Publications of Denis Grodent
Bookmark and Share    
Full Text
See detailA Statistical Survey of Low Frequency Magnetic Fluctuations at Saturn
Pan, Dong-Xiao; Yao, Zhong-Hua; Guo, Rui-Long et al

in Journal of Geophysical Research. Space Physics (2021), 126(2), 28387

Low-frequency waves are closely related to magnetospheric energy dissipation processes. The Cassini spacecraft explored Saturn's magnetosphere for over 13 years, until September 2017, covering a period of ... [more ▼]

Low-frequency waves are closely related to magnetospheric energy dissipation processes. The Cassini spacecraft explored Saturn's magnetosphere for over 13 years, until September 2017, covering a period of more than a complete solar cycle. Using this rich heritage data set, we systematically investigated key physical parameters of low-frequency waves in Saturn's magnetosphere, including their local time distribution and the dependence on solar activity. We found that the wave activity peaked in the near noon sector. For the nightside, the wave intensity also appeared to peak pre and postmidnight. Due to the limited local time coverage for each solar phase, we were not able to draw a firm conclusion on the wave's dependence on solar activity. In general, the wave power showed a monotonically decreasing trend toward larger distances in nightside sectors especially during the declining phase, which implied that low-frequency waves mainly originate from the relatively inner regions of the magnetosphere. On the dayside, stronger waves were mostly located at/within ∼25 Rs, near the magnetopause. The study shows a global picture of low-frequency waves in Saturn's magnetosphere, providing important implications for how magnetospheric energy dissipates into Saturn's polar ionosphere and atmosphere. [less ▲]

Detailed reference viewed: 22 (3 ULiège)
Full Text
See detailJupiter's X-ray aurora during a mass injection and Io mass loading events observed by XMM-Newton, Hubble, and Hisaki
Wibisono, Affelia; Branduardi-Raymont, Graziella; Dunn, Will et al

in EGU General Assembly Conference Abstracts (2021)

Voyager 1 detected the first extra-terrestrial UV auroral emissions when it explored the Jupiter system in 1979 while the planet’s X-ray aurora was discovered later that year by the Einstein Observatory ... [more ▼]

Voyager 1 detected the first extra-terrestrial UV auroral emissions when it explored the Jupiter system in 1979 while the planet’s X-ray aurora was discovered later that year by the Einstein Observatory. Electrons are accelerated into Jupiter’s atmosphere near the poles and excite native molecular and atomic hydrogen. These then release UV photons after returning to the ground state. The same population of precipitating electrons can also emit high energy (>2 keV) X-ray photons by bremsstrahlung to produce Jupiter’s hard X-ray aurora. At higher latitudes and within the oval of UV and hard X-ray emissions is where the more diffuse UV and low energy (<2 keV) soft X-ray aurorae are found. Charge exchange processes between precipitating ions and neutrals in the gas giant planet’s atmosphere are responsible for the soft X-ray emissions. Simultaneous observations of Jupiter’s UV and X-ray aurorae were carried out by the Hubble Space Telescope (HST), Hisaki satellite and XMM-Newton in September 2019 to support Juno’s 22nd perijove. Images of the northern far UV aurora by HST showed internally driven dawn storms and injection events occurring at least twice during the observation period. These features are thought to be caused by magnetic reconnection happening in the middle magnetosphere. This subsequently leads to the dipolarization of the field lines which injects hot magnetospheric plasma from the middle to the inner magnetosphere. Hisaki saw an impulsive brightening in the Io plasma torus on the day of the second event showing that there was indeed a large-scale injection that penetrated the central torus in the inner magnetosphere. At this time, the northern aurora brightened in both extreme UV and hard X-ray, which suggests that there was an increase in electron precipitation. There was no response from the soft X-ray aurora, and no quasi-periodic pulsations, often observed in the auroral emissions, were detected during either of the events. X-ray spectral analysis reveals that the precipitating ions were iogenic. We conclude that we have witnessed two cases of mass injection in the Jovian inner magnetosphere due to Io mass loading events. [less ▲]

Detailed reference viewed: 25 (3 ULiège)
Full Text
See detailHow Jupiter’s unusual magnetospheric topology structures its aurora
Zhang, Binzheng; Delamere, Peter A.; Yao, Zhonghua ULiege et al

in Science Advances (2021), 7(15), 1204

Jupiter’s bright persistent polar aurora and Earth’s dark polar region indicate that the planets’ magnetospheric topologies are very different. High-resolution global simulations show that the ... [more ▼]

Jupiter’s bright persistent polar aurora and Earth’s dark polar region indicate that the planets’ magnetospheric topologies are very different. High-resolution global simulations show that the reconnection rate at the interface between the interplanetary and jovian magnetic fields is too slow to generate a magnetically open, Earth-like polar cap on the time scale of planetary rotation, resulting in only a small crescent-shaped region of magnetic flux interconnected with the interplanetary magnetic field. Most of the jovian polar cap is threaded by helical magnetic flux that closes within the planetary interior, extends into the outer magnetosphere, and piles up near its dawnside flank where fast differential plasma rotation pulls the field lines sunward. This unusual magnetic topology provides new insights into Jupiter’s distinctive auroral morphology. Jupiter’s slow dayside magnetic merging and fast rotation produce an unusual magnetic topology that can explain its polar aurora. Jupiter’s slow dayside magnetic merging and fast rotation produce an unusual magnetic topology that can explain its polar aurora. [less ▲]

Detailed reference viewed: 26 (1 ULiège)
Full Text
See detailAre Dawn Storms Jupiter's Auroral Substorms?
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Gladstone, G. R. et al

in AGU Advances (2021), 2(1), 2020000275

Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here, we show for ... [more ▼]

Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here, we show for the first time global views of the phenomenon, from its initiation to its end and from the nightside of the aurora onto the dayside. Based on Juno's first 20 orbits, some patterns now emerge. Small short-lived spots are often seen a couple of hours before the main emission starts to brighten and evolve from a straight arc to a more irregular one in the midnight sector. As the whole feature rotates dawn-ward, the arc then separates into two arcs with a central initially void region that is progressively filled with emissions. A gap in longitude then often forms before the whole feature dims. Finally, it transforms into an equatorward-moving patch of auroral emissions associated with plasma injection signatures. Some dawn storms remain weak and never fully develop. We also found cases of successive dawn storms within a few hours. Dawn storms thus share many fundamental features with the auroral signatures of the substorms at Earth, despite the substantial differences between the dynamics of the magnetosphere at the two planets. [less ▲]

Detailed reference viewed: 34 (6 ULiège)
Full Text
See detailJupiter's aurora liveliness during solar minimum
Palmaerts, Benjamin ULiege; Grodent, Denis ULiege; Bonfond, Bertrand ULiege et al

Conference (2020, September)

Detailed reference viewed: 29 (6 ULiège)
Full Text
See detailSpatial Distribution of the Pedersen Conductance in the Jovian Aurora From Juno‐UVS Spectral Images
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Bonfond, Bertrand ULiege et al

in Journal of Geophysical Research. Space Physics (2020), 125

Ionospheric conductivity perpendicular to the magnetic field plays a crucial role in the electrical coupling between planetary magnetospheres and ionospheres. At Jupiter, it controls the flow of ... [more ▼]

Ionospheric conductivity perpendicular to the magnetic field plays a crucial role in the electrical coupling between planetary magnetospheres and ionospheres. At Jupiter, it controls the flow of ionospheric current from above and the closure of the magnetosphere‐ionosphere circuit in the ionosphere. We use multispectral images collected with the Ultraviolet Spectral (UVS) imager on board Juno to estimate the two‐dimensional distribution of the electron energy flux and characteristic energy. These values are fed to an ionospheric model describing the generation and loss of different ion species, to calculate the auroral Pedersen conductivity. The vertical distributions of H3+, hydrocarbon ions, and electrons are calculated at steady state for each UVS pixel to characterize the spatial distribution of electrical conductance in the auroral region. We find that the main contribution to the Pedersen conductance stems from collisions of H3+and heavier ions with H2. However, hydrocarbon ions contribute as much as 50% to Σp when the auroral electrons penetrate below the homopause. The largest values are usually associated with the bright main emission, the Io auroral footprint and occasional bright emissions at high latitude. We present examples of maps for both hemispheres based on Juno‐UVS images, with Pedersen conductance ranging from less than 0.1 to a few mhos. [less ▲]

Detailed reference viewed: 47 (17 ULiège)
Full Text
See detailSix Pieces of Evidence Against the Corotation Enforcement Theory to Explain the Main Aurora at Jupiter
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Grodent, Denis ULiege

in Journal of Geophysical Research: Space Physics (2020), 125(11), 2020028152

The most remarkable feature of the ultraviolet auroras at Jupiter is the ever-present and almost continuous curtain of bright emissions centered on each magnetic pole and called the main emissions ... [more ▼]

The most remarkable feature of the ultraviolet auroras at Jupiter is the ever-present and almost continuous curtain of bright emissions centered on each magnetic pole and called the main emissions. According to the widely accepted theory, it results from an electric current loop transferring momentum from the Jovian ionosphere to the magnetospheric plasma. However, predictions based on this theory have been recently challenged by observations from Juno and the Hubble Space Telescope. Here we review the main contradictory observations, expose their implications for the theory, and discuss promising paths forward. [less ▲]

Detailed reference viewed: 24 (7 ULiège)
Full Text
See detailSix observational pieces of evidence against corotation as the main cause for the aurora at Jupiter
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Grodent, Denis ULiege

Conference (2020)

The Main Emissions are the most recognizable feature of the aurorae at Jupiter and they are responsible for roughly 1/3rd of the total emitted power. They form an ever-present and quasi-continuous ring of ... [more ▼]

The Main Emissions are the most recognizable feature of the aurorae at Jupiter and they are responsible for roughly 1/3rd of the total emitted power. They form an ever-present and quasi-continuous ring of emission centered on the magnetic poles. The most widely accepted explanation for these auroral emissions involves a current system related to the corotation enforcement of the plasma in the Jovian magnetosphere. Models based on this theory explain many characteristics of the aurorae. However, recent observations from the NASA Juno spacecraft and the ESA/NASA Hubble Space Telescope, complemented by previous results from the NASA Galileo spacecraft, challenge this theoretical framework. In this presentation, we will review six specific sets of observations contradictory with expectations from the corotation enforcement theory. We will expose their implications for the modelling of the Jovian magnetosphere and aurorae and we will discuss promising paths forward. [less ▲]

Detailed reference viewed: 20 (1 ULiège)
Full Text
See detailA long-lasting auroral spiral rotating around Saturn’s pole
Palmaerts, Benjamin ULiege; Yao, Zhonghua ULiege; Sergis, N. et al

in Geophysical Research Letters (2020)

The main ultraviolet auroral emission at Saturn consists of multiple structures forming a discontinuous ring of emission around the poles, occasionally organized in a global spiral. We present continuous ... [more ▼]

The main ultraviolet auroral emission at Saturn consists of multiple structures forming a discontinuous ring of emission around the poles, occasionally organized in a global spiral. We present continuous observation of an auroral spiral rotating at ~85% of rigid corotation during several hours. Simultaneously, energetic neutral atom (ENA) emissions revealed a hot magnetospheric plasma population located in the same local time sector as the ends of the rotating spiral. Following plasma theory, we propose that pressure gradients induced by the energized plasma distorted the magnetospheric current system, resulting in the spiral morphology of the aurora. The rotating hot plasma was several times re-energized in the dusk sector during at least two days, generating a long-lasting auroral spiral. The ultraviolet spiral, the ENA emissions and the ions revealed by this multi-instrument dataset are three signatures of a magnetosphere-ionosphere coupling current system and of the associated hot plasma population rotating around Saturn. [less ▲]

Detailed reference viewed: 25 (3 ULiège)
Full Text
See detailReconnection- and Dipolarization-Driven Auroral Dawn Storms and Injections
Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege; Clark, G. et al

in Journal of Geophysical Research: Space Physics (2020), 125(8),

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the ... [more ▼]

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the observations is a coincidence or part of an underlying physical connection. We show six clear examples from a recent Hubble Space Telescope campaign (GO-14634) that each display both auroral dawn storms and auroral injection signatures. We found that these conjugate phenomena could exist during intervals of either relatively low or high auroral activity, as evidenced by the varied levels of total auroral power. In situ observations of the magnetosphere by Juno show a strong magnetic reconnection event inside of 45 Jupiter radii (RJ) on the predawn sector, followed by two dipolarization events within the following 2 hr, coincident with the auroral dawn storm and auroral injection event. We therefore suggest that the auroral dawn storm is the manifestation of magnetic reconnection in the dawnside magnetosphere. The dipolarization region is mapped to the auroral injection, strongly suggesting that this was associated with the auroral injection. Since magnetic reconnection and dipolarization are physically connected, we therefore suggest that the often-conjugate auroral dawn storm and auroral injection events are also physically connected consequences. ©2020. The Authors. [less ▲]

Detailed reference viewed: 28 (5 ULiège)
Full Text
See detailAn Enhancement of Jupiter's Main Auroral Emission and Magnetospheric Currents
Nichols, J. D.; Allegrini, F.; Bagenal, F. et al

in Journal of Geophysical Research: Space Physics (2020), 125(8),

We present observations of Jupiter's magnetic field and plasma obtained with the NASA Juno spacecraft during February 2018, along with simultaneous Hubble Space Telescope (HST) observations of the planet ... [more ▼]

We present observations of Jupiter's magnetic field and plasma obtained with the NASA Juno spacecraft during February 2018, along with simultaneous Hubble Space Telescope (HST) observations of the planet's auroras. We show that a few-day transient enhancement of the azimuthal and radial magnetic fields and plasma temperature was coincident with a significant brightening of Jupiter's dawn-side main auroral emission. This presents the first evidence of control of Jupiter's main auroral emission intensity by magnetosphere-ionosphere coupling currents. We support this association by self-consistent calculation of the magnetosphere-ionosphere coupling and radial force balance currents using an axisymmetric model, which broadly reproduces the Juno magnetic field and plasma observations and the HST auroral observations. We show that the transient enhancement can be explained by increased hot plasma pressure in the magnetosphere together with increased iogenic plasma mass outflow rate. Overall, this work provides important observational and modeling evidence revealing the behavior of Jupiter's giant magnetosphere. ©2020. American Geophysical Union. All Rights Reserved. [less ▲]

Detailed reference viewed: 19 (5 ULiège)
Full Text
See detailAn attempt to detect transient changes in Io's SO2 and NaCl atmosphere
Roth, L.; Boissier, J.; Moullet, A. et al

in Icarus (2020), 350

Io's atmosphere is predominately SO2 that is sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere ... [more ▼]

Io's atmosphere is predominately SO2 that is sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere. Numerous previous studies attributed various transient phenomena in Io's environment and Jupiter's magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far. Here we report four observations of atmospheric SO2 and NaCl from the same hemisphere of Io, obtained with the IRAM NOEMA interferometer on 11 December 2016, 14 March, 6 and 29 April 2017. These observations are compared to measurements of volcanic hot spots and Io's neutral and plasma environment. We find a stable NaCl column density in Io's atmosphere on the four dates. The SO2 column density derived for December 2016 is about 30% lower compared to the SO2 column density found in the period of March to April 2017. This increase in SO2 from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO2 ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO2 abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a rather quiescent state, preventing further conclusions. Only Jupiter's aurora morphology underwent several short-term changes, which are apparently unrelated to Io's quiescent environment or the relatively stable atmosphere. © 2020 The Authors [less ▲]

Detailed reference viewed: 14 (3 ULiège)
Full Text
See detailTemporal and Spectral Studies by XMM-Newton of Jupiter's X-ray Auroras During a Compression Event
Wibisono, A. D.; Branduardi-Raymont, G.; Dunn, W. R. et al

in Journal of Geophysical Research: Space Physics (2020), 125(5),

We report the temporal and spectral results of the first XMM-Newton observation of Jupiter's X-ray auroras during a clear magnetospheric compression event on June 2017 as confirmed by data from the Jovian ... [more ▼]

We report the temporal and spectral results of the first XMM-Newton observation of Jupiter's X-ray auroras during a clear magnetospheric compression event on June 2017 as confirmed by data from the Jovian Auroral Distributions Experiment (JADE) instrument onboard Juno. The northern and southern auroras were visible twice and thrice respectively as they rotated in and out of view during the ∼23-hr (almost 2.5 Jupiter rotations) long XMM-Newton Jovian-observing campaign. Previous auroral observations by Chandra and XMM-Newton have shown that the X-ray auroras sometimes pulse with a regular period. We applied wavelet and fast Fourier transforms (FFTs) on the auroral light curves to show that, following the compression event, the X-ray auroras exhibited a recurring 23- to 27-min periodicity that lasted over 12.5 hr (longer than a Jupiter rotation). This periodicity was observed from both the northern and southern auroras, suggesting that the emission from both poles was caused by a shared driver. The soft X-ray component of the auroras is due to charge exchange processes between precipitating ions and neutrals in Jupiter's atmosphere. We utilized the Atomic Charge Exchange (ACX) spectral package to produce solar wind and iogenic plasma models to fit the auroral spectra in order to identify the origins of these ions. For this observation, the iogenic model gave the best fit, which suggests that the precipitating ions are from iogenic plasma in Jupiter's magnetosphere. ©2020. The Authors. [less ▲]

Detailed reference viewed: 14 (4 ULiège)
Full Text
See detailPossible Transient Luminous Events Observed in Jupiter's Upper Atmosphere
Giles, Rohini S.; Greathouse, Thomas K.; Bonfond, Bertrand ULiege et al

in Journal of Geophysical Research: Planets (2020), 125(11), 2020006659

Abstract Eleven transient bright flashes were detected in Jupiter's atmosphere using the ultraviolet spectrograph instrument on the Juno spacecraft. These bright flashes are only observed in a single spin ... [more ▼]

Abstract Eleven transient bright flashes were detected in Jupiter's atmosphere using the ultraviolet spectrograph instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ∼1.4 ms. The spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 260 km above the 1-bar level. Based on these characteristics, we suggest that these are observations of transient luminous events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that occur in the Earth's upper atmosphere in response to tropospheric lightning strikes. This is supported by visible light imaging, which shows cloud features typical of lightning source regions at the locations of several of the bright flashes. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on Jupiter. [less ▲]

Detailed reference viewed: 33 (7 ULiège)
Full Text
See detailFlying through a dawn storm: a multi-instrument study of the traversal of a dawn storm by Juno on February 7th 2018
Bonfond, Bertrand ULiege; Guo, Ruilong ULiege; Yao, Zhonghua ULiege et al

Conference (2020)

On February 7th 2018, during Juno’s 11th perijove observation sequence, Juno’s ultraviolet spectrograph (Juno-UVS) unveiled the development of a dawn storm in Jupiter's aurorae. These auroral events ... [more ▼]

On February 7th 2018, during Juno’s 11th perijove observation sequence, Juno’s ultraviolet spectrograph (Juno-UVS) unveiled the development of a dawn storm in Jupiter's aurorae. These auroral events consist of spectacular brightenings of the midnight to dawn sector of the main emissions at Jupiter. At the end of the sequence, Juno crossed the magnetic field lines connected to this dawn storm, unraveling some of the processes giving rise to these spectacular events. All in situ instruments detected a sharp transition as the spacecraft entered the dawn storm at an altitude of approximately 5RJ in the southern hemisphere. The particle fluxes detected by the JADE and JEDI instruments, including electrons and ions, increased dramatically. A strong flux of penetrating radiation was also detected by the UVS instrument. The Alfvén waves spectrograms derived from the MAG instrument also show a clear transition between a quiet and an extremely active regime as the spacecraft entered the dawn storm. Furthermore, the orientation of the magnetic field showed a very strong perturbation, associated with intense currents. And, finally, intense bKOM emissions were also observed during this time interval. Combined with the remote sensing observations of the aurora, these datasets strongly suggest that Juno witnessed a strong magnetospheric reconfiguration that started in the magneto-tail and then evolved toward dawn as the planet rotated. [less ▲]

Detailed reference viewed: 27 (6 ULiège)
Full Text
See detailAuroral Beads at Saturn and the Driving Mechanism: Cassini Proximal Orbits
Radioti, Aikaterini ULiege; Yao, Zhonghua ULiege; Grodent, Denis ULiege et al

in Astrophysical Journal (2019), 885

During the Grand Finale Phase of Cassini, the Ultraviolet Imaging Spectrograph on board the spacecraft detected repeated detached small- scale auroral structures. We describe these structures as auroral ... [more ▼]

During the Grand Finale Phase of Cassini, the Ultraviolet Imaging Spectrograph on board the spacecraft detected repeated detached small- scale auroral structures. We describe these structures as auroral beads, a term introduced in the terrestrial aurora. Those on DOY 232 2017 are observed to extend over a large range of local times, i.e., from 20 LT to 11 LT through midnight. We suggest that the auroral beads are related to plasma instabilities in the magnetosphere, which are often known to generate wavy auroral precipitations. Energetic neutral atom enhancements are observed simultaneously with auroral observations, which are indicative of a heated high pressure plasma region. During the same interval we observe conjugate periodic enhancements of energetic electrons, which are consistent with the hypothesis that a drifting interchange structure passed the spacecraft. Our study indicates that auroral bead structures are common phenomena at Earth and giant planets, which probably demonstrates the existence of similar fundamental magnetospheric processes at these planets. [less ▲]

Detailed reference viewed: 33 (7 ULiège)
Full Text
See detailJovian dawn storms and terrestrial auroral substorms: similarities and differences
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Gladstone, Randy et al

Conference (2019, September 18)

Juno's polar orbit allows us to contemplate a complete view of the Jovian aurorae for the first time. Here we mainly use observations from the ultraviolet spectrograph (Juno-UVS) in order to study one of ... [more ▼]

Juno's polar orbit allows us to contemplate a complete view of the Jovian aurorae for the first time. Here we mainly use observations from the ultraviolet spectrograph (Juno-UVS) in order to study one of the most spectacular features of Jupiter's aurorae: the dawn storms. Many of the properties of the dawn storms observed by Juno-UVS are similar to those of terrestrial substorms. [less ▲]

Detailed reference viewed: 58 (6 ULiège)
Full Text
See detailRecent Juno-UVS Observations of Jupiter's Auroras
Gladstone, Randy; Greathouse, Thomas; Versteeg, Maarten et al

Conference (2019, September 18)

Juno’s polar orbit provides excellent vantage pointsfor studying Jupiter’s bright and highly-variable far-ultraviolet (FUV) auroral emissions [1-3]. The Juno mission is a little over halfway through its ... [more ▼]

Juno’s polar orbit provides excellent vantage pointsfor studying Jupiter’s bright and highly-variable far-ultraviolet (FUV) auroral emissions [1-3]. The Juno mission is a little over halfway through its primary mission, and here we review some of the interesting results found so far by the Ultraviolet Spectrograph (UVS) instrument [4] during perijoves 1 and 3-21. [less ▲]

Detailed reference viewed: 42 (1 ULiège)
Full Text
See detailCassini UVIS Detection of Saturn's North Polar Hexagon in the Grand Finale Orbits
Pryor, W. R.; Esposito, L. W.; Jouchoux, A. et al

in Journal of Geophysical Research. Planets (2019), 124

Cassini's final orbits in 2016 and 2017 provided unprecedented spatial resolution of Saturn's polar regions from near-polar spacecraft viewing geometries. Long-wavelength channels of Cassini's Ultraviolet ... [more ▼]

Cassini's final orbits in 2016 and 2017 provided unprecedented spatial resolution of Saturn's polar regions from near-polar spacecraft viewing geometries. Long-wavelength channels of Cassini's Ultraviolet Imaging Spectrograph instrument detected Saturn's UV-dark north polar hexagon near 180 nm at planetocentric latitudes near 75°N. The dark polar hexagon is surrounded by a larger, less UV-dark collar poleward of planetocentric latitude 65°N associated with the dark north polar region seen in ground-based images. The hexagon is closely surrounded by the main arc of Saturn's UV aurora. The UV-dark material was locally darkest on one occasion (23 January 2017) at the boundary of the hexagon; in most Ultraviolet Imaging Spectrograph images the dark material more uniformly fills the hexagon. The observed UV-dark stratospheric material may be a hydrocarbon haze produced by auroral ion-neutral chemistry at submicrobar pressure levels. Ultraviolet Imaging Spectrograph polar observations are sensitive to UV-absorbing haze particles at pressures lower than about 10-20 mbar. [less ▲]

Detailed reference viewed: 22 (3 ULiège)
Full Text
See detailJuno-UVS Observation of the Io Footprint During Solar Eclipse
Hue, V.; Greathouse, T. K.; Bonfond, Bertrand ULiege et al

in Journal of Geophysical Research (Space Physics) (2019), 124

The two main ultraviolet-signatures resulting from the Io-magnetosphere interaction are the local auroras on Io's atmosphere, and the Io footprints on Jupiter. We study here how Io's daily eclipses affect ... [more ▼]

The two main ultraviolet-signatures resulting from the Io-magnetosphere interaction are the local auroras on Io's atmosphere, and the Io footprints on Jupiter. We study here how Io's daily eclipses affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfvén wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph (UVS) on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable data sets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, that is, in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvénic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfvén wings in addition to the Poynting flux generated at Io control the footprint luminosity. <P /> [less ▲]

Detailed reference viewed: 27 (4 ULiège)