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J. W. Weiss, G. R. Stewart (CU/LASP)
With the discovery of ``hot Jupiters" (Marcy, G. and P. Butler, 1998, ``Detection of Extrasolar Giant Planets" Annual Review of Astronomy and Astrophysics, 36), , migration of planets due to planet-disk interactions has become widely accepted as an explaination for these bodies. Migration of these planets could have serious effects on any moons that the planets might have. It is clear that if the planet migrates in so close to its star that a moon is no longer within the Hill sphere (the region where the planet's gravity dominates over the star's), the moon will be lost. However, it is not immediately obvious when and how this loss occurs.
Using Hill's approximation, we have integrated orbits of moons as their parent planet migrates inward over a period of approximately 10,000 years. We find that prograde orbiting moons drift away from their planets. Retrograde moons, on the other hand, migrate inwards towards their planets. In both case, however, the Hill radius shrinks fast enough to leave the moons outside of the Hill sphere. We find that when a prograde moon orbits at about 0.5 Hill radii from the planet, it becomes lost. The corresponding loss point for retrograde moons is 1 Hill radius, indicating that retrograde moons will be retained longer. These results are in agreement with Hamilton and Burns 1991 (Icarus, 92, pp. 118-131).
In particular, for a moon which begins at 0.1 Hill radii from a Jupiter-like planet (in terms of mass and orbital semi-major axis), prograde moon loss occurs at roughly 1.3 AU from the parent star, while retrograde moons are lost at 0.1 AU. For prograde moons starting at 0.01 Hill radii from their planets under the same conditions, loss occurs at approximately 0.1 AU. We have not seen retrograde moons at this distance being lost in our simulations. For comparison, the Galilean moons all orbit between 0.008 and 0.03 Hill radii from Jupiter at present.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.