Strong Winds for Planetary Formation

by Holly Capelo

In our experiment in the Göttingen Dilute Gas Stream Facility GDGSF, we produce a 'wind' which contains very small spherical particles. The density of the wind is 1/100th the density of air at sea level.  The particles' sizes range from approximately 70 micrometres (the same as the thickness of a human hair) down to 20 micrometres (about half of the limit of what is visible to the unassisted human eye).  When the particles are trapped in the flow, we use high-resolution cameras to track their positions, to learn if and how the particles may swarm together in the flow and how the particles' group behaviour is different from the simple dynamics of individual particles. 

The spheres in the experiment are analogous to the small grains which are present in the dust- and gas- filled discs around young stars. In such environments, it is believed that particle-gas fluid instabilities, including the streaming instability, play a prominent role in the process of concentrating dust particles to assist in the formation of bigger objects like planetesimals, which are the precursors of planets.