Revealing a High Water Abundance in the Upper Mesosphere of Mars With ACS Onboard TGO

We present the first water vapor profiles encompassing upper mesosphere of Mars, 100–120 km, far exceeding maximum altitudes where remote sensing has been able to observe date. Our results are based on solar occultation measurements by Atmospheric Chemistry Suite (ACS) onboard ExoMars Trace Gas Orbiter (TGO). The observed wavelength range around 2.7 ?m possesses strong CO2 and H2O absorption lines allowing sensitive temperature density retrievals. report a mixing ratio varying from 10 50 ppmv at km during global dust storm (GDS) Martian Year (MY) 34 southern summer solstice MY 35. During other seasons remains persistently below ?2 ppmv. claim that contributions MY34 GDS perihelion periods into projected hydrogen escape Mars nearly equivalent.