Publications of Jean-Claude Gérard
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See detailObservations of satellite footprints in Jupiter's Aurorae
Mura, A.; Adriani, A.; Altieri, F. et al

Conference (2018, December 12)

JIRAM (Jovian Infrared Auroral Mapper) on board Juno is an imager/spectrometer in the 2-5 um range. One imaging channel is designed to study the Jovian H3+ auroral emissions. Its high angular resolution ... [more ▼]

JIRAM (Jovian Infrared Auroral Mapper) on board Juno is an imager/spectrometer in the 2-5 um range. One imaging channel is designed to study the Jovian H3+ auroral emissions. Its high angular resolution, combined with the unique vantage point provided by Juno, allows JIRAM to observe the aurorae in unprecedented detail. Here we present the results from ~2 years of observations of the auroral footprints of the Galilean moons. These are bright spots and associated tail that appear in Jupiter’s ionosphere at the base of the magnetic field lines which sweep past Io, Europa, and Ganymede. The moons are obstacles in the path of Jupiter’s rapidly rotating magnetospheric plasma, and the resulting electromagnetic interaction launches Alfvén waves along the magnetic field towards Jupiter, where intense electron bombardment of the hydrogen atmosphere causes it to glow. Recent observations reveal for the first time that the footprint of Io is comprised of a regularly spaced array of emission features, extending downstream of the leading footprint. Contrary to the larger spots seen in lower resolution images, the small scale of these multiple features (~100 km) is incompatible with the simple paradigm of multiple Alfvén wave reflections. Additionally, observations of Io’s trailing tail well downstream of the main footprint reveal a pair of closely spaced parallel arcs, previously unresolved. The temperatures of the main spot and tail, retrieved with the JIRAM spectrometer, are lower than the main auroral oval. This could indicate that the emission is located at a deeper level, possibly caused by higher energy electrons. Ganymede’s footprint spots (main and secondary) appear as a pair of emission features that provide a remote measure of the size Ganymede’s magnetosphere, mapped from its distant orbit onto Jupiter’s magnetosphere. [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, A.; 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 detailObservations of Jupiter by the Juno Ultraviolet Spectrograph (Juno-UVS)
Greathouse, T. E.; Gladstone, G.R.; Hue, V. et al

Conference (2018, September 20)

We present an overview of the science performed by Juno’s Ultraviolet Spectrograph, UVS, over the first 11 successful perijove sequences performed since orbital insertion on July 4th, 2016. We will ... [more ▼]

We present an overview of the science performed by Juno’s Ultraviolet Spectrograph, UVS, over the first 11 successful perijove sequences performed since orbital insertion on July 4th, 2016. We will discuss the measured local time dependence of Jupiter’s polar auroral emissions, simultaneous UV and H3+ observations and their correlations or lack thereof, evolution and morphology of Io’s magnetic footprint in Jupiter’s atmosphere, measurements concerning the spatial and temporal variation of high energy particles (>7 MeV) in the polar regions of Jupiter’s magnetosphere, and finally the production of a dataset that could be used to produce an all sky UV stellar atlas at wavelengths between 70 and 205 nm. [less ▲]

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See detailCO2 variations in the Martian lower thermosphere from IUVS-MAVEN airglow observations.
Gkouvelis, Leonardos; Gérard, Jean-Claude ULiege; Ritter, Birgit ULiege et al

Conference (2018, September 17)

IUVS-MAVEN limb observations have been performed since 2014. We have analyzed almost four years of observations focusing on the O(1S) 297.2 nm dayglow emission line. We have developed an automatic ... [more ▼]

IUVS-MAVEN limb observations have been performed since 2014. We have analyzed almost four years of observations focusing on the O(1S) 297.2 nm dayglow emission line. We have developed an automatic methodology to retrieve the CO2 column densities near 80 km, a region difficult to probe by other techniques. We present nearly two Martian years of observations of pressure variations at different latitudes and comparisons withMCD model predictions. Generally, the best agreement is reached following scaling down of the MCD values from 0.3 to 0.8 to fit the observations. This result was previously expected on the basis of model comparisons with ultraviolet occultation measurements. [less ▲]

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See detailMars emissions from CO and CO2+: IUVS-MAVEN limb observations and model
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Ritter, Birgit ULiege et al

Poster (2018, September 17)

The IUVS Ultraviolet spectrograph (McClintock et al. 2014) on board MAVEN has been collecting thousands of airglow (Jain et al. 2015) or auroral (Schneider et al., 2015) limb profiles in the range 120 to ... [more ▼]

The IUVS Ultraviolet spectrograph (McClintock et al. 2014) on board MAVEN has been collecting thousands of airglow (Jain et al. 2015) or auroral (Schneider et al., 2015) limb profiles in the range 120 to 340 nm (Fig. 1) since November 2014. We have analyzed more that three years of airglow observations and compared them to model simulations. MAVEN has been quasi-continuously collecting airglow observations since November 2014, covering more than 1.5 Martian year and various latitudes ranges. The main features are emissions from CO, CO2+, O, N2 and C. In this work, we compare the characteristics of the CO2+ ultraviolet doublet (UVD) limb profiles with model simulations. From this comparison, we derive the CO2 column density above the 120-130 km region. [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 detailAtomic oxygen in the Martian thermosphere traced by the 130.4 and 135.6 nm emission lines with MAVEN/IUVS
Ritter, Birgit ULiege; Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege et al

Conference (2018, September)

We analyze limb observations of dayglow emissions from atomic oxygen in the upper Martian atmosphere. The data has been collected during the last almost four years by the Imaging Ultraviolet Spectrograph ... [more ▼]

We analyze limb observations of dayglow emissions from atomic oxygen in the upper Martian atmosphere. The data has been collected during the last almost four years by the Imaging Ultraviolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) spacecraft. Mean profiles for specific solar longitude, latitude and solar zenith angle ranges are created. We then use atmospheres from the Mars General Circulation models and in situ solar flux data from the MAVEN Extreme Ultraviolet Monitor (EUVM) to perform Monte Carlo and radiative transfer modeling for comparison with the observations. In order to match the results and to eventually retrieve oxygen densities, scaling factors are applied to the GCM atmospheric densities. We will present preliminary results of this analysis [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 detailAuroral storm and polar arcs at Saturn
Palmaerts, Benjamin ULiege; Radioti, Aikaterini ULiege; Grodent, Denis ULiege et al

Conference (2018, July 11)

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph (UVIS ... [more ▼]

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini observed Saturn's northern aurora for about 14h. In this final UVIS sequence, several auroral structures appear, revealing processes occurring simultaneously in Saturn's magnetosphere. A poleward expansion and a brightening of the main emission dawn arc, a phenomenon known as an auroral storm, suggests that an intense flux closure process took place in the magnetotail through magnetic reconnection. This magnetotail reconnection and the associated field dipolarization generated signatures in the auroral, magnetic field, and plasma wave data. The enhanced magnetotail reconnection is likely caused by a compression of the magnetosphere induced by the arrival at Saturn of an interplanetary coronal mass ejection. In addition to the auroral storm, a polar arc observed on the duskside was tracked for the first time from the start of its growth phase until its quasi disappearance, providing evidence of its formation process. This polar arc is a proxy for the location of reconnection sites on the dayside magnetosphere and for the orientation of the interplanetary magnetic field. Finally, the atypical observation of one of the most polar auroral arcs ever reported at Saturn supports the scenario of an interplanetary shock arriving at Saturn at the end of the Cassini mission. In that respect, the ultimate UVIS auroral sequence allowed us to capture dynamical aspects of Saturn’s magnetosphere not frequently or even never observed in the past. [less ▲]

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See detailThe polar region of Jupiter’s aurora : barcode noise, conjugate flares and more...
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gladstone, Randy et al

Conference (2018, July 11)

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 ... [more ▼]

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 nm range, to explore the polar physics in two very different ways. In the first part of this presentation, we will analyze the rapid variations of the background noise caused by >10MeV electrons penetrating the instrument. In UV images, this rapidly varying signal takes the form of a barcode-like pattern. We will discuss the mapping, the altitude and the characteristic timescale of the “barcode events” in order to constrain the mechanisms giving rise to them. In the second part, we will compare simultaneous observations of the aurorae from the two hemispheres. One dataset comes from Juno-UVS while the other comes from the Hubble Space Telescope STIS instrument. We will show that most auroral features in one hemisphere have a clear counterpart in the other one. Among other examples, we will show evidence of conjugate flares in the active region of the two hemispheres. However, other strong brightness enhancements only show up in one hemisphere, without any echo in the other one. [less ▲]

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See detailThe Largest Electron Differential Energy Flux Observed at Mars by the Mars Express Spacecraft, 2004‐2016
Frahm, R. A.; Winningham, J. D.; Coates, A. J. et al

in Journal of Geophysical Research: Space Physics (2018), 123

The goal of this paper is to understand the processes by which solar wind electrons are energized in the Martian magnetosphere and how this compares to processes at Venus and Earth. Each is unique in the ... [more ▼]

The goal of this paper is to understand the processes by which solar wind electrons are energized in the Martian magnetosphere and how this compares to processes at Venus and Earth. Each is unique in the source of its magnetic field topology and how this influences electron energization. To achieve this goal, 24 million spectra spanning 13 years have been examined using the Electron Spectrometer from the Mars Express spacecraft between about 12,000 km to about 250 km altitude, and from all latitudes and local times. The top 10 largest differential energy flux at energies above the differential energy flux peak have been found: seven spectra from the magnetosheath near noon, three from the dark tail (the largest two from the mid‐ and ionospheric edge of the magnetosheath). Spectral comparisons show a decade range in the peak of the electron distributions; however, all distributions show a similar energy maximum dictated by solar wind/planet interaction. Similarly derived, the largest Venus spectrum occurred near the magnetosheath bow shock and had the same shape as the most intense Mars inner magnetosheath spectrum. The Mars and Venus dayside spectra compared to the Mars nightside spectrum that included an enhanced optical signal attributed to discrete “auroral” precipitation show a similar shape. These spectra are also compared to a selected auroral zone electron spectra from the Earth. The Mars and Venus results suggest that there is no more energy needed to generate electrons forming the nightside precipitation than is gained during the solar wind/planet interaction. [less ▲]

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See detailCassini UVIS Observations of Saturn's Auroras and Polar Haze
Pryor, W.R.; West, R.A.; Jouchoux, A. et al

Poster (2018, July)

In 2016 and 2017, the Cassini Saturn Orbiter executed a final series of high inclination, low- periapsis orbits ideal for studying Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph ... [more ▼]

In 2016 and 2017, the Cassini Saturn Orbiter executed a final series of high inclination, low- periapsis orbits ideal for studying Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) obtained an extensive set of auroral images of both poles, some at the highest spatial resolution obtained during Cassini's long orbital mission (2004-2017). In some cases, two or three spacecraft slews at right angles to the long slit of the spectrograph were required to cover the entire auroral region to form images of auroral H2 and H emission. The long wavelength part of the northern UVIS polar images contains a signal from reflected sunlight with absorption signatures of acetylene and other Saturn hydrocarbons. Saturn's UV-dark polar hexagon is now seen in the new UVIS long- wavelength data, surrounded by a circular collar that is less dark. There is a definite spatial relationship between the UV-bright auroras and the dark material, with the dark material concentrated under or just inside of the main auroral oval. The outer dark collar roughly corresponds with the previously reported weaker outer auroral oval (Grodent et al., 2011; Lamy et al., 2013). Time variations in the dark material are seen. The spectroscopy of the different regions will be discussed. As has been previously discussed using Voyager data (Lane et al., 1982, West et al., 1983, Pryor and Hord, 1991), Hubble data (Ben Jaffel et al., 1995; Gerard et al., 1995) and Cassini data (Sayanagi et al., 2018), Saturn's auroras appear to be generating, through both neutral and ion chemistry, UV-dark material that is probably composed of complex hydrocarbons. [less ▲]

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See detailCombined Juno observations and modeling of the Jovian auroral electron interaction with the Jovian upper atmosphere
Gérard, Jean-Claude ULiege; Bonfond, Bertrand; Gladstone, G.R. et al

Poster (2018, July)

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s ... [more ▼]

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s magnetic footprint. In addition, the ratio of the H2 spectral band absorbed by hydrocarbons to the unabsorbed portion of the spectrum (FUV color ratio) is often used as a proxy for the depth of the penetration of energetic electrons (relative to the hydrocarbon homopause). The relationship between the color ratio and the electron penetration has been simulated with a Monte Carlo model solving the Boltzmann transport equation. Analysis of concurrent FUV and IR images obtained during the first perijove (PJ1) suggests that the ratio of H3+ radiance to H2 unabsorbed emission is maximal in regions with low FUV color ratio. This result suggests that part of the H3+ column is lost in reactions with methane which converts H3+ into heavier ions. We also examine the observed relationship between the detailed morphology of the ultraviolet structures and of the associated UV color ratio, the total downward electron energy flux and its spectral characteristics. [less ▲]

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See detailJuno-UVS observation of the Io footprint
Hue, V.; Greathouse, T. K.; Bonfond, Bertrand ULiege et al

Poster (2018, July)

The perijove observations performed by Juno-UVS nominally range from -5 hours up to +5 hours about perijove, during which Juno’s distance to Jupiter ranges from 7 RJ down to 1.05 RJ. The Io footprints are ... [more ▼]

The perijove observations performed by Juno-UVS nominally range from -5 hours up to +5 hours about perijove, during which Juno’s distance to Jupiter ranges from 7 RJ down to 1.05 RJ. The Io footprints are a characterization of the complex electrodynamic interaction generated at Io and modulated by the inner magnetosphere of Jupiter. Previous observations with the Hubble Space Telescope allowed the characterization of the footprints as a function of Io’s centrifugal latitude, despite observational bias that Earth-based observers are subject to. Juno’s unique vantage point in the Jovian system removes these biases allowing UVS access to the full range of centrifugal latitudes and all possible local time geometries. We will present our investigation of the local time variability in Io’s footprint emitted power and color ratio, including observations of the footprints while Io was in eclipse. [less ▲]

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See detailJupiter’s mesmerizing auroral show (PJ13); HST ultraviolet observations near and far from Juno perijoves
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Palmaerts, Benjamin ULiege et al

Conference (2018, July)

After a 6-month period during which the separation angle between the Sun and Jupiter was too small to permit observations with Earth orbit telescopes, operation of the Hubble Space Telescope, supporting ... [more ▼]

After a 6-month period during which the separation angle between the Sun and Jupiter was too small to permit observations with Earth orbit telescopes, operation of the Hubble Space Telescope, supporting the Juno mission, was resumed (almost) in time for PJ11. We briefly review the main results of the previous part of this HST campaign, covering PJ03 to PJ07. We then present the newest results obtained during PJ11, PJ12 and PJ13. Most of the observing time allocated to this HST campaign was used during the first part of the campaign and allowed us to sample Jupiter’s aurora, not only near Juno’s perijoves, but also during the week before and the week after each perijove. During these times away from perijove, HST-STIS was the sole instrument able to provide high spatial and high temporal resolution dynamic images of Jupiter’s FUV aurora, which can be compared with measurements from Juno’s in situ instruments. Instead of presenting a statistical overview of the data, we have a more detailed look at some specific features revealed by the as yet unsurpassed STIS camera. In particular, we identify distinctive auroral phenomena, like explosive brightenings poleward of the main auroral emission. We present one such event, which we link to a strong perturbation of the magnetic field and of the energy distribution of the plasma particles concurrently observed with Juno. We suggest that the characteristics and the timing of this perturbation and of its associated auroral signature are consistent with a reconnection event. [less ▲]

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See detailMonte Carlo Simulations of the Interaction of Fast Proton and Hydrogen Atoms With the Martian Atmosphere and Comparison With In Situ Measurements
Bisikalo, D.V.; Shematovich, V.; Gérard, Jean-Claude ULiege et al

in Journal of Geophysical Research. Space Physics (2018), 123

We present model results of the interaction of proton and hydrogen atom precipitation with the Martian atmosphere. We use a kinetic Monte Carlo model developed earlier for the analysis of the Analyzer of ... [more ▼]

We present model results of the interaction of proton and hydrogen atom precipitation with the Martian atmosphere. We use a kinetic Monte Carlo model developed earlier for the analysis of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) Mars Express data. With the availability of MarsAtmosphere and Volatile Evolution Mission in situ measurements, not only the flux of protons incident on theatmosphere but also their degradation along the orbit may now be described. The comparison of thesimulations with data collected with the Solar Wind Ion Analyzer shows that the Monte Carlo modelreproduces some of the measured features. The results of comparison between simulations andmeasurements of the proton fluxes at low altitudes make it possible to infer the efficiency of chargeexchange between solar wind and the extended hydrogen corona if the value of the magnetic field ismeasured simultaneously. We also find that the induced magnetic field plays a very important role in theformation of the backscattered flux and strongly controls its magnitude. At the same time, discrepancies between the modeled and the measured energy spectra of the backscattered protons are pointed out. We suggest that some of the physical processes controlling the upward flux are not fully understood or that the data processing of the measured backscattered proton flux should be improved [less ▲]

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See detailIn-flight characterization and calibration of the Juno-Ultraviolet Spectrograph (Juno-UVS)
Hue, V.; Kammer, J. D.; Gladstone, G. R. et al

in Proceedings of SPIE : The International Society for Optical Engineering (2018, June)

The Juno mission, orbiting Jupiter since July 2016, offers an unprecedented opportunity to study Jupiter, from its internal structure to its magnetospheric environment. Juno-UVS is a ultraviolet (UV ... [more ▼]

The Juno mission, orbiting Jupiter since July 2016, offers an unprecedented opportunity to study Jupiter, from its internal structure to its magnetospheric environment. Juno-UVS is a ultraviolet (UV) photon counting spectrograph with a bandpass of 68<λ<210 nm. The main purpose of Juno-UVS is to observe and characterize Jupiter’s UV auroral emissions and provide global context for Juno’s in-situ particles and fields instruments. Juno is a spinning spacecraft that nominally spins at 2 rpm, so it spends a significant amount of time observing the sky background, including stars, interplanetary medium and extragalactic sources. We present here how we use this information to: (i) characterize and calibrate Juno-UVS; and (ii) monitor the detector response over the mission. [less ▲]

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See detailCo-Rotating Magnetic Reconnection Site in Saturn's Magnetosphere
Yao, Zhonghua ULiege; Coates, A.; Ray, L. et al

Poster (2018, June)

Using measurements from the Cassini spacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of co-rotating reconnection site, which can only be driven by an internally generated source. Our ... [more ▼]

Using measurements from the Cassini spacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of co-rotating reconnection site, which can only be driven by an internally generated source. Our results demonstrate that the co-rotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphere, and consequently produce Fermi acceleration of electrons. This reconnection site lasted for longer than one Saturn’s rotation period. The long-lasting and co-rotating natures of magnetic reconnection site at Saturn suggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics (e.g., the auroral precipitation) from the Earth. Our co-rotating reconnection picture could also potentially shed light on the fast rotating magnetized plasma environments in the solar system and beyond. [less ▲]

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See detailJuno/JIRAM Observations of Jupiter’s Main Aurorae and Satellite Footprints.
Mura, A.; Adriani, A.; Connerney, J. E. P. et al

Conference (2018, June)

JIRAM (Jovian Infrared Auroral Mapper) on board the NASA/Juno spacecraft is an imaging /spectrometer in the 2-5 um range. One of the imager channels (L band 3.3-3.6 um) is designed to study the Jovian H3 ... [more ▼]

JIRAM (Jovian Infrared Auroral Mapper) on board the NASA/Juno spacecraft is an imaging /spectrometer in the 2-5 um range. One of the imager channels (L band 3.3-3.6 um) is designed to study the Jovian H3+ auroral emission. The very good angular resolution of the camera, combined with the unique vantage point provided by Juno, allows to JIRAM to observe the aurorae with unprecedented details. Here we present the results of ~2 years of auroral observations, with particular emphasis  on the auroral footprints of the Galilean moons. These are bright spots (with associated tail) that appear in Jupiter’s ionosphere at the base of the magnetic field lines that sweep past Io, Europa, and Ganymede. The moons are obstacles in the path of Jupiter’s rapidly rotating magnetospheric plasma and the resulting electromagnetic interaction launches Alfvén waves along the magnetic field towards Jupiter, where intense electron bombardment of the hydrogen atmosphere causes it to glow. Recent observations reveal for the first time that the footprint of Io is comprised of a regularly spaced array of emission features, extending downstream of the leading footprint, resembling a repeating pattern of swirling vortices (von Kármán vortex street) shed by a cylinder in the path of a flowing fluid. Contrary to the larger spots seen in the UV, the small scale of these multiple features (~100 km) is incompatible with the simple paradigm of multiple Alfvén wave reflections. The small scale of these multiple features (~100 km) shows that this particular multiplicity is not generated by multiple Alfven wave reflections. Observations of Io’s trailing tail well downstream of the leading feature reveal a pair of closely spaced parallel arcs that were previously unresolved. Both of Ganymede’s footprint spots (main and secondary) appear as a pair of emission features that evidently provides a remote measure of Ganymede’s magnetosphere, mapped from its distant orbit onto Jupiter’s ionosphere. [less ▲]

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