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J. W. Barnes, D. P. O'Brien (University of Arizona LPL)
We investigate the long-term dynamical stability of satellites orbiting extrasolar planets, applying the results of Ward and Reid (1973) and Holman and Wiegert (1999). For planets sufficiently close to their parent star, tides act to despin the planet to an equilibrium rotational state that is a function of orbital eccentricity over relatively short timescales. The synchronous orbit around such despun planets (like geosynchronous orbits around Earth) is farther away from the planet that the outermost stable orbit, meaning that any satellites of the planet will be evolving inward due to tidal interactions. For giant planets within a few tenths of an AU of their parent star, this timescale is shorter than the total age of the system for larger mass satellites, leading to an upper limit on the mass of any surviving primordial moons in these systems. In an extreme but observationally useful case, an upper limit on the mass of any surviving original satellites around HD209458b can be placed at 6* 10-7 MEarth, half as massive as Jupiter's satellite Amalthea. This study compliments the transit observations of Brown et. al. (2001) which yielded an upper mass of 3 MEarth for any companions to HD209458b.
(Ward and Reid, MNRAS 164, pp21-32 (1973); Holman and Wiegert, AJ 117 pp621-628 (1999); Brown et. al., ApJ 552 pp699-709 (2001) )