EMM EMUS Observations of Hot Oxygen Corona at Mars: Radial Distribution and Temporal Variability

Abstract

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.

Variability of Atomic Hydrogen Brightness in the Martian Exosphere: Insights From the Emirates Ultraviolet Spectrometer on Board Emirates Mars Mission

“…In addition to the atomic hydrogen Lyman emissions, variations in the atomic oxygen emission feature at 130.4 nm are discernible in this figure. Further exploration of the spatial and temporal variability of atomic emissions in these oxygen observations is discussed in a separate study (Chirakkil et al, 2024). The emission feature near 133.5 nm is due to singly ionized carbon atom, which has importance in studying the elemental abundance of dust components in the Interstellar medium (Slavin, 2009).…”

“…Consequently, the observed seasonal variation in H Ly-β predominantly reflects the variability of hydrogen rather than the involvement of atomic oxygen. This is supported by the fact that above 500 km, the hot oxygen component, which is bound to Mars, is significantly smaller by several orders of magnitude and rapidly decreases with increasing altitude (Chaffin et al, 2021;Chirakkil et al, 2024;Deighan et al, 2015). However, the background observations of EMUS are done above 20,000 km tangential altitude, where the role of atomic oxygen can safely be neglected.…”