The Effect of Inefficient Accretion on Planetary Differentiation

TL;DR

This study compares perfect merging and neural network-based collision models in planetary formation simulations, revealing that realistic, inefficient accretion leads to greater compositional diversity in terrestrial planets, especially smaller ones.

Contribution

Introduces a neural network-based collision model for more realistic planetary accretion simulations, highlighting its impact on planetary composition diversity.

Findings

Neural network model predicts wider range of core mass fractions.

Inefficient accretion increases compositional diversity in small planets.

Results suggest realistic collision modeling is crucial for understanding planetary diversity.

Abstract

Pairwise collisions between terrestrial embryos are the dominant means of accretion during the last stage of planet formation. Hence, their realistic treatment in N-body studies is critical to accurately model the formation of terrestrial planets and to develop interpretations of telescopic and spacecraft observations. In this work, we compare the effects of two collision prescriptions on the core-mantle differentiation of terrestrial planets: a model in which collisions are always completely accretionary (``perfect merging'') and a more realistic model based on neural networks that has been trained on hydrodynamical simulations of giant impacts. The latter model is able to predict the loss of mass due to imperfect accretion and the evolution of non-accreted projectiles in hit-and-run collisions. We find that the results of the neural-network model feature a wider range of final core mass fractions and metal-silicate equilibration pressures, temperatures, and oxygen fugacities than the assumption of perfect merging. When used to model collisions in N-body studies of terrestrial planet formation, the two models provide similar answers for planets more massive than 0.1 Earth's masses. For less massive final bodies, however, the inefficient-accretion model predicts a higher degree of compositional diversity. This phenomenon is not reflected in planet formation models of the solar system that use perfect merging to determine collisional outcomes. Our findings confirm the role of giant impacts as important drivers of planetary diversity and encourage a realistic implementation of inefficient accretion in future accretion studies.