MOTION OF DUST PARTICLES UNDER THE INFLUENCE OF A LATITUDINALLY DEPENDENT FORCE

The Kelperian motion of dust particles in the solar system is mainly i nfluenced by the electromagnetic and plasma Poynting-Robertson drag. T he first force is isotropic while the second one shows latitudinal var iations due to the observed differences of the solar wind parameters i n the ecliptic plane and over the solar poles. Close to the Sun other effects become important, e.g. sublimation and sputtering, as well as for submicron particles Lorentz scattering has to be taken into accoun t. These forces are very weak for dust grains of moderate size (10-100 mu) not too close (> 0.03 AU) to the Sun and are neglected here. Assu ming that the general form of the latidudinally dependent force is a s eries expansion in Legendre polynomials, we have studied the averaged equations of motion for the classical elements and found the first int egral of them. The general character of motion is the same as for the classical Poynting-Robertson drag: particles spiral towards the Sun. T he new features in the orbital evolution under the latitudinally depen dent force as compared with the isotropic Poynting-Robertson drag are: (1) not only the semimajor axis a and the eccentricity epsilon but al so the argument of the perihelion omega varies with time, (2) the rate of change of a, epsilon, omega depends on the inclination. An example of particle trajectories in the phase space of elements is presented.