Wind-driven Exclusion of Cosmic Rays in the Protoplanetary Disk Environment

TL;DR

This paper models how stellar winds create heliosphere-like regions that exclude cosmic rays from protoplanetary disks, impacting disk chemistry and turbulence, with implications for planet formation.

Contribution

It introduces models of cosmic ray exclusion by stellar winds in protoplanetary environments and discusses observational strategies to detect such regions.

Findings

CR exclusion reduces ionization rates in disks by orders of magnitude

CR exclusion influences disk turbulence and chemical composition

ALMA can potentially detect stellar heliosphere analogs around young stars

Abstract

The recent (apparent) passage of the Voyager 1 spacecraft into interstellar space provides us with front-row seats to the complex interplay between the solar wind and the protective surrounding bubble known as heliosphere. The heliosphere extends radially out to $\sim100$ AU from the sun, and within this sphere of influence, the solar wind modulates the incoming flux of galactic cosmic rays (CRs), especially those at low energies. Newly formed stars, which support both strong magnetic fields and winds, are expected to produce analogous regions of CR exclusion, perhaps at elevated levels. Such young stars are encircled by molecular gas-rich disks, and the net removal of CRs from the circumstellar environment significantly reduces the expected CR ionization rate in the disk gas, most likely by many orders-of-magnitude. The loss of ionization reduces disk turbulence, and thereby affects both planet-formation and active chemical processes in the disk. We present models of CR exclusion and explore the implications for turbulence and for predicted chemical abundances. We also discuss means by which ALMA can be used to search for extrasolar heliosphere-analogs around young stars.