References of "Stiepen, Arnaud"
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See detailCirculation Patterns in the Martian Nightside Upper Atmosphere Revealed by Nitric Oxide Nightglow
Milby, Z.; Stiepen, Arnaud ULiege; Schneider, N. et al

Conference (2019, July 01)

We will present a summary of ultraviolet spectroscopic studies of an atmospheric nightglow phenomenon which traces dynamics between Mars's upper and middle atmospheres using MAVEN data.

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See detailMartian upper-atmosphere circulation and tides revealed through MAVEN/IUVS observations of nitric oxide nightglow.
Milby, Zachariah; Stiepen, Arnaud ULiege; Schneider, Nicholas et al

Conference (2019, July)

The nitric oxide δ and γ bands are ultraviolet emissions which reflect the production-rate of nitric oxide (NO) from the recombination of excited nitrogen and oxygen atoms. We use it as a tracer of the ... [more ▼]

The nitric oxide δ and γ bands are ultraviolet emissions which reflect the production-rate of nitric oxide (NO) from the recombination of excited nitrogen and oxygen atoms. We use it as a tracer of the dynamics between Mars's upper- and middle-atmospheres, particularly of day-to- night and summer-to-winter pole circulation. We analyse this rate as it varies over Mars's surface in mission-long aggregations and local-time divisions. Our data were gathered by the Mars Atmosphere and Volatile Evolution (MAVEN) mission's Imaging Ultraviolet Spectrograph (IUVS) and span different seasonal conditions and latitudes. The data span allows a limited comparison between two subsequent Mars years. In our previous study of atmospheric limb scans from a limited dataset (Stiepen 2017, doi:10.1002/2016JA023523), we discovered a wave-3 structure to the nightglow at equatorial latitudes. For this study, we use scans taken of the full disk of Mars as seen at apoapse over 1.25 Mars years. We observe the same wave-3 structure, but find seasonal and local-time dependencies on position and brightness. We also discovered a wave-2 structure in northern polar regions that persists through all observed local times and seasons. We compare this to a similar feature observed in polar ozone. We compare our observations to model calculations from the LMD-MGCM. We find the model generally under-predicts the brightness of the nightglow at all sub-polar latitudes, suggesting it over- estimates the efficiency of atomic transport to the poles. However, we also find that the model reproduces the observed equatorial wave-3 and polar wave-2 structures. We identify the dominant atmospheric tide component of the equatorial wave-3 structure and analysis of the local- time dependencies of the wave structures and the brightness across all latitudes. [less ▲]

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See detailMethane on Mars: New insights into the sensitivity of CH 4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration
Liuzzi, G.; Villanueva, G. L.; Mumma, M. J. et al

in Icarus (2019), 321

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and ... [more ▼]

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH 4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH 4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate. © 2018 Elsevier Inc. [less ▲]

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See detailMartian upper-atmosphere circulation and tides revealed through MAVEN/IUVS observations of nitric oxide nightglow
Schneider, N.M.; Stiepen, Arnaud ULiege; Milby, Z. et al

Conference (2018, December 11)

The nitric oxide δ and γ bands are ultraviolet emissions which reflect the production rate of nitric oxide (NO) from the recombination of excited nitrogen and oxygen atoms. We use it as a tracer of the ... [more ▼]

The nitric oxide δ and γ bands are ultraviolet emissions which reflect the production rate of nitric oxide (NO) from the recombination of excited nitrogen and oxygen atoms. We use it as a tracer of the dynamics between Mars’ upper- and middle-atmospheres, particularly of day-to-night and summer-to-winter pole circulation. We analyse this rate as it varies over Mars’ surface in mission-long aggregations and local-time divisions. Our data were gathered by the Mars Atmosphere and Volatile Evolution (MAVEN) mission’s Imaging UltraViolet Spectrograph (IUVS) and span different seasonal conditions and latitudes. The data span allows a limited comparison between two subsequent Mars years. In our previous study from a limited dataset of atmospheric limb scans (Stiepen 2017, doi:10.1002/2016JA023523), we discovered a wave-3 structure to the nightglow at equatorial latitudes. For this study, we use scans taken of the full disk of Mars as seen at apoapse over 1.25 Mars years. We observe the same wave-3 structure, and find strong seasonal and local-time dependencies on position and brightness. We also discovered a wave-2 structure in northern polar regions that persists through all observed local times and seasons. We compare our observations to model calculations from the LMD-MGCM. We find the model generally under-predicts the brightness of the nightglow at all sub-polar latitudes, suggesting it over-estimates the efficiency of atomic transport to the poles. However, we also find that the model reproduces the observed equatorial wave-3 and polar wave-2 structures. We identify the dominant atmospheric tide component of the equatorial wave-3 structure and analysis of the local-time dependencies of the wave structures and the brightness across all latitudes. We also compare the observed polar nightglow wave structure to contemporaneous dayside ozone distributions also measured by IUVS. [less ▲]

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See detailA chemical survey of exoplanets with ARIEL
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in Experimental Astronomy (2018)

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the ... [more ▼]

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet's birth, and evolution. ARIEL was conceived to observe a large number ( 1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H[SUB]2[/SUB]O, CO[SUB]2[/SUB], CH[SUB]4[/SUB] NH[SUB]3[/SUB], HCN, H[SUB]2[/SUB]S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed - using conservative estimates of mission performance and a full model of all significant noise sources in the measurement - using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL - in line with the stated mission objectives - will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives. [less ▲]

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See detailNOMAD, an Integrated Suite of Three Spectrometers for the ExoMars Trace Gas Mission: Technical Description, Science Objectives and Expected Performance
Vandaele, A. C.; Lopez-Moreno, J.-J.; Patel, M. R. et al

in Space Science Reviews (2018), 214

The NOMAD ("Nadir and Occultation for MArs Discovery") spectrometer suite on board the ExoMars Trace Gas Orbiter (TGO) has been designed to investigate the composition of Mars' atmosphere, with a ... [more ▼]

The NOMAD ("Nadir and Occultation for MArs Discovery") spectrometer suite on board the ExoMars Trace Gas Orbiter (TGO) has been designed to investigate the composition of Mars' atmosphere, with a particular focus on trace gases, clouds and dust. The detection sensitivity for trace gases is considerably improved compared to previous Mars missions, compliant with the science objectives of the TGO mission. This will allow for a major leap in our knowledge and understanding of the Martian atmospheric composition and the related physical and chemical processes. The instrument is a combination of three spectrometers, covering a spectral range from the UV to the mid-IR, and can perform solar occultation, nadir and limb observations. In this paper, we present the science objectives of the instrument and explain the technical principles of the three spectrometers. We also discuss the expected performance of the instrument in terms of spatial and temporal coverage and detection sensitivity. [less ▲]

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See detailDiscovery of a proton aurora at Mars
Deighan, J.; Jain, S. K.; Chaffin, M. S. et al

in Nature Astronomy (2018)

Proton aurorae are a distinct class of auroral phenomena caused by energetic protons precipitating into a planetary atmosphere. The defining observational signature is atomic hydrogen emissions from the ... [more ▼]

Proton aurorae are a distinct class of auroral phenomena caused by energetic protons precipitating into a planetary atmosphere. The defining observational signature is atomic hydrogen emissions from the precipitating particles after they obtain an electron from the neutral atmospheric gas, a process known as charge exchange. Until now, proton aurorae have been observed at Earth only. Here, we present evidence of auroral activity driven by precipitating protons at Mars, using observations by the MAVEN spacecraft. We observed transient brightening of upper atmospheric hydrogen Lyman-α emission across the Martian dayside correlated with solar wind activity. The driving mechanism is one not found at Earth and originates from energetic neutral atom production by solar wind protons directly interacting with the extended hydrogen corona surrounding Mars. We characterize this new type of Martian aurora and compare the observed emissions with preliminary modelling guided by simultaneous in situ particle measurements. These observations provide insights into how the solar wind can directly deposit energy into the Martian atmosphere as well as all other planetary objects that are surrounded by a substantial neutral corona exposed to the solar wind. [less ▲]

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See detailMars Nitric Oxide Nightglow and Its
Stiepen, Arnaud ULiege; MAVEN IUVS team; LMD-MGCM team

Conference (2018, July)

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See detailHighlights from Imaging Ultraviolet Spectroscopy of the Mars Atmosphere with MAVEN/IUVS
Stiepen, Arnaud ULiege; Chaffin; MAVEN IUVS team

Conference (2018, July)

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See detailGlobal aurora on Mars during the September 2017 Space Weather Event
Schneider; MAVEN IUVS team; Particle and Fields MAVEN team et al

Conference (2018, April)

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See detailMAVEN IUVS Remote Sensing Highlights Relevant to Upcoming TGO Observations
Chaffin, M.; Schneider, N. M.; Deighan, J. et al

in From Mars Express to ExoMars (2018, February 01)

Not Available

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See detail14 years of Mars' atmosphere monitoring by SPICAM on Mars Express
Lacombe, G.; Montmessin, F.; Korablev, O. et al

in From Mars Express to ExoMars (2018, February 01)

Not Available

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See detailMartian Thermospheric Response to an X8.2 Solar Flare on 10 September 2017 as Seen by MAVEN/IUVS
Jain, S. K.; Deighan, J.; Schneider, N. M. et al

in Geophysical Research Letters (2018), 45(15), 7312-7319

We report the response of the Martian upper atmosphere to a strong X-class flare on 10 September 2017 as observed by the Imaging Ultraviolet Spectrograph (IUVS) instrument aboard the Mars Atmosphere ... [more ▼]

We report the response of the Martian upper atmosphere to a strong X-class flare on 10 September 2017 as observed by the Imaging Ultraviolet Spectrograph (IUVS) instrument aboard the Mars Atmosphere Volatile EvolutioN (MAVEN) mission. The solar flare peaked at 16:24 hr UT, and IUVS dayglow observations were taken about an hour after the flare peak. Retrieved temperatures from IUVS dayglow observations show a significant increase during the flare orbit, with a mean value of ∼270 K and a maximum value of ∼310 K. The retrieved temperatures during the flare orbit also show a strong latitudinal gradient, indicating that the flare-induced heating is limited between low and middle latitudes. During this event IUVS observed an ∼70% increase in the observed brightness of CO+ 2 ultraviolet doublet and CO Cameron band emission at 90 km, where high-energy photons (< 10 nm) deposit most of their energy. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailGlobal Aurora on Mars During the September 2017 Space Weather Event
Schneider, N. M.; Jain, S. K.; Deighan, J. et al

in Geophysical Research Letters (2018), 45(15), 7391-7398

We report the detection of bright aurora spanning Mars' nightside during the space weather event occurring in September 2017. The phenomenon was similar to diffuse aurora detected previously at Mars, but ... [more ▼]

We report the detection of bright aurora spanning Mars' nightside during the space weather event occurring in September 2017. The phenomenon was similar to diffuse aurora detected previously at Mars, but 25 times brighter and detectable over the entire visible nightside. The observations were made with the Imaging UltraViolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile EvolutioN spacecraft orbiting Mars. Images show that the emission was brightest around the limb of the planet, with a fairly uniform faint glow against the disk itself. Spectra identified four molecular emissions associated with aurora, and limb scans show the emission originated from an altitude of ~60 km in the atmosphere. Both are consistent with very high energy particle precipitation. The auroral brightening peaked around 13 September, when the flux of solar energetic electrons and protons both peaked. During the declining phase of the event, faint but statistically significant auroral emissions briefly appeared against the disk of the planet in the form of narrow wisps and small patches. These features are approximately aligned with predicted open field lines in the region of strong crustal magnetic fields in Mars' southern hemisphere. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailMars H Escape Rates Derived From MAVEN/IUVS Lyman Alpha Brightness Measurements and Their Dependence on Model Assumptions
Chaffin, M. S.; Chaufray, J. Y.; Deighan, J. et al

in Journal of Geophysical Research. Planets (2018), 123(8), 2192-2210

Mars has lost a large fraction of its water to space, with the H component of this loss thought to occur mainly as a result of thermal (Jeans) escape from the upper atmosphere. Constraints on H loss have ... [more ▼]

Mars has lost a large fraction of its water to space, with the H component of this loss thought to occur mainly as a result of thermal (Jeans) escape from the upper atmosphere. Constraints on H loss have historically been made using hydrogen Lyman alpha (121.6 nm) light scattered in the planet's extended upper atmosphere or corona. Here we employ observations from the Mars Atmosphere and Volatile Evolution (MAVEN) mission's Imaging Ultraviolet Spectrograph (IUVS) to constrain H escape in December 2014 and August 2016, when MAVEN observed the dayside corona at low latitude. To obtain adequate fits and address systematic sources of uncertainty including instrument calibration, we fit in exobase number density and escape rate instead of density and temperature, employing Markov Chain Monte Carlo techniques. This produces better model fits to data than most previous analyses. When we assume a single population of H atoms, we obtain H temperatures inconsistent with expected trends and a shape mismatch between observed and modeled profiles, similar to previous studies. Introducing either a second population of H (at a distinct temperature and density) or adding deuterium to the corona allows for essentially perfect fits. Despite this model ambiguity, derived loss rates for both periods are within a factor of four, 3.3–8.8×108cm−2/s in December 2014 (Ls∼250) and 0.6–2.3×108cm−2/s in August 2016 (Ls∼200). These rates are similar to those found in prior studies and confirm the known seasonal trend—doing so while incorporating the substantial uncertainty in absolute calibration insufficiently explored by previous studies. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailSignificant Space Weather Impact on the Escape of Hydrogen From Mars
Mayyasi, M.; Bhattacharyya, D.; Clarke, J. et al

in Geophysical Research Letters (2018), 45(17), 8844-8852

In September 2017, an active region of the Sun produced a series of strong flares and a coronal mass ejection that swept past Mars producing enhanced ionization and heating in the upper atmosphere ... [more ▼]

In September 2017, an active region of the Sun produced a series of strong flares and a coronal mass ejection that swept past Mars producing enhanced ionization and heating in the upper atmosphere. Emissions from atmospheric hydrogen Lyman-α were also enhanced at Mars. Temperatures derived from neutral species scale heights were used in conjunction with the H Lyman-α observations to simulate the effects of this space weather event on Martian hydrogen properties in the exosphere. It was found that hydrogen abundance in the upper atmosphere decreased by ~25% and that the H escape rate increased by a factor of 5, mainly through an increase in upper atmospheric temperature. This significant escape rate variation is comparable to seasonally observed trends but occurred at much shorter timescales. Such solar events would statistically impact extrapolation of Martian water loss over time. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailUV Dayglow Variability on Mars: Simulation With a Global Climate Model and Comparison With SPICAM/MEx Data
González-Galindo, F.; Chaufray, J.-Y.; Forget, F. et al

in Journal of Geophysical Research. Planets (2018), 123(7), 1934-1952

A model able to simulate the CO Cameron bands and the CO + 2 UV doublet, two of the most prominent UV emissions in the Martian dayside, has been incorporated into a Mars global climate model. The model ... [more ▼]

A model able to simulate the CO Cameron bands and the CO + 2 UV doublet, two of the most prominent UV emissions in the Martian dayside, has been incorporated into a Mars global climate model. The model self-consistently quantifies the effects of atmospheric variability on the simulated dayglow for the first time. Comparison of the modeled peak intensities with Mars Express (MEx) SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) observations confirms previous suggestions that electron impact cross sections on CO2 and CO need to be reduced. The peak altitudes are well predicted by the model, except for the period of MY28 characterized by the presence of a global dust storm. Global maps of the simulated emission systems have been produced, showing a seasonal variability of the peak intensities dominated by the eccentricity of the Martian orbit. A significant contribution of the CO electron impact excitation to the Cameron bands is found, with variability linked to that of the CO abundance. This is in disagreement with previous theoretical models, due to the larger CO abundance predicted by our model. In addition, the contribution of this process increases with altitude, indicating that care should be taken when trying to derive temperatures from the scale height of this emission. The analysis of the geographical variability of the predicted intensities reflects the predicted density variability. In particular, a longitudinal variability dominated by a wave-3 pattern is obtained both in the predicted density and in the predicted peak altitudes. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailLoss of the Martian atmosphere to space: Present-day loss rates determined from MAVEN observations and integrated loss through time
Jakosky, B. M.; Brain, D.; Chaffin, M. et al

in Icarus (2018), 315

Observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a ... [more ▼]

Observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 – 3 Oct 2016). Loss rates for H and O are sufficient to remove ∼2–3 kg/s to space. By itself, this loss would be significant over the history of the planet. In addition, loss rates would have been greater early in history due to the enhanced solar EUV and more-active Sun. Integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar CO2 or 23 m global equivalent layer of H2O; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. Combined with the lack of surface or subsurface reservoirs for CO2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of Mars from an early, warmer environment to the cold, dry one that we see today. © 2018 Elsevier Inc. [less ▲]

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See detailThree types of aurora on Mars
Schneider, N.; Jain, S.; Deighan, J. et al

Conference (2017, December)

Observations by the Imaging UltraViolet Spectrograph (IUVS) on the MAVEN spacecraft have identified three types of aurora on Mars, each profoundly different from comparable types on Earth and other ... [more ▼]

Observations by the Imaging UltraViolet Spectrograph (IUVS) on the MAVEN spacecraft have identified three types of aurora on Mars, each profoundly different from comparable types on Earth and other planets. The primary reason for these differences is Mars’ lack of a global magnetic field and presence of localized crustral magnetic fields primarily in the southern hemisphere. IUVS is MAVEN’s remote sensing instrument for study of the Mars atmosphere. The instrument records spatially-resolved spectra in the far-UV (110-190 nm) and Mid-UV (180-340 nm). By virtue of an internal scan mirror and a gimbaled instrument platform, IUVS obtains useful spectra on Mars with >50% duty cycle, including Mars’ nightside. IUVS performs limb scans during the spacecraft periapse, and obtains UV images of the planet from reconstructed apoapse disk scans. Two types of aurora have been detected on Mars’ nightside by virtue of emissions requiring excitation by precipitating charged particles. The first type, discrete aurora, are localized near the boundary between open and closed crustal magnetic field lines. They generally appear at ~140 km altitude and the spectra correspond to moderate mean electron energy precipitation. These detections confirm the discovery of discrete discovered by Mars Express/SPICAM. IUVS has discovered a second type, diffuse aurora, which are widespread and potentially global. They occur as low as 70 km altitude; the spectra, depth of penetration and timing are consistent with the precipitation of relativistic electrons from the Sun. IUVS has discovered a third type, proton aurora, on Mars’ dayside as excess hydrogen Lyman alpha emission confined to Mars’ thermosphere. The intermittent excesses appear correlated with enhanced solar wind conditions. This type is the most common form of aurora detected by IUVS. IUVS results dispel a common misconception that aurora only occur near the edges of closed planetary magnetic field lines. While this is true for terrestrial aurora and discrete aurora on Mars, it is false for Mars’ diffuse and proton auroras. In this sense, Mars serves as the best archetype for auroral processes on unmagnetized planets in our solar system and beyond. [less ▲]

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See detailImproving MAVEN-IUVS Ly-Alpha apoapsis images
AlMannaei; Chaffin; Jain et al

Conference (2017, December)

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