Chemical Evolution in a Protoplanetary Disk within Planet Carved Gaps and Dust Rings

TL;DR

This study investigates how dust rings and gaps in protoplanetary disks influence local chemistry, revealing temperature-driven volatile sublimation and freeze-out processes that affect planet formation environments.

Contribution

The paper introduces a thermochemical model of chemical evolution within disk substructures, highlighting the impact of dust temperature variations on volatile distribution and sublimation in gaps and rings.

Findings

Dust temperature increases in gaps cause volatile sublimation.

Dust-rich rings act as freeze-out traps for volatiles.

Line emission depends on gap depth, location, and gas tracer abundance.

Abstract

Recent surveys of protoplanetary disks show that substructure in dust thermal continuum emission maps is common in protoplanetary disks. These substructures, most prominently rings and gaps, shape and change the chemical and physical conditions of the disk, along with the dust size distributions. In this work, we use a thermochemical code to focus on the chemical evolution that is occurring within the gas-depleted gap and the dust-rich ring often observed behind it. The composition of these spatial locations are of great import, as the gas and ice-coated grains will end up being part of the atmospheres of gas giants and/or the seeds of rocky planets. Our models show that the dust temperature at the midplane of the gap increases, enough to produce local sublimation of key volatiles and pushing the molecular layer closer to the midplane, while it decreases in the dust-rich ring, causing a higher volatile deposition onto the dust grain surfaces. Further, the ring itself presents a freeze-out trap for volatiles in local flows powered by forming planets, becoming a site of localized volatile enhancement. Within the gas depleted gap, the line emission depends on several different parameters, such as: the depth of the gap in surface density, the location of the dust substructure, and the abundance of common gas tracers, such as CO. In order to break this uncertainty between abundance and surface density, other methods such as disk kinematics, become necessary to constrain the disk structure and its chemical evolution.