Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p12c..04p&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P12C-04
Physics
6040 Origin And Evolution, 6218 Jovian Satellites
Scientific paper
If the Galilean satellites accumulated with comparable time scales in a mass starved disk of gas and particles during the last stages of accretion of Jupiter (Canup and Ward, 2002), a more rapid disk induced inward migration of Ganymede compared with Europa and Io allows capture of the satellites into the Laplace relation, n1-3n_2+2n_3=0, where ni are the mean orbital angular velocities of Io, Europa and Ganymede respectively. The rapid growth of the orbital eccentricities during migration must be damped by a disk interaction to prevent instability. The eccentricities during migration within the resonances are e1, e_2, e_3≈ 0.065, 0.15, 0.002 if ˙ ei/e_i=30˙ ai/a_i, compared to 0.0041, 0.0101 and 0.0006 today, where ai and ei are orbital semimajor axes and eccentricities. Whether or not these larger eccentricities will influence the thermal histories of the satellites depends on the duration of the migration phase. At the present time conjunctions of Io and Europa occur at Io's periapse and Europa's apoapse, and conjunctions of Europa and Ganymede occur when Europa is at its periapse and Io is on the opposite side of Jupiter. The phase of Ganymede during conjunctions is not constrained. For the large eccentricities during migration, conjunctions occur at odd angles. Continued eccentricity damping after the migration has stopped because of disk dispersal brings the system to the current configuration---even the detail of the resonance angle that includes Ganymede's periapse longitude changing from libration to circulation. This scenario differs drastically from the currently accepted origin of the resonances, where differential expansion of the orbits from tides raised on Jupiter results in sequential capture in the Io-Europa resonances and the Europa-Ganymede resonance along with the Laplace 3 body resonance, with intense tidal dissipation in Io damping the amplitudes of libration to very small values (Yoder, 1979). The constraints on QJ of Jupiter imposed in the Yoder scenario are not relaxed for a primordial origin. There is no a priori reason to assume that QJ could not be presently near ~ 2x 104 (a factor of 3 smaller than the historically averaged lower bound) to maintain the current configuration in equilibrium with the measured heat flux of 3 W/m2, although a theory is still being sought to support such a low QJ.
Lee Minchul
Peale Stanton J.
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