Nongravitational Forces on Comets: An Extension of the Standard Model

The accuracy of comet orbit computations is limited by uncertain knowledge of the recoil force due to outgassing from the nuclei. The standard model assumes an exponential dependence of the force on distance from the Sun. This variable force times constants A 1 , A 2 , and A 3 represents the radial, transverse, and normal components of the net force. Orbit solutions show that the A s often vary considerably over a few apparitions of the comets. In this paper, we allow for time variations of the A s, and we show that for several comets this improves the orbit accuracy considerably.