  Since the first in-situ measurements of the altitude profile of upper
atmospheric density and composition were carried out by the Viking lander
missions in 1976, similar data are continuously gathered by MAVEN and MOM
spacecraft orbiting Mars since their launch in September 2014 with mass
spectrometers and other related payloads. Using near-simultaneous observations
by the two orbiters, it is seen that both data sets indicate significant
day-to-day variations of Argon density profiles in the thermosphere-exosphere,
150-300 km region, during the period 1-15, June 2018, when the solar EUV
radiation did not show any appreciable change but the solar wind energetic
particle fluxes did so. Extending this study to include the other parent
atmospheric constituents carbon dioxide, helium, nitrogen and their
photochemical products atomic oxygen, and carbon monoxide during the same
period it is found that the density profiles of carbon dioxide and atomic
oxygen also show similar variations with carbon dioxide densities showing an
increasing trend similar to Argon, but a reversal of this trend for atomic
oxygen densities. Using insitu and near simultaneous measurements of solar EUV
fluxes and the solar wind plasma velocities and densities near MAVEN periapsis
it is noted that, unlike the solar EUV radiation, solar wind parameters showed
a decrease by a factor of 2-3. Hence, it is inferred that the energetic and
penetrating solar wind charged particle impact-driven dissociation, ionisation
and ion-chemical processes could decrease the carbon dioxide densities leading
to an increase in atomic oxygen densities. This result is also discussed from
the considerations of the proton gyro radius effect, pickup ions, sputtering,
energetic neutral atoms driven ionisation and ion losses. Further data and
modelling efforts would be necessary to confirm this finding.
