Tracing water vapor and ice during dust growth

TL;DR

This study models dust coagulation, dynamics, and volatile processes in protoplanetary disks to understand how water vapor and ice distribution evolve near the snowline, revealing significant vapor depletion and shifts in the snowline position.

Contribution

It introduces a comprehensive model combining dust and volatile evolution, highlighting the impact of coagulation and turbulence on water vapor distribution in protoplanetary disks.

Findings

Water vapor can be depleted by up to 50 times in the disk atmosphere.

Vertical snowline moves closer to the midplane due to dust settling.

Gas-phase C/O ratio increases above the snowline.

Abstract

The processes that govern the evolution of dust and water (in the form of vapor or ice) in protoplanetary disks are intimately connected. We have developed a model that simulates dust coagulation, dust dynamics (settling, turbulent mixing), vapor diffusion, and condensation/sublimation of volatiles onto grains in a vertical column of a protoplanetary disk. We employ the model to study how dust growth and dynamics influence the vertical distribution of water vapor and water ice in the region just outside the radial snowline. Our main finding is that coagulation (boosted by the enhanced stickiness of icy grains) and the ensuing vertical settling of solids results in water vapor being depleted, but not totally removed, from the region above the snowline on a timescale commensurate with the vertical turbulent mixing timescale. Depending on the strength of the turbulence and the temperature, the depletion can reach factors of up to ${\sim}50$ in the disk atmosphere. In our isothermal column, this vapor depletion results in the vertical snowline moving closer to the midplane (by up to 2 gas scale heights) and the gas-phase C/O ratio above the vertical snowline increasing. Our findings illustrate the importance of dynamical effects and the need for understanding coevolutionary dynamics of gas and solids in planet-forming environments.