Photophoresis of dust aggregates in protoplanetary disks

Technische Universität Braunschweig, Institut für Geophysik und extraterrestrische Physik, Mendelssohnstraße 3, 38106 Braunschweig, Germany
e-mail: i.vonborstel@tu-bs.de

Received: 16 May 2012
Accepted: 28 September 2012

Abstract

Aims. Photophoretic motion of dust agglomerates can play a role for the re-distribution and mixing of material in protoplanetary disks. The dust agglomerates can consist of various materials and may possess a variety of morphologies and sizes. This experimental study intends to investigate the influence of different dust materials and dust aggregate sizes on the photophoretic motion.

Methods. Dust agglomerates were subjected to different light intensities and their respective photophoretic motion was observed under microgravity conditions and in a rarefied gas.

Results. The measured velocities for dust aggregates are on average proportional to the size of the dust aggregate, vary largely with material, and for a given material the velocity distribution for a single dust aggregate size is very broad and can be described by a Gaussian with a width comparable to its mean velocity. Remarkably, a fraction of a few 10 percent of all particles investigated exhibit a motion in the opposite direction. The mean photophoretic velocity of dust aggregates can be explained by the model of Beresnev et al. (1993, Phys. Fluids, 5, 2043) with a surprisingly high value for the ratio of heat conductivity to the asymetry factor of λ/J₁   0.1 W/m/K. Earlier work on photophoretic particle transport in protoplanetary disks assumed values of λ/J₁   0.001 W/m/K so that the real transport efficiency should me much lower and the corresponding timescale much longer.