Airglow and Aurora in the Martian Atmosphere: Contributions by the Mars Express and ExoMars TGO Missions

Abstract

The study of atmospheric emissions from orbit to probe the middle and upper atmosphere of Mars, which started with the Mariner missions, is living a golden era thanks to the European Space Agency (ESA) Mars Express mission and other subsequent missions built upon its success, including the ESA ExoMars Trace Gas Orbiter (TGO) mission. Here we summarize the most relevant information obtained by the analysis of atmospheric emissions data from Mars Express and TGO, about the temperature and density structure, the atmospheric dynamics, the chemistry and the atmospheric escape to space. Mars Express also opened a new field of research on Mars with the discovery of aurorae on the planet. We present here the most outstanding results collected by Mars Express about aurorae. Finally, we also discuss how later measurements by other missions have complemented Mars Express and TGO results, and the potential future developments relevant to this field of research.

EMM EMUS Observations of FUV Aurora on Mars: Dependence on Magnetic Topology, Local Time, and Season

“…electron discrete aurora), first identified by the SPICAM (SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) ultraviolet spectrometer on Mars Express (Bertaux et al, 2005(Bertaux et al, , 2006Leblanc et al, 2006;Soret et al, 2016), are spatially confined photon emissions in Mars' nightside upper atmosphere, generated by the decay of electronic states in atoms and molecules primarily excited by suprathermal electrons (energies greater than ∼9 eV; Soret et al (2024)). These discrete aurorae (a total of 19 detections by SPICAM: 16 in nadir mode and 3 in limb mode), distinguishable by their small spatial scales and association with strong vertical crustal magnetic fields, differ significantly from other Mars auroral types (González-Galindo et al, 2024;Haider et al, 2022): diffuse aurora, caused by the global precipitation of solar energetic particles (Gérard et al, 2017;Nakamura et al, 2022;Schneider et al, 2015Schneider et al, , 2018, and proton aurora, resulting from solar wind protons directly entering the upper atmosphere after charge exchange with neutral hydrogen in the corona (Chaffin et al, 2022;Deighan et al, 2018;Gérard et al, 2019;Hughes et al, 2019;Ritter et al, 2018).…”