Experimentelle und Analytische Planetologie
Drag Forces on Dust in the Solar System and in Circumstellar Systems
Radiation pressure force diminishes the gravitational force acting on dust grains in circumstellar disks and in the
solar system. Dust particles exposed to high radiation pressure are ejected from the circumstellar disk while
grains at low radiation pressure stay in bound orbits around the central star. The lifetime of dust in orbital
motion about the Sun or about a central star is furthermore limited by the electromagnetic Poynting-Robertson
effect due to the component of the radiation pressure force directed against the velocity of the moving particle.
Aside from solar radiation, impacting solar wind particles exert a force on the dust grains. Its tangential
component acts in a similar way and is therefore referred to as plasma Poynting-Robertson effect. The
electromagnetic Poynting-Robertson force is proportional to vd/c, where vd is the
tangential component of the dust orbital velocity and c is the speed of light, while the plasma
Poynting-Robertson force is proportional to vd/ vSW, where vSW is
the solar wind velocity. Since vSW c the plasma Poynting-Robertson effect is comparable to the
electromagnetic Poynting-Robertson effect although the direct radiation pressure exceeds the direct solar wind
pressure. Both the radiation forces and solar wind forces depend on the grain properties such as material, size,
and structure. Therefore estimates of the dust lifetime require detailed consideration of these quantities.
We
calculated the influence of radiation pressure force on compact, spherical grains, porous, spherical grains and
aggregate particles consisting of silicate and carbon. The influence of radiation pressure force increases with
the increasing porosity of the particles. Our simulations of the plasma drag show that for small particles sizes
the plasma Poynting-Robertson effect becomes increasingly important compared to the electromagnetic
Poynting-Robertson effect.
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