Curveballs in protoplanetary disks - the effect of the Magnus force on planet formation

TL;DR

This paper investigates how the Magnus force affects the dynamics of spinning planetesimals in protoplanetary disks, revealing it can extend their lifetime and influence planetesimal formation processes.

Contribution

It introduces the effect of the Magnus force into planetesimal dynamics, showing its potential to prolong solid lifetimes and hinder gravitational instability-based planetesimal formation.

Findings

Magnus force can extend the lifetime of meter-sized boulders in disks.

The force can prevent planetesimal formation via gravitational instability for particles larger than ~10 cm.

Streaming instability modes may still grow despite the Magnus force's diffusive effects.

Abstract

Spinning planetesimals in a gaseous protoplanetary disk may experience a hydrodynamical force perpendicular to their relative velocities. We examine the effect this force has on the dynamics of these objects using analytical arguments based on a simple laminar disk model and numerical integrations of the equations of motion for individual grains. We focus in particular on meter-sized boulders traditionally expected to spiral in to the central star in as little as 100 years from 1 A.U. We find that there are plausible scenarios in which this force extends the lifetime of these solids in the disk by a factor of several. More importantly the velocities induced by the Magnus force can prevent the formation of planetesimals via gravitational instability in the inner disk if the size of the dust particles is larger than of order 10 cm. We find that the fastest growing linear modes of the streaming instability may still grow despite the diffusive effect of the Magnus force, but it remains to be seen how the Magnus force will alter the non-linear evolution of these instabilities.