Mars Discrete Aurora: A Comprehensive Survey for Detection & Characterization by MAVEN/IUVS

We present the results of a comprehensive search for discrete aurora emissions on Mars from six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a localized and transient form of aurora apparently unique to Mars, owing to its lack of a global magnetic Teld. The auroral emissions originate from precipitating electrons accelerated by the reconTguration of Mars' crustal magnetic Telds as the planet rotates relative to the external magnetic Teld carried by the solar wind. This process is distinct from other more widespread diffuse and proton aurora also seen at Mars. Discrete aurora was discovered in regions of strong crustal magnetic Telds by the SPICAM instrument on Mars Express using limb scanning [Bertaux et al., 2005]. The emission appeared in patches ~tens of km across at altitudes ~130 km. Further analysis revealed a total of 20 instances of auroral patches during 10 years of intermittent SPICAM observations [Gérard et al., 2015]. Auroral excitation was attributed to the precipitation of electrons, typically ~100 eV - 1 keV. MAVEN/IUVS obtained the Trst images of the phenomenon (Schneider et al. 2018). We have examined MAVEN's mission-long dataset of nightside limb scans spanning more than 10,000 orbits over nearly 6 Earth years. Events were identiTed by signiTcant emission in the CO Cameron bands (190-270 nm) and were individually conTrmed to be free of stray light and cosmic ray interference. More than 500 discrete aurora events were detected, increasing the number of known events by more than an order of magnitude. The Tgure shows a remarkable string of distinct events seen during a single 20-minute passage of Mars' crustal Teld region. The observed events show a strong concentration near crustal Telds in the south, but also exhibit a substantial distribution spread more uniformly over the entire planet. Some events are seen at the tangent altitude expected for electron precipitation, but many appear at lower projected altitudes. We infer these are small patches of emission in front of (or behind) the limb itself, and in some cases the spacecraft was probably imbedded in the emission. See also the related abstract by Soret et al., this conference

Characteristics of the Martian discrete auroral emissions observed with MAVEN-IUVS

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 less energetic electrons than for diffuse aurorae (hundreds of eV compared to tens of keV). Bertaux et al. (2005) showed that discrete aurorae 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 the ratio between the CO Cameron bands and the CO2+ UVD intensities. 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. See also the related abstract by Schneider et al., this conference, which looks in more detail at the occurrences and locations of the Martian discrete aurorae. 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.2015.09.02

A Search for Spectral Variations in Auroral Emissions from Mars

The Imaging Ultraviolet Spectrograph (IUVS) instrument onboard the MAVEN mission has been used to study several forms of aurora in the atmosphere of Mars; discrete aurora, discovered by the SPICAM instrument on Mars Express, as well as two other forms discovered by MAVEN/IUVS referred to as diffuse aurora and proton aurora. Each type of aurora can be identified through unique spectral characteristics. In particular, discrete aurora events are ultraviolet emissions spread variably throughout Mars’ upper atmosphere, and are strongly correlated to Mars’ crustal magnetic field. Discrete aurora events can be identified by strong emissions of CO Cameron bands, and slightly weaker emissions of CO2+ Ultraviolet Doublet. Based on recent work from our group, we expect to see a ratio of approximately 7 between these two emissions. However, several exceptions display spectral features that do not agree with characteristics of any of the currently known aurora types. These observations show the same two emissions as discrete aurora events. However, the ratio between the CO Cameron bands and CO2+ Ultraviolet Doublet is much higher than expected, ranging from a ratio of 10 to over 500. We have collected the observations containing these variations and will search for patterns and trends among them, such as proximity to the terminator, locations relative to crustal fields, or timing relative to space weather events. Using these trends, we will discuss possible explanations for the differences between this data and common discrete aurora observations

Seasonal and Diurnal Variation in Vertical Profiles of the Martian Nitric Oxide Nightglow Layer

The nitric oxide (NO) nightglow is a recombination reaction rate which traces flux between from the nightside Martian thermosphere to the mesosphere. Brighter emission occurs where descending air brings molecules deeper into the mesosphere, so we can use the reaction rate as a tracer of the dynamics between Mars’ thermosphere and mesosphere. We derive vertical profiles of NO nightglow brightness from limb-scan spectra observed by the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. This data set has broad seasonal, latitudinal, and local-time coverage, allowing us to comprehensively characterize the behavior of the nightglow layer by latitude, local time, and season and even analyze waves and tidal structures, greatly expanding the results of previous limb scan studies. We also compare these observations to simulations from the LMD-MGCM and corresponding insights into altitude- and temporal-dependence of temperature, downwelling wind velocity, and atomic N and O densities

Imaging of Martian Circulation Patterns and Atmospheric Tides Through MAVEN/IUVS Nightglow Observations

International audienceWe report results from a study of two consecutive Martian years of imaging observations of nitric oxide ultraviolet nightglow by the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution (MAVEN) mission spacecraft. The emission arises from recombination of N and O atoms in Mars' nightside mesosphere. The brightness traces the reaction rate as opposed to the abundance of constituents, revealing where circulation patterns concentrate N and O and enhance recombination. Emissions are brightest around the winter poles, with equatorial regions brightening around the equinoxes. These changes offer clear evidence of circulation patterns transitioning from a single cross-equatorial cell operating during solstice periods to more symmetric equator-to-poles circulation around the equinoxes. Prominent atmospheric tides intensify the emissions at different longitudes, latitude ranges and seasons. We find a strong eastward-propagating diurnal tide (DE2) near the equator during the equinoxes, with a remarkably bright spot narrowly confined near (0°, 0°). Wave features at the opposite winter poles are dissimilar, reflecting different circulation patterns at perihelion versus aphelion. LMD-MGCM simulations agree with the patterns of most observed phenomena, confirming that the model captures the dominant physical processes. At the south winter pole, however, the model fails to match a strong wave-1 spiral feature. Observed brightnesses exceed model predictions by a factor of 1.9 globally, probably an underestimation of the dayside production of N and O atoms. Further study of discrepancies between the model and observations offer opportunities to improve our understanding of chemical and transport processes controlling the emission

Competitive Exclusion of Intra-Genus <i>Salmonella</i> in Neonatal Broilers

Salmonellosis is a zoonotic infection caused by Salmonella enterica serotypes contracted from contaminated products. We hypothesized that competitive exclusion between Salmonella serotypes in neonatal broilers would reduce colonization and affect the host immune response. Day of hatch broilers were randomly allocated to one of six treatment groups: (1) control, which received saline, (2) Salmonella Kentucky (SK) only on day 1 (D1), (3) Salmonella Typhimurium (ST) or Salmonella Enteritidis (SE) only on D1, (4) SK on D1 then ST or SE on day 2 (D2), (5) ST or SE on D1 then SK on D2, and (6) SK and ST or SE concurrently on D1. Salmonella gut colonization and incidence were measured from cecal contents. Livers and spleens were combined and macerated to determine systemic translocation. Relative mRNA levels of interleukin-1β (IL-1β), IL-6, IL-10, IL-18, and gamma interferon (IFN-γ) were measured in cecal tonsils and liver to investigate local and systemic immune responses. When a serotype was administered first, it was able to significantly reduce colonization of the following serotype. Significant changes were found in mRNA expression of cytokines. These results suggest competitive exclusion by Salmonella enterica serotypes affect local and systemic immune responses

Imaging of Martian Circulation Patterns and Atmospheric Tides Through MAVEN/IUVS Nightglow Observations

International audienceWe report results from a study of two consecutive Martian years of imaging observations of nitric oxide ultraviolet nightglow by the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution (MAVEN) mission spacecraft. The emission arises from recombination of N and O atoms in Mars' nightside mesosphere. The brightness traces the reaction rate as opposed to the abundance of constituents, revealing where circulation patterns concentrate N and O and enhance recombination. Emissions are brightest around the winter poles, with equatorial regions brightening around the equinoxes. These changes offer clear evidence of circulation patterns transitioning from a single cross-equatorial cell operating during solstice periods to more symmetric equator-to-poles circulation around the equinoxes. Prominent atmospheric tides intensify the emissions at different longitudes, latitude ranges and seasons. We find a strong eastward-propagating diurnal tide (DE2) near the equator during the equinoxes, with a remarkably bright spot narrowly confined near (0°, 0°). Wave features at the opposite winter poles are dissimilar, reflecting different circulation patterns at perihelion versus aphelion. LMD-MGCM simulations agree with the patterns of most observed phenomena, confirming that the model captures the dominant physical processes. At the south winter pole, however, the model fails to match a strong wave-1 spiral feature. Observed brightnesses exceed model predictions by a factor of 1.9 globally, probably an underestimation of the dayside production of N and O atoms. Further study of discrepancies between the model and observations offer opportunities to improve our understanding of chemical and transport processes controlling the emission

Discrete Aurora at Mars: Dependence on Upstream Solar Wind Conditions

Discrete aurora at Mars, characterized by their small spatial scale and tendency to form near strong crustal magnetic fields, are emissions produced by particle precipitation into the Martian upper atmosphere. Since 2014, Mars Atmosphere and Volatile EvolutioN's (MAVEN's) Imaging Ultraviolet Spectrograph (IUVS) has obtained a large collection of UV discrete aurora observations during its routine periapsis nightside limb scans. Initial analysis of these observations has shown that, near the strongest crustal magnetic fields in the southern hemisphere, the IUVS discrete aurora detection frequency is highly sensitive to the interplanetary magnetic field (IMF) clock angle. However, the role of other solar wind properties in controlling the discrete aurora detection frequency has not yet been determined. In this work, we use the IUVS discrete aurora observations, along with MAVEN observations of the upstream solar wind, to determine how the discrete aurora detection frequency varies with solar wind dynamic pressure, IMF strength, and IMF cone angle. We find that, outside of the strong crustal field region (SCFR) in the southern hemisphere, the aurora detection frequency is relatively insensitive to the IMF orientation, but significantly increases with solar wind dynamic pressure, and moderately increases with IMF strength. Interestingly however, although high solar wind dynamic pressures cause more aurora to form, they have little impact on the brightness of the auroral emissions. Alternatively, inside the SCFR, the detection frequency is only moderately dependent on the solar wind dynamic pressure, and is much more sensitive to the IMF clock and cone angles. In the SCFR, aurora are unlikely to occur when the IMF points near the radial or anti-radial directions when the cone angle (arccos(B x /|B|)) is less than 30° or between 120° and 150°. Together, these results provide the first comprehensive characterization of how upstream solar wind conditions affect the formation of discrete aurora at Mars