Retrieval of CO Relative Column Abundance in the Martian Thermosphere From FUV Disk Observations by EMM EMUS

Abstract

Carbon monoxide (CO) is a sensitive tracer of the thermal profile and winds in Mars' middle atmosphere and the chemistry that balances CO2 in the whole atmosphere of Mars. The Emirates Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission Hope probe images Mars at ultraviolet wavelengths from approximately 100 to 170 nm. ΣCO/CO2, the column density ratio of CO to carbon dioxide, provides a sensitive measure of CO relative variability within the Martian thermosphere. Derived from the heritage of ΣO/N2 used at Earth, the ΣCO/CO2 algorithm uses emission from the CO Fourth Positive Group band system to derive the relative column abundance of CO above ∼70 km. We describe the EMUS ΣCO/CO2 algorithm, review the Level 3 data product, and discuss preliminary validation of the algorithm. The ΣCO/CO2 algorithm produces column density ratios that characterize the spatial structure and relative variability of CO abundance in the Martian thermosphere.

Morphology of Extreme and Far Ultraviolet Martian Airglow Emissions Observed by the EMUS Instrument on Board the Emirates Mars Mission

“…The use of the MLR technique is the best way to retrieve the brightnesses of the blended emissions if the correct model templates are known. Based on the recent lab data for electron impact on CO (Evans, Correira et al., 2022; Evans, Deighan et al., 2022; Lee et al., 2021), we are able to retrieve the brightness of various emissions that are blended by CO 4PG and that may explain the discrepancies between the few blended emissions between the HUT and our observations.…”

“…This may explain the increasing trend with the Mars season as it orbits around the sun. The OI 130.4 nm and Ar 106.6 nm emissions are also optically thick but have contribution from electron impact also (Evans, Correira et al., 2022; Evans, Deighan et al., 2022; Ritter et al., 2019), and both emissions show strong seasonal variation.…”

“…(2000) reported a total CO column density of 3.4 × 10 16 cm −2 using the atmosphere model from Fox and Dalgarno (1979). Using the opportunistic limb measurements from the EMM insertion orbit (the solar activity was similar to the HUT observation) and Mars Climate Data 5.3 model atmosphere (Forget et al., 1999; Millour et al., 2019) we calculate a mean value of 1.9 × 10 17 cm −2 for CO column (Evans, Correira et al., 2022; Evans, Deighan et al., 2022), that seems to be consistent with the values derived by Feldman et al. (2000).…”

“…We used Level 2b, version 2 data in this analysis which contains brightness for various EUV and FUV features that are used in this analysis. We use the Poisson multiple linear regression (MLR) technique that uses the model templates for each emission presented in the EMUS data to retrieve the best‐fit radiance for various EUV and FUV emissions (Evans, Correira et al., 2022; Evans, Deighan et al., 2022) that are provided in publicly available L2b data. This approach is similar to that used by Jain et al.…”

Emirates Mars Ultraviolet Spectrometer's (EMUS) Observation of Argon in the Martian Thermosphere

“…Understanding the distribution of Ar has been of interest to scientists for some time, as it is a good tracer of atmospheric circulation and can provide input on how to constrain transport parameters in Mars Global Climate Models (GCMs) (Sprague et al., 2012). Moreover, analyzing inert Ar with other ultraviolet emissions in the thermosphere, such as photochemically active carbon monoxide and atomic oxygen, can also provide insight on vertical transport (see Evans et al., 2022, this issue & England et al., 2022 this issue). Argon emission lines on Mars were first detected in 1995 by the Hopkins Ultraviolet Telescope (HUT) (Feldman et al., 2000), and since then measurements have also been made by the Far Ultraviolet Spectroscopic Explorer (FUSE) (Krasnopolsky & Feldman, 2002).…”