Disk and atmosphere composition of multi-planet systems

TL;DR

This study investigates how multiple planets in protoplanetary disks influence the chemical composition of the disk and planetary atmospheres, focusing on water content, C/O ratio, and nitrogen enrichment due to pebble drift and evaporation.

Contribution

It extends the chemcomp code to model multiple growing planets and analyzes their impact on disk chemistry and planetary atmospheres, revealing new effects of planet multiplicity on volatile distribution.

Findings

Multiple planets reduce atmospheric carbon and oxygen compared to single-planet systems.

Trapped pebbles evaporate quickly when not blocked, enriching the gas.

Nitrogen remains super-stellar, indicating pebble drift's role in atmospheric composition.

Abstract

In protoplanetary disks, small mm-cm-sized pebbles drift inwards which can aid planetary growth and influence the chemical composition of their natal disks. Gaps in protoplanetary disks can hinder the effective inward transport of pebbles by trapping the material in pressure bumps. Here we explore how multiple planets change the vapour enrichment by gap opening. For this, we extend the chemcomp code to include multiple growing planets and investigate the effect of 1, 2 & 3 planets on the water content and C/O ratio in the gas disk as well as the final composition of the planetary atmosphere. We follow planet migration over evaporation fronts and find that previously trapped pebbles evaporate relatively quickly and enrich the gas. We also find that in a multi-planet system, the atmosphere composition can be reduced in carbon and oxygen compared to the case without other planets, due to the blocking of volatile-rich pebbles by an outer planet. This effect is stronger for lower viscosities because planets migrate further at higher viscosities and eventually cross inner evaporation fronts, releasing the previously trapped pebbles. Interestingly, we find that nitrogen remains super-stellar regardless of the number of planets in the system such that super-stellar values in N/H of giant planet atmospheres may be a tracer for the importance of pebble drift and evaporation.