C/O and Snowline Locations in Protoplanetary Disks: The Effect of Radial Drift and Viscous Gas Accretion

TL;DR

This study investigates how radial drift of solids and viscous gas accretion influence the locations of snowlines of key volatiles in protoplanetary disks, affecting the disk's C/O ratio and planetary formation conditions.

Contribution

It provides new insights into how radial drift and viscous accretion alter snowline positions for water, CO2, and CO in different disk models, refining previous static disk assumptions.

Findings

Radial drift and accretion move snowlines inward by up to 60%.

Snowline location depends on particle size, not initial position.

Inner limits of snowline positions are established considering dynamic effects.

Abstract

The C/O ratio is a defining feature of both gas giant atmospheric and protoplanetary disk chemistry. In disks, the C/O ratio is regulated by the presence of snowlines of major volatiles at different distances from the central star. We explore the effect of radial drift of solids and viscous gas accretion onto the central star on the snowline locations of the main C and O carriers in a protoplanetary disk, H2O, CO2 and CO, and their consequences for the C/O ratio in gas and dust throughout the disk. We determine the snowline locations for a range of fixed initial particle sizes and disk types. For our fiducial disk model, we find that grains with sizes ~0.5 cm < s < 7 m for an irradiated disk, and ~0.001 cm < s < 7 m for an evolving and viscous disk, desorb at a size-dependent location in the disk, which is independent of the particle's initial position. The snowline radius decreases for larger particles, up to sizes of ~7 m. Compared to a static disk, we find that radial drift and gas accretion in a viscous disk move the H2O snowline inwards by up to 40%, the CO2 snowline by up to 60%, and the CO snowline by up to 50%. We thus determine an inner limit on the snowline locations when radial drift and gas accretion are accounted for.