Solar wind and motion of dust grains

Action of solar wind on arbitrarily shaped interplanetary dust particle is investigated. The final relativistically covariant equation of motion of the particle contains both orbital evolution and change of particle’s mass. Non-radial solar wind velocity vector is also included. The covariant equation of motion reduces to the Poynting-Robertson effect in the limiting case when spherical particle is treated, the speed of the incident solar wind corpuscles tends to the speed of light and the corpuscles spread radially from the Sun. The results of quantum mechanics have to be incorporated into the physical considerations, in order to obtain the limiting case. The condition for the solar wind effect on motion of spherical interplanetary dust particle is p′out = ( 1 − σ′ pr/σ ′ tot ) p ′ in, where p ′ in and p ′ out are incoming and outgoing radiation momenta (per unit time) measured in the proper frame of reference of the particle; σ′ pr and σ ′ tot are solar wind pressure and total scattering cross sections. Analytical solution of the derived equation of motion yields qualitative behaviour consistent with numerical calculation. This holds also if decrease of particle’s mass is important, when also outspiralling from the Sun may occur. Real flux density of radial solar wind energy yields that the time of spiralling toward the Sun may differ in about 10 % from the case of constant flux for heliocentric distances smaller than about 10 AU (if radius of the particle is unchaged). The differences between the real solar wind effect (when also non-radial solar wind velocity vector is taken into account) and the standard approach may be even more significant for heliocentric distances greater than 10 AU: solar wind can cause outspiralling from the Sun, even if radius of the particle is constant. Real flux density of solar wind energy produces shift of perihelion of interplanetary dust particles. This result significantly differs from the standard treatment of the action of the solar wind on dust particles, when analogy with the Poynting-Robertson effect is stressed. Moreover, the evolution of the shift of perihelion depends on orbital position of the parent body at the time of ejection of the particle.