CAPTURE IN EXTERIOR MEAN-MOTION RESONANCES DUE TO POYNTING-ROBERTSON DRAG

In this paper we discuss the process of resonance trapping, due to rad iation pressure and Poynting-Robertson drag, in the frame of the plana r circular restricted problem of three bodies. We consider the average d resonant equations and search for stationary solutions (i.e., librat ions) which may act as possible capture centers. These solutions are f ound to exist in all external mean-motion resonances, for a wide range of values of the drag coefficient beta and planetary mass m1. The 1/2 , 2/3, and 1/3 commensurabilities are discussed in detail. Particular attention is given to the variation of the parameters of the libration solutions (position and stability) as functions of beta and m1. The a nalytical results are then compared with numerical simulations of the exact equations. Even though trappings are effectively found in these points, they are temporary: after a few 10(5)-10(6) years the particle suffers a close encounter with the perturber, resulting in an ejectio n from the resonance. Concerning the orbital evolution from the nonres onant initial conditions to the final librational orbit, we find the a veraged system to be adiabatic in general for m1 > 10(-3) beta. In thi s interval, the dissipative problem can be approximated by a slowly va rying one degree of freedom Hamiltonian system. We apply the formalism of the adiabatic invariant theory and discuss the mechanism and proba bility of capture in each resonance. Results are once again compared w ith numerical integrations. (C) 1994 Academic Press, Inc.