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Characterising injection signatures in Jupiter's ultraviolet aurora using Juno observations
Authors:
Linus Head,
Denis Grodent,
Bertrand Bonfond,
Alessandro Moirano,
Guillaume Sicorello,
Julie Vinesse,
Alyssa Mouton,
Maïté Dumont,
Thomas Greathouse,
Vincent Hue,
Ali Sulaiman,
Barry Mauk,
Zhonghua Yao,
Ruilong Guo,
Jinyan Zhao
Abstract:
Discrete features in Jupiter's ultraviolet aurora have been interpreted as signatures of plasma injections in the middle magnetosphere. There exists some ambiguity whether magnetodisc scattering or high-latitude Alfvenic acceleration best describes the observed properties of these injection signatures, and also to what extent arcs in the outer emission are related to injections. Many injection sig…
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Discrete features in Jupiter's ultraviolet aurora have been interpreted as signatures of plasma injections in the middle magnetosphere. There exists some ambiguity whether magnetodisc scattering or high-latitude Alfvenic acceleration best describes the observed properties of these injection signatures, and also to what extent arcs in the outer emission are related to injections. Many injection signatures are the result of the evolution of dawn storms; there is, however, limited evidence that non-dawn-storm injection signatures are sometimes present in the aurora. We use automatic detection of these discrete features, alongside data from Juno-UVS and in-situ measurements by other Juno instruments, to show that scattering likely accounts for most of the electron precipitation associated with injection signatures. Additionally, there is evidence that injection signatures can be classified into two types: dawn-storm and non-dawn-storm. Arc-like features in the outer emission show very similar properties to traditional blob-like injection signatures and may consist of sequences of injection signatures that have broadened into an arc via energy-dependent electron drift.
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Submitted 17 December, 2025;
originally announced December 2025.
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Spatial variability of CH4 and C2H2 absorptions in Jupiter's auroral regions from Juno-UVS observations
Authors:
J. Vinesse,
B. Bonfond,
B. Benmahi,
A. Moirano,
D. Grodent,
T. K. Greathouse,
V. Hue,
G. Sicorello,
L. A. Head,
G. R. Gladstone,
M. W. Davis
Abstract:
Color ratios derived from molecular hydrogen emissions provide valuable diagnostics for the energy of precipitating electrons and the structure of the auroral atmosphere. We aim to characterize the horizontal and vertical variability of hydrocarbon absorption in Jupiter's auroral atmosphere using ultraviolet data from the Juno-UVS spectrograph and to investigate potential departures from the expec…
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Color ratios derived from molecular hydrogen emissions provide valuable diagnostics for the energy of precipitating electrons and the structure of the auroral atmosphere. We aim to characterize the horizontal and vertical variability of hydrocarbon absorption in Jupiter's auroral atmosphere using ultraviolet data from the Juno-UVS spectrograph and to investigate potential departures from the expected structure. We constructed color ratio maps sensitive to CH$_4$ and C$_2$H$_2$ absorptions for perijoves (PJs) 6 and 10, two of Juno's close approaches to Jupiter, by integrating auroral H$_2$ emission over hydrocarbon-sensitive spectral intervals. For CH$_4$, we redefined the absorbed spectral band, replacing the traditionally used 125-130 nm interval with 135-140 nm, in order to mitigate higher-order calibration issues. In regions of intense auroral brightness, we developed a correction method to account for spectral distortion due to detector non-linearities at high fluxes. CH$_4$ and C$_2$H$_2$ absorptions generally follow the expected vertical distribution, with the CH$_4$ density extending to higher altitudes than C$_2$H$_2$. However, several localized regions show unexpected spatial distribution of the absorption. In PJ6, such anomalies are attributed to instrumental non-linearities. After correction, the CR distributions become consistent with standard hydrocarbon vertical distributions. In PJ10, however, some anomalous patterns persist despite correction. Spectral modeling indicates that these can be explained by modifying the relative abundances of CH$_4$ and C$_2$H$_2$, suggesting horizontal compositional variability and possible deviations in homopause altitude between species. These findings underscore the importance of accounting for local atmospheric composition when interpreting ultraviolet auroral spectra and retrieving electron energy distributions.
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Submitted 19 August, 2025;
originally announced August 2025.
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The Pedersen and Hall Conductances in the Jovian Polar Regions: New Maps based on a Broadband Electron Energy Distribution
Authors:
G. Sicorello,
D. Grodent,
B. Bonfond,
J. -C. Gérard,
B. Benmahi,
A. Salveter,
A. Moirano,
L. A. Head,
J. Vinesse,
T. Greathouse,
G. R. Gladstone,
M. Barthélémy
Abstract:
The ionospheric Pedersen and Hall conductances play an important role in understanding the exchanges of angular momentum, energy and matter between the magnetosphere and the ionosphere/thermosphere at Jupiter, modifying the composition and temperature of the planet. In the high latitude regions, these conductances are enhanced by the auroral electron precipitation. The effect of a broadband precip…
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The ionospheric Pedersen and Hall conductances play an important role in understanding the exchanges of angular momentum, energy and matter between the magnetosphere and the ionosphere/thermosphere at Jupiter, modifying the composition and temperature of the planet. In the high latitude regions, these conductances are enhanced by the auroral electron precipitation. The effect of a broadband precipitating electron energy distribution, similar to the observed electron distributions through particle measurements, on the conductance values is investigated. The new values are compared to the ones obtained from previous studies, notably when considering a mono-energetic distribution. The broadband precipitating electron energy distribution is modeled by a kappa distribution, which is used as an input in an electron transport model that computes the density vertical profiles of ionospheric ions. The vertical profiles of the Pedersen and Hall conductivities are then evaluated assuming that the conductivities are mostly governed by the densities of H3+ and CH5+. Finally, the Pedersen and Hall conductances are computed by integrating the corresponding conductivities over altitude. The Pedersen and Hall conductances are globally higher when considering a broadband electron energy distribution rather than a mono-energetic distribution. In addition, the use of the direct outputs of an electron transport model rather than the analytical expression presented in Hiraki and Tao (2008) as well as a change in the electron collision cross-sections also have significant impacts on the conductance values. Comparison between our results and the ones deduced from the corotation enforcement theory suggests that either a physical mechanism limits the field-aligned currents or the auroral electrons precipitating in the atmosphere are also accelerated by processes not associated with the field-aligned currents.
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Submitted 14 July, 2025;
originally announced July 2025.
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Jupiter's ultraviolet auroral bridge: the influence of the solar wind on polar auroral morphology
Authors:
L. A. Head,
D. Grodent,
B. Bonfond,
A. Sulaiman,
A. Moirano,
G. Sicorello,
S. Elliott,
M. F. Vogt,
C. K. Louis,
N. Kruegler,
J. Vinesse,
T. K. Greathouse
Abstract:
Jupiters ultraviolet aurora frequently shows a number of arcs between the dusk-side polar region and the main emission, which are denoted as bridges. This work presents a largely automated detection and statistical analysis of bridges over 248 Hubble-Space-Telescope observations, alongside a multi-instrument study of crossings of magnetic field lines connected to bridges by the Juno spacecraft dur…
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Jupiters ultraviolet aurora frequently shows a number of arcs between the dusk-side polar region and the main emission, which are denoted as bridges. This work presents a largely automated detection and statistical analysis of bridges over 248 Hubble-Space-Telescope observations, alongside a multi-instrument study of crossings of magnetic field lines connected to bridges by the Juno spacecraft during its first 30 perijoves. Bridges are observed to arise on timescales of around 2 hours, can persist over a full Jupiter rotation, and are conjugate between hemispheres. The appearance of bridges is associated with compression of the magnetosphere, likely by the solar wind. Low-altitude bridge crossings are associated with upward-dominated, broadband electron distributions, consistent with Zone-II aurorae, as well as with plasma-wave emission observed by Juno-Waves, in agreement with existing theoretical models for the generation of polar-region aurorae. Main-emission crossings where no bridges are visible also show characteristics associated with bridges (more upward electron flux, plasma-wave emission), which is not the case for main-emission crossings with visible bridges, as though bridges remain present but spatially indistinguishable from the main emission in the former case. In all, compression of the magnetosphere may work to spatially separate the Zone-I and Zone-II regions of the main emission, in the form of Zone-II bridges.
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Submitted 30 June, 2025; v1 submitted 25 March, 2025;
originally announced April 2025.
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Vertical and temporal H3+ structure at the auroral footprint of Io
Authors:
A. Mura,
A. Moirano,
V. Hue,
C. Castagnoli,
A. Migliorini,
A. Altieri,
A. Adriani,
A. Cicchetti,
C. Plainaki,
G. Piccioni,
R. Noschese,
G. Sindoni,
R. Sordini
Abstract:
We report the first observation of the vertical and temporal structure of the H3+ emission at the auroral footprint of Io, as observed by Juno/JIRAM. The brightness vertical profile shows a maximum at 600 km above 1 bar, with no apparent difference between the Main Alfvén Wing spot emission and the tail of the footprint. This observation is more compatible with a broadband energy distribution of t…
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We report the first observation of the vertical and temporal structure of the H3+ emission at the auroral footprint of Io, as observed by Juno/JIRAM. The brightness vertical profile shows a maximum at 600 km above 1 bar, with no apparent difference between the Main Alfvén Wing spot emission and the tail of the footprint. This observation is more compatible with a broadband energy distribution of the precipitating electrons, than a monoenergetic one. The temporal profile of H3+ column density has been observed after the passage of the MAW and shows a hyperbolic decrease. A model of H3+ decay is proposed, which takes into account the second-order kinetic of dissociative recombination of H3+ ions with electrons. The model is found to be in very good agreement with Juno observation. The conversion factor from radiance to column density has been derived, as well as the half-life for H3+, which is not constant but inversely proportional to the H3+ column density. This explains the wide range of H3+ lifetimes proposed before.
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Submitted 27 October, 2024;
originally announced October 2024.
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Effect of magnetospheric conditions on the morphology of Jupiter's UV main auroral emission, as observed by Juno-UVS
Authors:
L. A. Head,
D. Grodent,
B. Bonfond,
A. Moirano,
B. Benmahi,
G. Sicorello,
J-C Gérard,
M. F. Vogt,
V. Hue,
T. Greathouse,
G. R. Gladstone,
Z. Yao
Abstract:
Auroral emissions are a reflection of magnetospheric processes, and, at Jupiter, it is not entirely certain how the morphology of the UV main emission (ME) varies with magnetospheric compression or the strength of the central current sheet. This work leverages the observations from Juno-UVS to link ME variability with magnetospheric states. Novel arc-detection techniques are used to determine new…
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Auroral emissions are a reflection of magnetospheric processes, and, at Jupiter, it is not entirely certain how the morphology of the UV main emission (ME) varies with magnetospheric compression or the strength of the central current sheet. This work leverages the observations from Juno-UVS to link ME variability with magnetospheric states. Novel arc-detection techniques are used to determine new reference ovals for the ME from perijoves 1 through 54, in both hemispheres, and analyse how the size and shape of the ME vary compared to this reference oval. The morphology and brightness of the ME vary in local time: the dawn-side ME is typically expanded and the dusk-side ME typically contracted compared to the reference oval, and the dusk-side ME being typically twice as bright as the dawn-side ME. Both the northern and southern ME, and the day-side and night-side ME, expand and contract from their reference ovals synchronously, which indicates that the variable size of the ME is caused by a process occurring throughout the jovian magnetosphere. The poleward latitudinal shift of the auroral footprint of Ganymede correlates with the poleward motion of the ME, whereas a similar relation is not present for the footprint of Io. Additionally, the expansion of the ME correlates well with an increase in magnetodisc current. These two results suggest that a changing current-sheet magnetic field is partially responsible for the variable size of the ME. Finally, magnetospheric compression is linked to a global ME contraction and brightening, though this brightening occurs predominantly in the day-side ME. This observation, and the observation that the dusk-side ME is typically brighter than the dawn-side ME, stands in contrast to the modelled and observed behaviour of field-aligned currents and thus weakens the theoretical link between field-aligned currents and the generation of the auroral ME.
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Submitted 8 April, 2024; v1 submitted 5 April, 2024;
originally announced April 2024.
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The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles
Authors:
Vincent Hue,
Randy Gladstone,
Corentin K. Louis,
Thomas K. Greathouse,
Bertrand Bonfond,
Jamey R. Szalay,
Alessandro Moirano,
Rohini S. Giles,
Joshua A. Kammer,
Masafumi Imai,
Alessandro Mura,
Maarten H. Versteeg,
George Clark,
Jean-Claude Gérard,
Denis C. Grodent,
Jonas Rabia,
Ali H. Sulaiman,
Scott J. Bolton,
John E. P. Connerney
Abstract:
Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co-rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfvén waves along the magnetic field lines. The position of the moons is therefore "Alfvénically" connected to their respective auroral footprint. The angular separation from the i…
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Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co-rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfvén waves along the magnetic field lines. The position of the moons is therefore "Alfvénically" connected to their respective auroral footprint. The angular separation from the instantaneous magnetic footprint can be estimated by the so-called lead angle. That lead angle varies periodically as a function of orbital longitude, since the time for the Alfvén waves to reach the Jovian ionosphere varies accordingly. Using spectral images of the Main Alfvén Wing auroral spots collected by Juno-UVS during the first forty-three orbits, this work provides the first empirical model of the Io, Europa and Ganymede equatorial lead angles for the northern and southern hemispheres. Alfvén travel times between the three innermost Galilean moons to Jupiter's northern and southern hemispheres are estimated from the lead angle measurements. We also demonstrate the accuracy of the mapping from the Juno magnetic field reference model (JRM33) at the completion of the prime mission for M-shells extending to at least 15RJ . Finally, we shows how the added knowledge of the lead angle can improve the interpretation of the moon-induced decametric emissions.
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Submitted 28 April, 2023;
originally announced April 2023.