Oral Presentation

Dust Diffusion as a Driver of Planetesimal Formation: Instabilities, Efficiencies, and Neural Models

Author(s): Konstantin Gerbig (University of Chicago)

Presenter: Konstantin Gerbig (University of Chicago)

Dust diffusion is often treated as a passive smoothing process in protoplanetary disks—but it is in fact a key driver of planetesimal formation. In this talk, I argue that understanding how diffusion depends on local disk conditions is essential for explaining when, where, and how solids collapse into planetesimals. I first show that dust diffusion can destabilize the dust disk: when the effective diffusivity decreases with increasing dust density, a diffusive instability emerges that produces radially separated, high-density filaments. This mechanism offers a new route to strong particle concentration, potentially occurring after the streaming instability has saturated. I then present a data-driven approach based on neural differential equations, trained on high-resolution simulations of streaming turbulence, to learn effective closures for dust transport. This framework reveals how turbulent diffusion varies with local dust properties and provides a systematic way to model regimes where standard prescriptions break down. Finally, I discuss the efficiency of planetesimal formation via the streaming instability, highlighting how diffusion regulates the fraction of solids that ultimately collapse into bound objects. Together, these results recast diffusion as an active control parameter in planetesimal formation, shaping both the emergence of dense substructure and the efficiency of collapse.