Effect of Incoming Solar Particle Radiations on The Exosphere of Mars
Abstract
Mars Exospheric Neutral Composition Analyzer (MENCA) of Mars Orbiter Mission (MOM) measures the in-situ neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by the presence of CO2 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 O2+ in the Martian ionosphere. Primary photo-dissociative species CO2, 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 ≈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 ≈160 km, under low solar activity conditions during June 2018. Observations of partial pressures of CO2 and O in subsequent orbits reveals that solar inputs are crucial in quantifying these crossing points, where [O]/[CO2] 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 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.