Impact Induced Atmosphere-Mantle Exchange Sets the Volatile Elemental Ratios on Primitive Earths

TL;DR

This study models how impact processes, atmosphere-mantle exchange, and accretion history influence volatile element ratios on Earth-like planets, revealing that these ratios are shaped by complex interactions during planet formation.

Contribution

It introduces a comprehensive volatile evolution model incorporating impact loss, atmosphere-mantle exchange, and dynamical accretion simulations to explain elemental ratio variations.

Findings

Most Earth-like planets develop superchondritic C/N ratios.

Volatile ratios are influenced by impact history and planetary properties.

Atmosphere-mantle exchange significantly alters elemental ratios during formation.

Abstract

Conventional planet formation theory suggests that chondritic materials have delivered crucial atmospheric and hydrospheric elements such as carbon (C), nitrogen (N), and hydrogen (H) onto primitive Earth. However, recent measurements highlight the significant elemental ratio discrepancies between terrestrial parent bodies and the supposed planet building blocks. Here we present a volatile evolution model during the assembly of Earth and Earth-like planets. Our model includes impact losses, atmosphere-mantle exchange, and time dependent effects of accretion and outgassing calculated from dynamical modeling outcomes. Exploring a wide range of planetesimal properties (i.e., size and composition) as well as impact history informed by N-body accretion simulations, we find that while the degree of CNH fractionation has inherent stochasticity, the evolution of C/N and C/H ratios can be traced back to certain properties of the protoplanet and projectiles. Interestingly, the majority of our Earth-like planets acquire superchondritic final C/N ratios, implying that the volatile elemental ratios on terrestrial planets are driven by the complex interplay between delivery, atmospheric ablation, and mantle degassing.