The Orbits of the Retrograde Jovian Satellites

Abstract

The orbits of Jupiter's four retrograde satellites are strongly perturbed by the Sun and therefore resist treatment by the perturbative methods of classical celestial mechanics. We have integrated the orbits of these satellites over an interval of 2 Myr. We confirm the finding of A.L. Whipple and P.J. Shelus (1993, Icarus 101, 265-271) that the apsis of Pasiphae is locked to Jupiter's apsis, and find that Sinope's apsis is intermittently locked in the same resonance. Sinope also participates in a 1:6 mean motion resonance with Jupiter, and its orbit is chaotic with an inverse Liapunov exponent of 5000 yr. The finding that two of the four satellites are locked in this secular resonance constrains theories of the formation of the retrograde satellites; in particular it suggests that slow orbital evolution, perhaps through dissipation or changes in Jupiter's mass, played an important role in establishing their present orbits. © 1993 by Academic Press, Inc.