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D.J.G.J. Hestroffer (IMCCE/Paris observatory)
Cohesionless rubble-pile asteroids have already been thought to have shapes of hydrostatic equilibrium (Farinella et al. Icarus 46, 114), but observational evidence showed that this is not the case. In contrast asteroids have a much broader distribution in shape which moreover is not connected to ellipsoidal figures of hydrostatic equilibrium (Holsapple 2001 Icarus 154, 432). However it is shown here that there remain a few candidates among the binary asteroids population that could possibly be on the Jacobi sequence (45 Eugenia, 87 Sylvia and 107 Camilla), rehabilitating hence the original idea of Farinella et al. Not only their shape is close to a Jacobi ellipsoid but also their estimated adimensional rotational frequency (spin period and bulk density) is consistent with figures of equilibrium of inviscid, incompressible fluids. In addition their macroporosity could be consistent with that of randomly packed rubble. This means that the surface of such bodies would actually correspond to equipotentials whatever the friction between the agregates. It is noted that the few candidates are relatively large asteroids possesing a small satellite. If this equilibrium shape hypothesis is confirmed it will put additional constraints on their collisional history. Further mass determination are needed to test this hypothesis and find other possible candidates.
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Bulletin of the American Astronomical Society, 36 #2
© 2004. The American Astronomical Soceity.