Speaker: Dr. Marius Lehmann, Iowa State University

Host: Charles Kerton

Title: Impact of hydrodynamic instabilities on planet formation and migration in protoplanetary disks

Abstract: Planet formation in protoplanetary disks begins with the coagulation of dust into macroscopic pebbles. Through dust-gas drag mechanisms like the streaming instability, these pebbles concentrate into dense clumps that gravitationally collapse into planetesimals, eventually growing into the diverse planetary architectures we observe today, ranging from terrestrial worlds to massive gas giants.
Concurrently, nascent planets interact with their host disk, driving radial migration that typically proceeds inward. A crucial theoretical challenge is identifying the mechanisms required to stall this drift—particularly for low-mass planets up to a few Earth masses—before they are lost to their host stars before we can detect them. Thus, the initial assembly of planetesimals and the subsequent survival of migrating planets represent equally critical, closely linked hurdles in formation theory.
However, models of these stages often reduce complex dust-gas dynamics and turbulence to the standard alpha-viscosity prescription. In these parameterized models, viscosity acts as a critical limiting factor—actively opposing particle concentration during formation while driving the viscous disk evolution and gravitational torques that govern planetary migration.
In this talk, I will discuss the impact of explicitly modeled hydrodynamic instabilities as a prominent source of turbulence. By modeling these instabilities explicitly rather than relying on an alpha-parameter to capture specific fluid flow structures, I will explore how these dynamic environments fundamentally alter our understanding of both the efficiency of initial planetesimal formation and the subsequent orbital survival of low-mass planets.

Bio: Dr. Marius Lehmann is a Postdoctoral Research Associate at Iowa State University. Prior to joining the university in September 2025, he earned his PhD in Astronomy from the University of Oulu in Finland and completed a postdoctoral fellowship at ASIAA in Taiwan. He works on global MHD simulations of planet-forming disks, with the aim of making direct connections between observables of processes like magnetically-driven turbulence and magnetically-launched outflows and winds. Marius is also working on various hydrodynamic instabilities in planet-forming disks and their effect on dust concentration and planet migration. Alongside his research, he actively mentors undergraduate students on studies of planetesimal formation in turbulent environments.