Photophoresis on polydisperse basalt microparticles under microgravity.

Photophoresis is a force which can dominate the motion of illuminated aerosols in low pressure environments of laboratory experiments, planetary atmospheres or protoplanetary disks. In drop tower experiments we quantified the photophoretic force on a sample of micrometer-sized basalt grains and aggregates thereof. The particle motions are systematic (linear, helical, in one direction), with most particles moving along the direction of light. Our results are consistent with analytical estimates and numerical simulations of photophoretic forces for small dust aggregates. It implies that the forces are dominated by Δ T - photophoresis with little evidence for Δ α - photophoresis in the micrometer size range. [ABSTRACT FROM AUTHOR]