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Making planetesimals in turbulent disks is not easy

Image Credit: Chen & Lin (2020, ApJ, 891, 132)

The "streaming instability" (SI) in a physical protoplanetary disk model.

The streaming instability (SI) is the leading theory for planetesimal formation - the building blocks of planets. Does it work in practice? The red curve show growth timescales of the SI in a physically-motivated disk model. The black curve show the inward drift timescales of dust particles. This particular disk model assumes a high dust-to-gas mass ratio of 0.1 and consider cm-sized dust grains. From previous studies that do not consider turbulence, these conditions should favor the SI. However, in more realistic disk models we find long growth timescales inside ~40AU, where dust will be lost before the SI can grow significantly. On the other hand, at larger radii (>40AU) the SI can grow before dust is lost. Our results indicates that the SI, and hence planetesimal formation, is limited to the outer disk. This work was lead by Kan Chen, an alumnus from the ASIAA Summer Student Program.