto (0.355), while the Cassini spacecraft has measured Titan's moment of inertia (0.34; Iess et al. 2010). Callisto's moment of inertia can be fitted using a two-layer interior model with at least a 300 km water-ice shell and an undifferentiated ice and rock-metal interior (Schubert et al. 2004), whereas Titan's moment of inertia is consistent with a thicker 700 km water-ice shell, and Ganymede's moment of inertia implies full differentiation. Key satellite formation parameters that can explain this trend are the accretion timescale and the subnebula temperature at the location of the proto-satellite. Mosqueira and Estrada (2003a,b) investigate a non-local model that forms Ganymede in 104 yrs, Titan in 105 yrs and Callisto in 106 yrs. Satellites located in the outer disk take longer to accrete because they derive solids from an extended, lower density region of the subnebula; indeed in this model the timescale of accretion is set by inward gas-drag drift time of (Hyperion-like) 100 km satellitesimals. Since satellitesimals originate from exterior orbits, the temperature of the subnebula at the location of Ganymede 250 K, Callisto 150 K, and Titan 100 K (Mosqueira and Estrada 2003a) provides a rough constraint on the interior temperature of each satellite (after correction for the effects of compression and radioactive heating) as well as the background radiation temperature during satellite accretion. We argue that these parameters provide a natural explanation for the observed moment of inertia trend; we expect that the interior of Titan and Callisto remain too cold for full differentiation to take place (unless Titan's interior were fully differentiated with a hydrated rocky core). This work is supported by NASA PG&G and OPR grants.
Estrada Paul R.
Mosqueira Ignacio
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