Characteristics of Mars UV Dayglow Emissions From Atomic Oxygen at 130.4 and 135.6 nm: MAVEN/IUVS Limb Observations and Modeling

Abstract

We present an overview of two Martian Years (MYs) oxygen dayglow limb observations of the ultraviolet (UV) emissions at 130.4 and 135.6 nm. The data have been collected with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We use solar flux measurements of EUVM on board MAVEN to remove the solar-induced variation and show the variations of the maximum limb brightness and altitude with season, solar zenith angle, and latitude, which reflects the strong variability of the Martian atmosphere. The 130.4-and 135.6-nm peak brightness and altitudes are strongly correlated and behave similarly. Both emissions are modeled for selected data using Monte Carlo codes to calculate emissions arising from electron impact on O and CO 2. Additional radiative transfer calculations are made to analyze the optically thick 130.4-nm emission. Model atmospheres from the Mars Climate Database serve as input. Both simulated limb profiles are in good agreement with the observations despite some deviations. We furthermore show that the observed 130.4-nm brightness is dominated by resonance scattering of the solar multiplet with a contribution (15-20%) by electron impact on O. Over 95% of the excitation at 135.6 nm arises from electron impact on O. Simulations indicate that the limb brightness is dependent on the oxygen and CO 2 content, while the peak emission altitude is mainly driven by the CO 2 content because of absorption processes. We deduce [O]/[CO 2 ] mixing ratios of 3.1% and 3.0% at 130 km for data sets collected at L S = 350°in Martian years 32 and 33.

Martian Oxygen and Hydrogen Upper Atmospheres Responding to Solar and Dust Storm Drivers: Hisaki Space Telescope Observations

“…Based on the ratio of observed and calculated boundary brightness shown in Table 3, the 130.4 nm emission is optically thick over our observation periods, which is consistent with past works (e.g., Chaufray et al., 2009; Ritter et al., 2019; Strickland & Donahue, 1970; Strickland et al., 1973). Thus, it is difficult to retrieve the absolute column density of oxygen atoms.…”

“…The former would directly increase O density in the upper atmosphere. The latter would increase photoelectrons in the ionosphere, which would affect the 130.4 nm brightness through increasing electron impact excitations of 130.4 nm (Ritter et al., 2019). It is possible that oxygen atoms are transported from the CSS, but Crismani et al.…”

“…The hydrogen and oxygen atoms have particularly strong resonant scattering emission lines in the EUV range at 121.6 nm (or Ly‐α) and 130.4 nm, respectively. Electron impact on oxygen atoms also contribute the 130.4 nm emission (Ritter et al., 2019). On Mars, these airglow emissions were observed by Mariner 6 and 7 spacecraft (Anderson & Hord, 1971; Barth et al., 1971; Strickland et al., 1972), followed by multiple spacecraft such as Mariner 9 (Anderson, 1974; Strickland et al., 1973), Mars Express (Chaufray et al., 2008; Chaufray et al., ; Leblanc, Chaufray, Lilensten, Witasse, & Bertaux, 2006), and Mars Atmosphere and Volatile Evolution (MAVEN) (Chaffin et al., 2015, 2018; Chaufray et al., 2015; Deighan et al., 2015; Ritter et al., 2019).…”

“…Recent observations showed that the limb peak brightness of oxygen 130.4 nm is highly correlated with the solar EUV flux (Ritter et al., 2019), while there is an additional factor that controls the brightness of Ly‐α airglow (Chaffin et al., 2014; Clarke et al., 2014). A most likely scenario is that the abundance of hydrogen atoms in the upper atmosphere is controlled by lower atmospheric dynamics such as dust storms that affect the atmospheric temperature and circulation.…”

“…Electron impact on oxygen atoms also contribute the 130.4 nm emission (Ritter et al., 2019). On Mars, these airglow emissions were observed by Mariner 6 and 7 spacecraft (Anderson & Hord, 1971; Barth et al., 1971; Strickland et al., 1972), followed by multiple spacecraft such as Mariner 9 (Anderson, 1974; Strickland et al., 1973), Mars Express (Chaufray et al., 2008; Chaufray et al., ; Leblanc, Chaufray, Lilensten, Witasse, & Bertaux, 2006), and Mars Atmosphere and Volatile Evolution (MAVEN) (Chaffin et al., 2015, 2018; Chaufray et al., 2015; Deighan et al., 2015; Ritter et al., 2019). The hydrogen and oxygen airglow emissions were also observed by Earth‐based missions by Hopkins Ultraviolet Telescope (HUT) on the space shuttle Endeavor (Feldman, Burgh, Durrance, & Davidsen, 2000) and Hubble Space Telescope (HST) (Bhattacharyya, Clarke, Bertaux, Chaufray, & Mayyasi, 2015; Clarke et al., 2014).…”