We present a comprehensive study of the nightside discrete electron aurora phenomenon on Mars, utilizing observations from EMUS onboard EMM. The oxygen emission at 130.4 nm is by far the brightest FUV auroral emission line observed at Mars. We identify auroral pixels in OI 130.4 nm disk observations, with higher sensitivity than previously possible. Our statistical analysis reveals regional, SZA, local time, and seasonal dependencies of auroral occurrence. Higher occurrence of aurora is observed in regions of open magnetic topology and vertical crustal magnetic fields. Aurora occurs more frequently closer to the terminator and is more likely on the dusk versus dawn sides of the night hemisphere. A pronounced auroral feature appears close to midnight local times in the southern hemisphere, consistent with the “spot” of energetic electron fluxes previously identified in the MGS data. The auroral spot is more frequent after midnight than before. Additionally, some regions on Mars are “aurora voids” where essentially no aurora occurs. The non-crustal field aurora exhibits a seasonal dependence, with major enhancements around Ls 235° (near perihelion) and Ls 30°. This is in line with the seasonal variability in ionospheric TEC observed by Mars Express, which is in turn related to the variability of solar irradiance and thermospheric density. Aurora occurrence also shows an increase with the rise of Solar Cycle 25. These observations not only shed light on where and when Martian aurora occurs, but also add to our understanding of Mars’ magnetic environment and its interaction with the heliospheric environment.

We present the first observations of the dayside coronal oxygen emission in far ultraviolet (FUV) measured by the Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM). The high sensitivity of EMUS is providing an opportunity to observe the tenuous oxygen corona in FUV, which is otherwise difficult to observe. Oxygen resonance fluorescence emission at 130.4 nm provides a measurement of the upper atmospheric and exospheric oxygen. More than 500 oxygen corona profiles are constructed using the long-exposure time cross-exospheric mode (OS4) of EMUS observations. These profiles range from ~200 km altitude up to several Mars radii (>6 RM) across all seasons and for two Mars years. Our analysis shows that OI 130.4 nm is highly correlated with solar irradiance (solar photoionizing and 130.4 nm illuminating irradiances) as well as changes in the Sun-Mars distance. The prominent short term periodicity in oxygen corona brightness is consistent with the solar rotation period (quasi-27-days). A comparison between the perihelion seasons of Mars Year (MY) 36 and MY 37 shows interannual variability with enhanced emission intensities during MY 37, due to the rise of Solar Cycle 25. These observations show a highly variable oxygen corona, which has significant implications on constraining the photochemical escape of atomic oxygen from Mars.

Mars’ ultraviolet airglow has been used to study its upper atmosphere for over four decades. Identifying variations in emission features has provided information on composition, density and temperature. The Emirates Mars Ultraviolet Spectrometer onboard the Emirates Mars Mission observes Mars’ airglow at Far and Extreme UV wavelengths. Variations in disk emission features are studied, with a focus on O I 1304 Å, CO Fourth Positive Group and C I 1561 Å. All show variations with local time and emission angle as expected. Dawn-dusk asymmetry observed is attributed to local time differences in advection. Variations in the brightness of several dayglow features, including 1304 Å, with irregular shapes are noted in around 25% of the disk images. These display some local time and hemispheric asymmetry in their occurrence rates. Examination of their spatial structure, occurrence, and spectra suggests these are associated with variations in composition and photoelectron flux.