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D.J. Asher, A.A. Christou (Armagh Observatory)
Knowledge of the masses of planetary satellites is valuable as it can be used to constrain their densities and thus their origin and collisional history by proxy. We search for close encounters between irregular satellites of the outer planets up to a few decades from the present, looking in particular for cases where the mass of one satellite has an observable effect on the motion of the other. A formula which specifies the impulse to the perturbed satellite's semi-major axis as a function of the distance and speed of the encounter combined with reasonable mass estimates of the perturbing satellite allows these interesting cases to be identified. The change in semi-major axis leads to a linear divergence in mean anomaly, relative to the model where the perturbing satellite is assumed massless. For reasonably immediate practical value, measurable consequences on the perturbed satellite's sky position within a time frame of a decade or so after the encounter are desired.
Here, in a manner similar to what has been done for the asteroid belt (e.g. Michalak 2001, Astron. Astrophys., 374, 703), we predict which satellites should be monitored astrometrically for signatures of close encounter impulses over time. Our results are relevant to conventional long-term ground-based astrometric campaigns as well as future space-based astrometric projects such as GAIA.
Research at the Armagh Observatory is funded by the Northern Ireland Department of Culture, Arts and Leisure.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.