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K. Aksnes (Institute of Theoretical Astrophysics, Univ. of Oslo, Norway), F.A. Franklin (Center for Astrophysics, Cambridge, U.S.A.)
Timings and light curves of mutual satellite events of the Galilean satellites in 1908, 1914, 1926 and 1973-1997 have been used to improve the values of the most important parameters in Sampson's satellite theory, and to solve for a rate of change dn1/dt of Io's mean motion n1.
For the fractional acceleration dn1/dt/n1, we find a preliminary value of 2.88 ±.10, in units of 10-10. This is in fair agreement with the values 3.3 ±.5 and 4.54 ±.95 determined, respectively, by de Sitter(1928) and Goldstein & Jacobs(1995) by analyzing satellite eclipses by Jupiter and some photographic observations. Our value also agrees well with the value 3.20 ±.89 found by Greenberg et al.(1986) based on the measured heat loss from Io, neglecting the Jovian tidal torque. However, by assuming resonance equilibrium (dn1/dt - 2dn2/dt = dn2/dt - 2dn3/dt), they found the value -1.16 ±.31, while Lieske(1987) found the slightly negative value -0.074 ±.087 from eclipse timings.
Our results imply that Io is now spiraling slowly inwards, loosing more orbital energy from dissipation in Io than what is gained from Jupiter's tidal torque.
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