Solar wind dominance over the Poynting-Robertson effect in secular orbital evolution of dust particles

Abstract

Properties of the solar wind are discussed and applied to the effect of the wind on motion of bodies in the Solar System. The velocity density function for the solar wind constituents is given by the $\kappa-$distribution. The relevant contributions to the solar wind action contain also the sputtering and reflection components in addition to direct impact. The solar wind effect is more important than the action of the solar electromagnetic radiation, as for the secular orbital evolution. The effect of the solar corpuscular radiation is more important than the Poynting-Robertson effect even when mass of the dust particle is considered to be constant, non-radial component of the solar wind velocity is neglected and the time dependence of the solar wind properties is ignored. The presented equation of motion of a body under the action of the solar radiation, electromagnetic and corpuscular, respects reality in a much better way than the conventionally used equation. The acceleration of the body is proportional to the superposition of the radial velocity component multiplied by the numerical coefficient $[2 + (\eta_{1} + \eta_{2})/ \overline{Q} ~'_{pr}]$ and the transversal velocity component multiplied by the numerical coefficient $(1 + \eta_{2}/ \overline{Q} ~'_{pr})$, where $\overline{Q} ~'_{pr}$ is the dimensionless efficiency factor of the radiation pressure. Here $\eta_{1}$ $\doteq$ 1.1, $\eta_{2}$ $\doteq$ 1.4 and the velocity is the body's velocity with respect to the Sun. Also time variability of $\eta_{1}$ and $\eta_{2}$ due to the solar cycle is given. The dimensionless cross section the dust grain presents to wind pressure is about 4.7. This value differs from the conventionally used value 1.0. The mass-loss rate of the zodiacal cloud is 4-times higher than the currently accepted value, as for the micron-sized dust particles.