The distribution of heavy-elements in giant protoplanetary atmospheres: the importance of planetesimal-envelope interactions

Abstract: In the standard model for giant planet formation, the planetary growth begins with accretion of solids followed by a buildup of a gaseous atmosphere as more solids are accreted, and finally, by rapid accretion of gas. The interaction of the solids with the gaseous envelope determines the subsequent planetary growth and the final internal structure. In this work we simulate the interaction of planetesimals with a growing giant planet (proto-Jupiter) and investigate how different treatments of the planetesimal-envelope interaction affect the heavy-element distribution, and the inferred core mass. We consider various planetesimal sizes and compositions as well as different ablation and radiation efficiencies, and fragmentation models. We find that in most cases the core reaches a maximum mass of 2 Earth's Mass. We show that the value of the core's mass mainly depends on the assumed size and composition of the solids, while the heavy-element distribution is also affected by the fate of the accreted planetesimals (ablation/fragmentation). Fragmentation, which is found to be important for planetesimals > 1 km, typically leads to enrichment of the inner part of the envelope while ablation results in enrichment of the outer atmosphere. Finally, we present a semi-analytical prescription for deriving the heavy-element distribution in giant protoplanets.