Chirakkil, Krishnaprasad, Deighan, Justin, Chaffin, Michael S., Jain, Sonal K., Lillis, Robert J., Raghuram, Susarla, Holsclaw, Greg, Brain, David A., Thiemann, Ed, Chamberlin, Phil, Fillingim, Matthew O., Evans, J. Scott, England, Scott, AlMatroushi, Hessa, AlMazmi, Hoor, Eparvier, Frank, Gacesa, Marko, El‐Kork, Nayla, and Curry, Shannon M.
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–day). 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. Plain Language Summary: The highly sensitive Emirates Mars Ultraviolet Spectrometer (EMUS) onboard Emirates Mars Mission (EMM) is capable of observing ultraviolet emissions emanating from Mars. Oxygen in the Martian exosphere is hard to see because it's tenuous. In this study, the analysis of long exposure time EMUS optical observations show that the hot oxygen corona on Mars has a short term variability due to solar rotation. Hot oxygen corona also shows a long–term variability that depends on the Sun–Mars distance and the solar cycle progression. When comparing data from two Martian years, it is noticed that the oxygen corona became brighter when the Sun is more active. Key Points: Brighter O corona is observed during perihelion and dimmer during aphelion, indicating a strong relationship with the Sun‐Mars distanceThe variation in OI 130.4 nm brightness shows a linear correlation with solar EUV irradiance, with a short‐term solar rotation periodicityInterannual variability is observed from MY 36 to MY 37, showing an enhancement in O corona brightness with the rise of Solar Cycle 25 [ABSTRACT FROM AUTHOR]