Variation of nongravitational parameters of comet Encke as a result of its decay

Existing models for nongravitational effects in cometary motion are reviewed. Marsden's model is the most extensively used for linkage of few successive apparitions. For linkage of numerous apparitions, there is not any unified method yet. Various modifications of Marsden's model were developed explaining the variation of nongravitational parameters mainly through the precession of the cometary nucleus rotation axis and the outgassing from discrete surface sources. However, the mass loss and the shrinking of the sublimating area were not considered. The construction of the theory of motion for comet Encke presents particular difficulties. In the present paper, it is shown that the variation of the nongravitational parameters of comet Encke may be qualitatively explained by self-consistent models of the mass loss without reference to a hypothesis of the nucleus rotation axis precession.