Effect of Incoming Solar Particle Radiations on The Exosphere of Mars

TL;DR

This study presents the first direct in-situ observations of how energetic solar particle radiation influences the composition and dynamics of Mars's exosphere, highlighting the role of solar activity in atmospheric crossover processes.

Contribution

It provides new in-situ measurements of Martian exospheric neutral species under varying solar conditions, revealing the impact of solar energetic particles on atmospheric composition and escape processes.

Findings

Solar inputs influence the crossover altitude of atomic O and CO2.

Solar wind charged particles affect exospheric composition during evening hours.

First in-situ observation of solar energetic particles impacting Mars's exosphere.

Abstract

Mars Exospheric Neutral Composition Analyzer (MENCA) of Mars Orbiter Mission (MOM) measures the \emph{in-situ} neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by the presence of $CO_2$ which photo-dissociates into atomic oxygen ($O$) in higher altitudes much near the exobase. Atomic $O$ plays a significant role in invoking the stronger presence of $O_2^+$ in the Martian ionosphere. Primary photo-dissociative species $CO_{2}$, crossover their neutral abundance with atomic $O$ in the collisionless heterogenous atmosphere with varying local solar conditions. Initial measurements from Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument on Mars Atmosphere and Volatile Evolution (MAVEN) estimated these crossover/transition altitudes wavering between $\approx$225 km to 240 km during solar maximum conditions with peak solar illuminations. MENCA sampled the neutral atmospheric species, below the exobase up to the periareion of $\approx$160 km, under low solar activity conditions during June 2018. Observations of partial pressures of $CO_2$ and $O$ in subsequent orbits reveals that solar inputs are crucial in quantifying these crossing points, where $[O]/[CO_2]$ remain unity, alongside the influences from temperature. The multi-spacecraft measurements of the direct influences of solar wind charged particle fluxes and velocity on the daily variation of neutral thermospheric/exospheric compositions were observed on the local evening hours of Mars and presented. It marks the first-ever direct \emph{in-situ} observation of interaction between the energetic solar particle radiations on Martian exospheric compositions, potentially contributing to the steady escape and differing population of atomic $[O]$ in the exosphere.