Thermal Structure of the Middle and Upper Atmosphere of Mars from
ACS/TGO CO2 Spectroscopy
Abstract
Temperature and density in the upper Martian atmosphere, above
~100 km, are key diagnostic parameters to study
processes of the species’ escape, investigate the impact of solar
activity, model the atmospheric circulation, and plan spacecraft descent
or aerobraking maneuvers. In this paper, we report vertical profiling of
carbon dioxide (CO2) density and temperature from the Atmospheric
Chemistry Suite (ACS) solar occultations onboard the ExoMars Trace Gas
Orbiter (TGO). A strong CO2 absorption band near 2.7 μm observed by the
middle infrared spectrometric channel (ACS MIR) allows the retrieval of
the atmospheric thermal structure in a large altitude range, from 20 to
180 km. We present the latitudinal and seasonal climatology of the
thermal structure for 1.5 Martian years (MYs), from the middle of MY 34
to the end of MY 35. The results show the variability of distinct
atmospheric layers, such as a mesopause (derived from 70 to 150 km) and
homopause, changing from 80-90 km at aphelion to 100-110 km at
perihelion. Some short-term homopause fluctuations are also observed
depending on the dust activity.