Hot oxygen and carbon escape from the martian atmosphere

TL;DR

This study models hot oxygen and carbon escape from Mars' atmosphere, revealing how solar activity influences loss rates and highlighting the importance of collisional effects above the exobase.

Contribution

It introduces a detailed Monte-Carlo model including collision dynamics and energy distributions to quantify atmospheric escape rates on Mars.

Findings

Hot oxygen loss rate is 2.3-2.9×10^{25} s^{-1} during different solar conditions.

Carbon loss rate varies from 0.8 to 3.2×10^{24} s^{-1} with solar activity.

Collisional effects reduce escape rates by 20-30%.

Abstract

The escape of hot O and C atoms from the present martian atmosphere during low and high solar activity conditions has been studied with a Monte-Carlo model. The model includes the initial energy distribution of hot atoms, elastic, inelastic, and quenching collisions between the suprathermal atoms and the ambient cooler neutral atmosphere, and applies energy dependent total and differential cross sections for the determination of the collision probability and the scattering angles. The results yield a total loss rate of hot oxygen of $2.3-2.9\times 10^{25}\,{\rm s}^{-1}$ during low and high solar activity conditions and is mainly due to dissociative recombination of O$_2^+$ and CO$_2^+$. The total loss rates of carbon are found to be $0.8$ and $3.2\times 10^{24}\,{\rm s}^{-1}$ for low and high solar activity, respectively, with photodissociation of CO being the main source. Depending on solar activity, the obtained carbon loss rates are up to $\sim 40$ times higher than the CO$_2^+$ ion loss rate inferred from Mars Express ASPERA-3 observations. Finally, collisional effects above the exobase reduce the escape rates by about $20-30\,\%$ with respect to a collionless exophere.