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[35.06] Io's secular acceleration and Jupiter's dissipative function Q

K. Aksnes (Institute of Theoretical Astrophysics, University of Oslo, Norway), F. A. Franklin (Center for Astrophysics, Cambridge, MA)

In a recent paper (Astron. J. 122:2734,2001) the authors have used 520 observations of mutual events of the four Galilean satellites between 1908 and 1997 to solve for the main constants in Sampson's theory, including the mean motions n_i and their rates dn_i/dt. Because of strong correlations, it is not possible to obtain meaningful least-squares solutions for both n_i and dn_i/dt, except for Io for which we obtain a mean motion correction dn₁ = (0.4±1.1)10^-6deg/day and (dn₁/dt)/n₁ = 3.6±1.0 in units of 10^-10yr^-1. This dn₁ value is comparable to the values determined for dn₂, dn₃ and dn₄. Although the data can be satisfied nearly as well by correcting only the n_i's, this leads to a ten times larger dn₁ value, which seems unacceptably large. Furthermore, dn₁/dt = 0 would require an unphysically large tidal torque from Jupiter to overcome Io's orbital decay because of the observed energy dissipation in Io. Our determination of (dn₁/dt)/n₁ is in reasonable agreement with the values 3.3±0.5 and 4.54±0.95 obtained by de Sitter (1928) and Goldstein & Jacobs (1995) but conflicts with the value -0.074±0.087 found by Lieske (1987), mainly from timings of ordinary eclipses. Our results imply that Io is now spiraling slowly inward, losing more orbital energy from dissipation than it gains from Jupiter's orbital tidal torque. These results suggest that the specific dissipation function of Jupier, Q, is around 200,000 for an Io heat flux of 1.3x10¹⁴W.

If the author provided an email address or URL for general inquiries, it is as follows:

kaare.aksnes@astro.uio.no

Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.