Retrieval of Ar, N2, O, and CO in the Martian thermosphere using dayglow limb observations by EMM EMUS

The Emirates Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars
Mission (EMM) Hope probe images Mars at wavelengths extending from
approximately 100 to 170 nm. EMUS observations began in February 2021 and
cover over a full Mars year. We report the first limb scan observations at
Mars of ultraviolet emissions Ar I 106.6 nm, N I 120 nm, and carbon
monoxide (CO) Fourth Positive Group (A - X) band system excited by
electron impact on CO. We use EMUS limb scan observations to retrieve
number density profiles of argon, molecular nitrogen, atomic oxygen, and
CO in the upper atmosphere of Mars from 130 to 160 km. CO is a sensitive
tracer of the thermal profile and winds in Mars' middle atmosphere
and the chemistry that balances CO2 in the atmosphere of Mars. EMUS
insertion orbit special observations demonstrate that far ultraviolet limb
measurements of the Martian thermosphere can be spectroscopically analyzed
with a robust retrieval algorithm to further quantify variations of CO
composition in the Martian upper atmosphere.