Disc and atmosphere composition of multi-planet systems

Abstract

In protoplanetary discs, small millimetre-centimetre-sized pebbles drift inwards which can aid in planetary growth and influence the chemical composition of their natal discs. Gaps in protoplanetary discs can hinder the effective inward transport of pebbles by trapping the material in pressure bumps. In this work, we explore how multiple planets change the vapour enrichment by gap opening. For this, we extended the code to include multiple growing planets and investigated the effect of 1, 2, and 3 planets on the water content and C/O ratio in the gas disc as well as the final composition of the planetary atmosphere. We followed planet migration over evaporation fronts and found that previously trapped pebbles evaporate relatively quickly and enrich the gas. We also found 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 previously trapped pebbles. Interestingly, we found 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.