Aims. Dust-plasma interaction may play a dominant role in the dynamics of dust particles around young main-sequence stars. Circumstellar dust is expected to be an aggregate consisting of small grains. The momentum transfer cross section (MTCS) for an aggregate is a key quantity for determining the lifetimes of circumstellar dust disks. Methods. We formulate the MTCS of fluffy dust aggregates and propose an algorithm for computing the MTCS. We compare the magnitude of the plasma and photon Poynting-Roberson effects (PR effects). Results. We find an empirical formula that approximates numerical results well for the MTCSs. A comparison of the magnitudes of the PR effects shows that the lifetime of debris dust around young main-sequence stars is shorter by orders of magnitude than the lifetime estimated by considering the photon PR effect alone. Brief discussion is given on the plasma PR effect for dust debris disks around young main-sequence stars.

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Abstract. Solar-wind particles striking dust grains in orbit around the sun exert not only a repulsive force on the grains, but also a drag force, called the plasma or pseudo Poynting-Robertson (PR) effect, which limits their dynamical lifetimes. To better understand the dynamical evolution of interplanetary dust, we study the momentum transfer from the solar wind to interplanetary dust taking into account the passage of impinging particles through the grains. The pseudo PR drag is one of the most important perturbations for the dynamics of interplanetary dust of any sizes. However, previous studies underestimated the lifetimes of small grains by overestimating the acting solar-wind forces. Our study also provides the velocity distribution of neutralized solar-wind particles after passage through a grain along with some implications for the generation of pick-up ions by solar-wind interaction with dust grains.

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