Mars Hot Oxygen Density and Effective Temperature Derived From the MAVEN IUVS Observations

Abstract

The escape of hot oxygen atoms from Mars is important for the evolution of the planet's H2O and CO2 inventories. Owing to the lack of data constraints prior to the Mars Atmosphere and Volatile Evolution (MAVEN) mission, previous understanding of this key loss channel of the Mars atmosphere relied mostly on physics‐based models. Using the optical observations from the MAVEN Imaging Ultraviolet Spectrograph (IUVS) during 2014–2018, we perform the first inversion analysis of the coronal scans at 130.4 nm to quantify the density and effective temperature of the Mars hot oxygen corona. Our results indicate that the exobase densities of the hot oxygen atoms are ∼6.3–8.0 × 103 and ∼1.2 × 104 cm−3 during low and moderate solar activities, respectively, which agree well with recent empirical estimates using MAVEN's in situ measurements and, however, are about a factor of two higher than previous model predictions. The effective temperature varies only slightly between ∼4100–4500 K. The temperature and density variations with solar, seasonal, and dust conditions are consistent with previous models. Comparison with inversion results from IUVS limb scans indicates that the cold and the hot oxygen populations dominate below ∼200 and above ∼600 km, respectively, between which the kinetic distribution depends on both populations. Our results demonstrate for the first time the feasibility of extracting information about the Mars hot oxygen corona directly from optical observations, opening up a powerful means for monitoring the Mars oxygen escape on a global scale in future missions.

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

“…Escape flux of hot oxygen during different seasons can be calculated using these EMUS derived input parameters as well as the near-simultaneous in-situ neutral, ion and electron measurements from MAVEN (Chirakkil et al, 2022;Cravens et al, 2017;Lillis et al, 2017). The observed brightness is also a constraint on models of hot oxygen that can calculate not only the escape rate but also the hot oxygen density and effective temperature (Leblanc et al, 2017;Qin et al, 2024).…”

A Comparative Analysis of the Solar Ultraviolet Spectral Irradiance Measured from Earth and Mars: Toward a General Empirical Model for the Study of Planetary Aeronomy

“…Solar VUV radiation can be separated into X-ray ultraviolet (XUV, 0.1-10 nm), extreme ultraviolet (EUV, 10-120 nm), and farultraviolet (FUV, 120-200 nm) radiation, which can vary drastically by 1 or more orders of magnitude on timescales of minutes (e.g., due to eruptive solar flares), days (e.g., due to solar rotation with periods of ∼27 days), and years (e.g., due to solar cycle variations with periods of ∼11 yr), as well as on geometric scales (e.g., due to the varying distances of the Sun to Earth, Mars, and other planets) (Woods & Eparvier 2006;Woods 2008). Accurate estimation of solar VUV irradiance at various locations and times in the solar system is of critical importance for the study of planetary aeronomy, such as for the study of thermospheric and ionospheric variations (Haider et al 2002;Liu et al 2011;Zhang et al 2015), for the development of global circulation models (Solomon & Qian 2005;Qian et al 2008;Deng et al 2012), for the modeling of airglow emissions (Meier et al 2015;Solomon 2017;Qin 2020Qin , 2021Wan et al 2022;Qin et al 2023;Yin et al 2023;Qin et al 2024), for the prediction of space weather effects (Lathuillere et al 2002;Lilensten et al 2008), and for the study of climate evolution (Lilensten et al 2008;Persson et al 2020).…”