35th Meeting of the AAS Division on Dynamical Astronomy, April 2004
Session 9 Satellites \& Rings
Oral, Friday, April 23, 2004, 2:20-5:35pm,

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[9.04] The gravitational stirring of the irregular prograde satellites of Jupiter

A. Christou (Armagh Observatory, Northern Ireland, UK)

The irregular satellites of Jupiter exhibit groupings in proper element space that are thought to originate from the post-capture collisional fragmentation of one or more parent bodies (Gladman et al, Nature 412, 163, 2001; Sheppard & Jewitt, Nature 423, 261, 2003; Nesvorný et al, Astron. J. 126, 398, 2003). The Himalia prograde group contains five known members and is spectrally homogeneous, arguing for a single progenitor body being responsible for the observed population. However, this hypothesis is difficult to reconcile with the large orbit-to-orbit velocities within the group. In particular, the relative orbital velocity between the two largest satellites, Himalia and Elara, is 175 m/sec, the largest Himalia-relative velocity within the group with the exception of S/2000 J11. Moreover, the velocity dispersion of the remainder of the group with respect to Elara is as large as 320 m/sec. All these values are significantly larger than the <100 m/sec expected from laboratory experiments and hydrocode simulations.

Here I investigate a process that can potentially resolve this quandary, namely the post-collisional modification of the satellites' orbits due to the cummulative gravitational effects of satellite-to-satellite encounters over Gyr time scales. I have carried out numerical simulations of the long-term dynamical evolution of the orbits for plausible values of the satellites' masses, particularly Himalia. I show that significant orbital migration is likely to have occured over the age of the solar system. Finally, I discuss the circumstances under which this migration can explain the large present-day velocity dispersion of the prograde group, how future measurements of the system can serve to further constrain this scenario and implications for satellite groups of the other gas giants. Astronomical research at the Armagh Observatory is funded by the Northern Ireland Department of Culture, Arts and Leisure (DCAL).

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Bulletin of the American Astronomical Society, 36 #2
© 2004. The American Astronomical Soceity.