Early Planet Formation: A Facility to Study the Time Evolution and Equilibrium States of Multitudes of Interacting sub-millimeter to centimeter Dust and Ice Aggregate Ensembles

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Planetary formation takes place in accretion disks (protoplanetary disks) around newly formed stars. The early phase is dominated by collisional growth of dust and ice aggregates: The initially micron sized dust and ice particles collide, stick together by surface forces and form larger aggregates which are the seeds for further growth. Up to millimeter size collisions are dominated by sticky interactions. However, the outcome of collision of sub-mm to mm/cm sized dust and ice aggregates is till this date unclear, even a emph(boucing barrier) is postulated for the typical collision velocities in a disk of mm/s to cm/s. This might prevent further growth (no more sticking) or might also be beneficial (sweep-up of the small aggregates by larger bodies). Hence, the intermediate stage of planet formation is not sufficiently understood.It was recently discovered that free collisions of sub-mm to several cm dust and ice aggregates within the mm/s to cm/s regime can be realized in the laboratory by levitating aggregates over a surface by a Knudsen compressor effect. Collisions between the levitating dust and ice aggregates with mm/s to cm/s are frequently (several per second) observable and probabilities for sticking, bouncing and fragmentation and their details can be gained over unlimited periods of time. Hence, the details of single collisions and espacially the time evolution towards equilibrium states of a system of multitudes of interacting dust or ice aggregates are experimental accessible.At the inner edge and at the optically thin parts of protoplanetary disks dust aggregates are irradiated by the host star. It was also just recently discovered that aggregates are subject to a photophoretic force which accelerates the dust. Having multitudes of free levitating aggregates in the laboratory, studies of photophoresis are possible.In this project we carry out collision experiments in the laboratory with and without the influence of photophoresis: The time evolution of thousands of free interacting sub-mm to cm dust and ice aggregates is easily accessible in the laboratory for the first time which will be studied in detail here.