Impact regimes and post-formation sequestration processes: implications for the origin of heavy noble gases in terrestrial planets

TL;DR

This study investigates the variation of heavy noble gases in Venus, Earth, and Mars, proposing cometary bombardment and clathrate sequestration as key processes influencing their atmospheric compositions.

Contribution

It provides a quantitative explanation for noble gas abundance differences using dynamical simulations and introduces the role of Martian clathrates in noble gas sequestration.

Findings

Cometary impacts can account for noble gas levels on Venus and Earth.

Martian clathrates likely sequestered significant noble gases.

Impact fluxes correlate with observed atmospheric compositions.

Abstract

The difference between the measured atmospheric abundances of neon, argon, krypton and xenon for Venus, the Earth and Mars is striking. Because these abundances drop by at least two orders of magnitude as one moves outward from Venus to Mars, the study of the origin of this discrepancy is a key issue that must be explained if we are to fully understand the different delivery mechanisms of the volatiles accreted by the terrestrial planets. In this work, we aim to investigate whether it is possible to quantitatively explain the variation of the heavy noble gas abundances measured on Venus, the Earth and Mars, assuming that cometary bombardment was the main delivery mechanism of these noble gases to the terrestrial planets. To do so, we use recent dynamical simulations that allow the study of the impact fluxes of comets upon the terrestrial planets during the course of their formation and evolution. Assuming that the mass of noble gases delivered by comets is proportional to rate at which they collide with the terrestrial planets, we show that the krypton and xenon abundances in Venus and the Earth can be explained in a manner consistent with the hypothesis of cometary bombardment. In order to explain the krypton and xenon abundance differences between the Earth and Mars, we need to invoke the presence of large amounts of CO2-dominated clathrates in the Martian soil that would have efficiently sequestered these noble gases.