Soret, Lauriane ; Gérard, Jean-Claude ; Ritter, Birgit ; Schneider, Nick M. ; Jain, Sonal K. ; Milby, Zachary

Poster presented at AGU Fall Meeting 2020 on 2020-12-11

Abstract: Three types of aurorae have been observed in the Martian atmosphere: the discrete, the diffuse (Schneider, 2015) and the proton aurora (Deighan et al., 2018, Ritter et al., 2018). This work concentrates on discrete aurorae, which were first discovered with the ESA Mars Express SPICAM instrument (Bertaux et al., 2005). Discrete aurorae are very localized in space, time and altitude (Leblanc et al., 2008, Gérard et al., 2015, Soret et al., 2016). They are generated by the precipitation of energetic electrons. They are characterized by the presence of the CO (a3Π–X1Σ) Cameron bands between 190 and 270 nm, the CO (A1Π–X1Σ+) Fourth Positive system (CO 4P) between 135 and 170 nm, the (B2Σu+–X2Πg) doublet at 289 nm, the OI at 297.2 nm and the 130.4 nm OI triplet emissions (see figure 1). Figure 1: Spectral signature of a discrete auroral event observed with MAVEN IUVS. The discrete aurora can now be studied using observations from the MAVEN-IUVS ultraviolet spectrograph (Schneider et al., 2019). More than 10,000 orbits of the IUVS instrument acquired from 2014 to 2020 have been analyzed for this study. Auroral signatures were automatically selected in 69 different orbits. The spectral emissions intensities have been quantified and the auroral event altitudes of the tangent point have been estimated using limb profiles. We confirm that the CO Cameron bands emission layer is located between 105 and 165 km (Bertaux et al., 2005, Soret et al., 2016). We also show that the CO Cameron bands intensity varies linearly with the CO2+ UVD intensity. Finally, we use the MAVEN Solar Wind Electron Analyzer (SWEA) measurements and a Monte-Carlo model to estimate the electron energy needed to produce a discrete auroral event. These results are of a great importance to understand the production mechanisms of discrete aurorae on Mars. References: Bertaux J.-L. et al., 2005, Discovery of an aurora on Mars, Nature 435, 790–794, https://doi.org/10.1038/nature03603 Deighan J. et al., 2018, Discovery of a proton aurora at Mars, Nature Astronomy, vol. 2, 802-807, https://doi.org/10.1038/s41550-018-0538-5 Gérard J.-C. et al., 2015, Concurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express, J. Geophys. Res. Space Physics, 120,6749–6765, https://doi.org/10.1002/2015JA021150 Leblanc F. et al., 2008, Observations of aurorae by SPICAM ultraviolet spectrograph on board Mars Express: Simultaneous ASPERA-3 and MARSIS measurements, J. Geophys. Res., 113, A08311, http://dx.doi.org/10.1029/2008JA013033 Ritter B. et al., 2018, Observations of the proton aurora on Mars with SPICAM on board Mars Express, Geophysical Research Letters, 45, 612–619, https://doi.org/10.1002/2017GL076235 Schneider N. et al., 2015, Discovery of diffuse aurora on Mars, Science, 350, 1-5, https://doi.org/10.1126/science.aad0313 Schneider N. et al., 2019, MAVEN Remote Sensing and In Situ Observations of Discrete Aurora on Mars, AGU Fall meeting, SM42B-03, https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/506680 Soret L. et al., SPICAM observations and modeling of Mars aurorae, 2016, Icarus, 264, 398-406, https://doi.org/10.1016/j.icarus.2015.09.023