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.

Past and present remote sensing observations and in situ measurements of the Martian atmosphere, augmented by robust multidimensional modeling efforts, have demonstrated that loss of atomic oxygen and hydrogen into space has irreversibly depleted Mars' atmospheric water reservoir (Chaffin et al., 2017;Stone et al., 2020). The drivers of thermal escape of hydrogen are primarily space weather, waves and tides, and lower atmosphere dynamics related to dust storms and deep convection. Understanding the loss of water at Mars therefore requires that we establish a direct causal link between Mars' water reservoir, lower atmosphere weather, and vertical transport mechanisms. Quantifying the coupling between the lower, middle, and upper atmospheres of Mars, especially during solar

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Proton aurora at Mars were discovered using Mars Atmosphere and Volatile EvolutioN (MAVEN) mission Imaging UltraViolet Spectrograph (IUVS) limb scan observations (Deighan et al., 2018). The aurora results from the collision of H Energetic Neutral Atoms (ENAs) and protons with the bulk atmosphere, with every collision potentially resulting in an electronically excited ENA that promptly emits H spectrum photons. These H ENAs are produced upstream of the Martian bow shock when solar wind protons charge exchange with Mars coronal H, resulting in neutrals with the solar wind velocity that are not deflected around the bow shock with the rest of the solar wind (Ramstad et al., 2022). Ritter et al. (2018) showed that proton aurora can be triggered by coronal mass ejections and/or corotating interaction regions, consistent with this formation mechanism. In addition to proton aurora, this process results in thermospheric penetrating protons (Halekas et al., 2015) and H − ions (Jones et al., 2022), as well as coronal H pickup ions (Rahmati et al., 2018) and proton cyclotron waves (Romeo Abstract Proton aurora at Mars are thought to form indirectly, as a result of solar wind proton charge exchange with planetary coronal hydrogen upstream of the bow shock. This charge exchange produces beamed energetic neutral atoms that bypass the induced magnetosphere and cause spatially uniform auroral emission when they collide with the thermosphere. Here we report multiple definitive observations of spatially localized "patchy" proton aurora at Mars using the Emirates Mars Ultraviolet Spectrometer on the Emirates Mars Mission, and characterize the plasma environment during these events using contemporaneous Mars Atmosphere and Volatile EvolutioN mission measurements. Multiple mechanisms are required to explain these observations, including at times the direct deposition of solar wind plasma into the thermosphere, particularly during radial interplanetary magnetic field conditions. Much future work will be needed to assess these mechanisms and understand the impact of these auroral events on Mars atmospheric evolution.Plain Language Summary Even though Mars does not have a global magnetic field like the Earth, it still possesses multiple kinds of aurora. One of these is proton aurora, which is thought to form mainly by an indirect process that allows a small fraction of the solar wind to rain down on the planet uniformly across the dayside. We present observations of patchy proton aurora at Mars that require a different explanation. By examining multiple Emirates Mars Mission observations of patchy aurora that have different shapes and locations, and combining these images with plasma measurements made by NASA's Mars Atmosphere and Volatile EvolutioN mission, we conclude that a number of processes can produce patchy aurora. This patchy aurora is mostly the result of plasma turbulence, which under some circumstances leads to direct deposition of the solar wind across the entire Martian dayside, with a potentially large impact on long term ...