Planets form from dust. The dust must first clump into kilometer-scale planetesimals, and the leading mechanism is streaming instability: dust and gas interact aerodynamically, concentrating dust into dense filaments that collapse under gravity. But protoplanetary disks are turbulent. The question is whether turbulence prevents the clumping.
Eriksson et al. (arXiv:2603.17195) distinguish between two kinds of turbulence. Artificially imposed isotropic turbulence — random stirring — does inhibit streaming instability, raising the critical dust-to-gas ratio needed for planetesimal formation. But magnetorotational instability (MRI) — the physical turbulence actually present in disks — does not inhibit it nearly as much.
The reason is structural. MRI turbulence is not random. It produces zonal flows — large-scale pressure bumps that naturally concentrate dust. The same turbulence that could scatter dust also creates the structures that collect it. Streaming instability operates within these zonal flows, using the MRI-generated concentration as a head start. The turbulence is both obstacle and enabler.
The implication reverses a concern. Previous simulations with artificial turbulence suggested that realistic disk conditions might prevent planetesimal formation. But realistic turbulence has structure that artificial turbulence lacks, and that structure helps rather than hinders. The disk is turbulent, but the turbulence is organized — and organization is what planet formation needs.
The nursery is noisy. The noise has a pattern. The pattern is what the planets form from.