Streaming instability in a swirling gas for laboratory planetary formation studies

The formation of kilometer-sized planetesimals from microscopic dust grains in a proto-planetary disk is an area of active research in astrophysics (Chiang & Youdin, AREPS, 2010). Streaming instability (SI), which arises from the drift of dust particles through a neutral gas, concentrates dust in regions of higher gas pressure, thereby facilitating dust accumulation (Youdin & Goodman, ApJ, 2005). Recent simulations have shown that SI is a leading candidate for planetesimal formation (Nesvorny et al, Nat Astron, 2019). However, there is a lack of observational support due to inherent difficulties in observing astrophysical objects of such small sizes. In this work, we aim to study SI in a controlled lab environment for the first time, using fog droplets as dust substitutes in a concentric cylindrical machine (Secunda et al, MNRAS, 2023). A fan is used to create a pressure gradient that draws the gas-fog mixture inward in a spiral motion. Due to incomplete coupling between gas and fog droplets, we expect the fog droplets to concentrate at "stalling radii" to bring the droplet-gas ratio to the SI threshold. Preliminary analysis shows that with sufficiently low turbulence, we expect SI to form with radial wavelengths on the order of mm with growth rates around 1000 s^−1. Although our system does not replicate the exact global conditions of a proto-planetary disk, we aim to investigate the evolution of SI, which is intrinsically a local process. Our experimental work will also be supported by N−body numerical simulations.