Discrete Aurora on Mars: Spectral Properties, Vertical Profiles, and Electron Energies

We present an analysis of hundreds of middle ultraviolet auroral spectra collected at the limb with the Imaging UltraViolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. While the companion paper by Schneider et al. (2021), https://doi.org/10.1029/2021JA029428 focuses on the detection, location, and occurrence frequency of discrete auroral events, this study addresses the spectral properties and vertical profiles of the auroral emissions. Our independent selection of events is based on a combination of automatic and manual detection methods with adequate signal‐to‐noise ratio of both the CO Cameron bands and the CO2+ ultraviolet doublet (UVD) at 190–270 and 288–289 nm, respectively. We find that the ratio of these two features remains quasi‐constant for UVD intensities exceeding ∼200 rayleighs (R), but the CO Cameron/CO2+ UVD ratio may become increasingly large for low UVD intensities. Three weak N2 Vegard‐Kaplan bands are identified in the Martian aurora for the first time. Limb profiles of the [OI] line at 297.2 nm indicate that the visible oxygen green line brightness may reach a few kilorayleighs. The distribution of the altitude of the emission peaks in the aurora is identical in and out of the region of crustal magnetic field located in the southern hemisphere. Comparisons of in situ measurements of electron energy spectra and ultraviolet auroral detections have been made for five optical detections. They generally show temporal coincidence but not necessarily quantitative agreement with the altitude and brightness expected from the characteristics of the measured electron energy spectra.

[1]  J. Gérard,et al.  Discrete Aurora on Mars: Insights Into Their Distribution and Activity From MAVEN/IUVS Observations , 2021, Journal of Geophysical Research: Space Physics.

[2]  F. Forget,et al.  On the derivation of thermospheric temperatures from dayglow emissions on Mars , 2021 .

[3]  J. Gérard,et al.  Laboratory Study of the Cameron Bands, the First Negative Bands, and Fourth Positive Bands in the Middle Ultraviolet 180–280 nm by Electron Impact Upon CO , 2020, Journal of Geophysical Research: Planets.

[4]  F. Lefévre,et al.  Imaging of Martian Circulation Patterns and Atmospheric Tides Through MAVEN/IUVS Nightglow Observations , 2020, Journal of Geophysical Research: Space Physics.

[5]  F. Daerden,et al.  Detection of green line emission in the dayside atmosphere of Mars from NOMAD-TGO observations , 2020, Nature Astronomy.

[6]  D. Mitchell,et al.  Inverted‐V Electron Acceleration Events Concurring With Localized Auroral Observations at Mars by MAVEN , 2020, Geophysical Research Letters.

[7]  J. Gérard,et al.  MAVEN‐IUVS Observations of the CO2+ UV Doublet and CO Cameron Bands in the Martian Thermosphere: Aeronomy, Seasonal, and Latitudinal Distribution , 2019, Journal of Geophysical Research: Space Physics.

[8]  F. Lefévre,et al.  Global Aurora on Mars During the September 2017 Space Weather Event , 2018, Geophysical Research Letters.

[9]  F. Montmessin,et al.  Observations of the Proton Aurora on Mars With SPICAM on Board Mars Express , 2017 .

[10]  J. Gérard,et al.  The Mars diffuse aurora: A model of ultraviolet and visible emissions , 2017 .

[11]  F. Lefévre,et al.  Nitric oxide nightglow and Martian mesospheric circulation from MAVEN/IUVS observations and LMD‐MGCM predictions , 2017 .

[12]  J. Gérard,et al.  Influence of the crustal magnetic field on the Mars aurora electron flux and UV brightness , 2017 .

[13]  B. Jakosky,et al.  Discovery of a proton aurora at Mars , 2016, Nature Astronomy.

[14]  J. Rouzaud,et al.  The MAVEN Solar Wind Electron Analyzer , 2016 .

[15]  J. Gérard,et al.  SPICAM observations and modeling of Mars aurorae , 2016 .

[16]  F. Montmessin,et al.  The Imaging Ultraviolet Spectrograph (IUVS) for the MAVEN Mission , 2015 .

[17]  F. Lefévre,et al.  New observations of molecular nitrogen in the Martian upper atmosphere by IUVS on MAVEN , 2015 .

[18]  B. Jakosky,et al.  Discovery of diffuse aurora on Mars , 2015, Science.

[19]  Mathieu Barthelemy,et al.  Prediction of blue, red and green aurorae at Mars , 2015 .

[20]  Aikaterini Radioti,et al.  Concurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express , 2015 .

[21]  R. Lillis,et al.  Electron impact ionization in the Martian atmosphere: Interplay between scattering and crustal magnetic field effects , 2015 .

[22]  A. Ridley,et al.  Mars Global Ionosphere‐Thermosphere Model: Solar cycle, seasonal, and diurnal variations of the Mars upper atmosphere , 2015 .

[23]  A. Bhardwaj,et al.  Model calculation of N2 Vegard‐Kaplan band emissions in Martian dayglow , 2011, 1108.0490.

[24]  J. Gérard,et al.  Mars ultraviolet dayglow variability: SPICAM observations and comparison with airglow model , 2010 .

[25]  R. Lundin,et al.  Observations of aurorae by SPICAM ultraviolet spectrograph on board Mars Express: Simultaneous ASPERA‐3 and MARSIS measurements , 2008 .

[26]  J. Gérard,et al.  Monte Carlo model of electron transport for the calculation of Mars dayglow emissions , 2008 .

[27]  D. Mitchell,et al.  Electron pitch angle distributions as indicators of magnetic field topology near Mars , 2007 .

[28]  F. Leblanc,et al.  SPICAM on Mars Express: Observing modes and overview of UV spectrometer data and scientific results , 2006 .

[29]  F. Leblanc,et al.  Martian dayglow as seen by the SPICAM UV spectrograph on Mars Express , 2006 .

[30]  D. Mitchell,et al.  On the origin of aurorae on Mars , 2006 .

[31]  Oleg Korablev,et al.  Discovery of an aurora on Mars , 2005, Nature.

[32]  Tatsuo Tabata,et al.  ANALYTIC CROSS SECTIONS FOR ELECTRON COLLISIONS WITH CO, CO2, AND H2O RELEVANT TO EDGE PLASMA IMPURITIES , 2001 .

[33]  S. Avakyan,et al.  Collision Processes and Excitation of UV Emission from Planetary Atmospheric Gases , 1999 .

[34]  J. Gérard,et al.  A kinetic model of the formation of the hot oxygen geocorona. 1: Quiet geomagnetic conditions , 1994 .

[35]  E. C. Zipf,et al.  Electron-impact excitation of the Cameron system (a3π → X1Σ)of CO , 1983 .

[36]  J. Ajello Emission Cross Sections of CO by Electron Impact in the Interval 1260–5000 Å. I , 1971 .

[37]  J. Gérard,et al.  Mars thermospheric scale height: CO Cameron and CO2+ dayglow observations from Mars Express , 2015 .

[38]  P. Bogdanovich,et al.  Atomic Data and Nuclear Data Tables , 2013 .