Effect of the 2018 Martian global dust storm on the CO₂ density in the lower nightside thermosphere observed from MAVEN/IUVS Lyman‐alpha absorption

Abstract : The MAVEN/IUVS instrument measures Lyman‐α emissions from interplanetary and martian hydrogen at the limb and through the extended corona of Mars. In June 2018, a Global Dust Storm (GDS) surrounded Mars for a few months, heating the lower atmosphere and leading to an expansion of the Martian atmosphere. Nightside IUVS observations before and throughout this GDS showed the altitude of CO2 absorption of Lyman‐α photons in the thermosphere to increase by 4.5±1.0 km on 8 June 2018. This shift is attributed to an increase of the CO2 density by a factor 1.9±0.2 at 110 km due to the heating of the lower atmosphere. These nightside observations, not previously used to study dust storms, in an altitude range not sampled by other instruments, are consistent with dayside MAVEN observations and allow for more comprehensive determination of the global changes produced by the GDS on the Martian thermosphere.