Solar wind-driven day-to-day effects on the Martian thermosphere/exosphere composition

TL;DR

This study reveals significant day-to-day variations in the Martian thermosphere/exosphere composition driven by solar wind effects, confirmed by MAVEN and MOM data, with implications for future atmospheric modeling and understanding solar cycle influences.

Contribution

It demonstrates the impact of solar wind plasma on Martian atmospheric constituents and provides first-time observational evidence of these effects during a specific period in 2018.

Findings

Argon density profiles vary significantly day-to-day despite stable solar EUV.

Electron impact dissociation and ionisation influence atmospheric composition during solar wind events.

Results inform future modeling of Martian atmosphere and solar cycle effects.

Abstract

Since the first \emph{in-situ} measurements of the altitude profile of upper atmospheric density and composition carried out by the Viking lander missions during 1976, similar data were continuously gathered by MAVEN and MOM spacecraft orbiting Mars since September 2014 with a mass spectrometer and other related payloads. Using near-simultaneous observations by the two orbiters, we show that both data sets confirm significant day-to-day variations of Argon ($Ar$) density profiles in the Martian thermosphere/exosphere during 1-15 June 2018 when the solar EUV radiation did not show any appreciable change. We extend this study to include the parent atmospheric constituents ($CO_{2}$, $Ar$, $He$, $N_{2}$) and the photochemical products ($O$, $CO$) to examine the effect of solar wind plasma ($e/H^{+}$) velocities and fluxes during the above time interval. Density profiles of these constituents show significant effects due to the additional electron impact dissociation and ionisation during the first week of June 2018, which subside in the next week returning to normal conditions. These first-time results are interpreted based on a number of relevant neutral and ion chemical reactions. This result provides a vital input to future modelling efforts of Martian thermosphere/exosphere composition studies and the solar EUV related variations due to the Schwabe cycle.