  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.
