Sunday, October 19, 2014

How Planetesimals Munch Dust

On the filtering and processing of dust by planetesimals 1. Derivation of collision probabilities for non-drifting planetesimals


Guillot et al



Circumstellar disks are known to contain a significant mass in dust ranging from micron to centimeter size. Meteorites are evidence that individual grains of those sizes were collected and assembled into planetesimals in the young Solar System. Aims. We assess the efficiency of dust collection of a swarm of planetesimals with radii ranging from 1 to 10^3 km and beyond.


We derive analytical expressions of the probability for drifting dust to collide with planetesimals.


For standard turbulence conditions (i.e. a turbulence parameter {\alpha} = 10^-2), filtering is found to be inefficient, meaning that when crossing a minimum-mass solar nebula belt of planetesimals extending between 0.1 and 35 AU most dust particles are eventually accreted by the central star. However, if the disk is weakly turbulent ({\alpha} = 10^-4) filtering becomes efficient in two regimes: (i) For planetesimals smaller than about 10km in size and dust of all sizes and (ii) for planetary embryos larger than about 1000km in size and dust of millimeter-size or larger. The first regime strongly favors short orbital distances while the second only weakly depends on orbital distance. Dust particles much smaller than millimeter-size tend to be only captured by the smallest planetesimals.

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