Publications of Denis Grodent
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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 ▲]

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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 ▲]

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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 ▲]

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See detailAre Dawn Storms Jupiter's auroral Substorms?
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Gladstone, R. G. et al

Poster (2019, June)

There are multiple evidences that mass and energy rarely circulate smoothly in planetary magnetospheres. To the contrary, these systems tend to accumulate them until they fall out of balance through ... [more ▼]

There are multiple evidences that mass and energy rarely circulate smoothly in planetary magnetospheres. To the contrary, these systems tend to accumulate them until they fall out of balance through reconfiguration events. The source of mass and the source of energy can differ, as well as the trigger that initiates the collapse. However, despite some fundamental differences between the planets, the auroral signatures of the global reconfigurations bear many similarities that inform us on the common physical processes at play. For the first time, Juno has granted us a complete and global picture of one type of such reconfigurations, the auroral dawn storms, from their initiation to their vanishing. Juno actually captured views of dawn storms at different stages of development in approximately half of the cases. For example, on PJ11 and PJ16, Juno-UVS caught the brief appearence of small elongated spots located poleward of the main emission in the midnight sector. In both cases, a few hours later, the main emission began to brighten and broaden in the same sector. Then the main arc split into two parts, one moving towards the pole and the other moving equatorward. The whole feature also started to rotate towards the dawn sector, progressively accelerating to co-rotation. On PJ6, Juno-UVS observations missed the beginning of the event, but they allowed us to examine the next phase. After the broadening and the splitting of the main emission, the outer arc transformed unto large blobs. During the same time interval, subsequent Hubble Space Telescope images confirmed that the blobs kept on evolving, forming latitudinally extended fingers. All these auroral features resemble auroral morphologies observed at Earth during substorms. The Jovian elongated spots look like terrestrial poleward boundary intensifications (PBIs), the poleward motion of the arc indicates a dipolarisation/current disruption and the blobs in the outer emissions suggest massive plasma injections. [less ▲]

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See detailJupiter is alive! HST observations of Jupiter's aurora during Juno orbits 18, 19 and 20.
Grodent, Denis ULiege; Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege et al

Conference (2019, June)

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the ... [more ▼]

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the different components of Jupiter's UV aurora provide information on the evolution of the overall state of the portion of the Jovian magnetosphere to which they connect. During the present medium-size HST campaign (HST GO-15638, cycle 26), precession of the line of apsides of Juno's orbit makes it possible to probe different regions of the magnetosphere, compared to Juno orbits during previous HST cycles. Solar wind dynamics and internal processes are known to have strong influence on Jupiter's aurora, but their relative contributions and the way they couple with each other are still under debate. Cycle 26 falls during the expected minimum of the 11-year solar activity cycle. Current measurements suggest that the solar activity is already exceptionally low, with very few solar events, like CMEs, reaching Jupiter. This provides an unprecedented opportunity to observe Jupiter's aurora during a period when its magnetosphere is mainly controlled by internal processes, therefore revealing Jupiter's natural "breathing." The present HST campaign is meant to observe Jupiter's bright FUV auroral emissions in time-tag imaging mode during Juno orbits 18 to 22 (Feb-Sep 2019). We focus on the 5-day periods prior to and during Junos perijove, when Juno is sampling the current sheet region within 60 RJ, which is expected to contain the plasma source responsible for most bright auroral components, but is in a location where these aurorae cannot be observed with Juno-UVS. We sample Jupiter's emissions at a frequency of ~1 HST visit per Jovian rotation, with typically 10 HST visits for each of the 5 Juno orbits. Here we present preliminary results inferred from HST observations and concurrent Juno in situ data, obtained during Juno orbits 18, 19 and 20. [less ▲]

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See detailJupiter is alive!
 HST observations of Jupiter's aurora during Juno orbits 18, 19 and 20. (Invited)
Grodent, Denis ULiege; Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege et al

Conference (2019, June)

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the ... [more ▼]

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the different components of Jupiter's UV aurora provide information on the evolution of the overall state of the portion of the Jovian magnetosphere to which they connect. During the present medium-size HST campaign (HST GO-15638, cycle 26), precession of the line of apsides of Juno's orbit makes it possible to probe different regions of the magnetosphere, compared to Juno orbits during previous HST cycles. Solar wind dynamics and internal processes are known to have strong influence on Jupiter's aurora, but their relative contributions and the way they couple with each other are still under debate. Cycle 26 falls during the expected minimum of the 11-year solar activity cycle. Current measurements suggest that the solar activity is already exceptionally low, with very few solar events, like CMEs, reaching Jupiter. This provides an unprecedented opportunity to observe Jupiter's aurora during a period when its magnetosphere is mainly controlled by internal processes, therefore revealing Jupiter's natural "breathing." The present HST campaign is meant to observe Jupiter's bright FUV auroral emissions in time-tag imaging mode during Juno orbits 18 to 22 (Feb-Sep 2019). We focus on the 5-day periods prior to and during Junos perijove, when Juno is sampling the current sheet region within 60 RJ, which is expected to contain the plasma source responsible for most bright auroral components, but is in a location where these aurorae cannot be observed with Juno-UVS. We sample Jupiter's emissions at a frequency of ~1 HST visit per Jovian rotation, with typically 10 HST visits for each of the 5 Juno orbits. Here we present preliminary results inferred from HST observations and concurrent Juno in situ data, obtained during Juno orbits 18, 19 and 20. [less ▲]

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See detailOn the relation between Jovian aurorae and the loading/unloading of the magnetic flux: simultaneous measurements from Juno, HST and Hisaki (Invited)
Yao, Zhonghua ULiege; Grodent, Denis ULiege; Kurth, W. S. et al

Conference (2019, June)

We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in-situ measurements of magnetic field, particles and radio waves from the ... [more ▼]

We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in-situ measurements of magnetic field, particles and radio waves from the Juno Spacecraft in the outer magnetosphere, from ~ 60 RJ to 80 RJ during March 17 to 22, 2017. Two cycles of accumulation and release of magnetic flux, named magnetic loading/unloading, were identified during this period, which strongly correlate with electron energization and auroral intensifications. Magnetic reconnection events are identified during both the loading and unloading periods, indicating that reconnection and unloading are independent processes. The loading/unloading processes also correlate with MeV heavy ion fluxes, implying a potential role in Jovian X-ray emissions. [less ▲]

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See detailA brightening of Jupiter’s auroral 7.8-μm CH 4 emission during a solar-wind compression
Sinclair, J. A.; Orton, G. S.; Fernandes, J. et al

in Nature Astronomy (2019)

Enhanced mid-infrared emission from CH4 and other stratospheric hydrocarbons has been observed coincident with Jupiter’s ultraviolet auroral emission 1–3 . This suggests that auroral processes and the ... [more ▼]

Enhanced mid-infrared emission from CH4 and other stratospheric hydrocarbons has been observed coincident with Jupiter’s ultraviolet auroral emission 1–3 . This suggests that auroral processes and the neutral stratosphere of Jupiter are coupled; however, the exact nature of this coupling is unknown. Here we present a time series of Subaru-COMICS images of Jupiter measured at a wavelength of 7.80 μm on 11–14 January, 4–5 February and 17–20 May 2017. These data show that both the morphology and magnitude of the auroral CH 4 emission vary on daily timescales in relation to external solar-wind conditions. The southern auroral CH 4 emission increased in brightness temperature by about 3.8 K between 15:50 ut, 11 January and 12:57 ut, 12 January, during a predicted solar-wind compression. During the same compression, the northern auroral emission exhibited a duskside brightening, which mimics the morphology observed in the ultraviolet auroral emission during periods of enhanced solar-wind pressure 4,5 . These results suggest that changes in external solar-wind conditions perturb the Jovian magnetosphere in such a way that energetic particles are accelerated into the planet’s atmosphere, deposit their energy as deep as the neutral stratosphere, and modify the thermal structure, the abundance of CH 4 or the population of energy states of CH 4 . We also find that the northern and southern auroral CH 4 emission evolved independently between the January, February and May images, as has been observed at X-ray wavelengths over shorter timescales 6 and at mid-infrared wavelengths over longer timescales 7 . © 2019, The Author(s), under exclusive licence to Springer Nature Limited. [less ▲]

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See detailNew low electron flux facility in the 0 to 3.5 MeV range for the study of induced signal in JUICE instruments: UVS and MAJIS measurements
Carapelle, Alain ULiege; Grodent, Denis ULiege; Langevin, Yves et al

in Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2019), 440

We designed and built a new test facility to investigate signal induced by electrons in the 0-3.5 MeV in the JUICE UVS and MAJIS instruments. The facility uses radioisotopes sources to produce low flux of ... [more ▼]

We designed and built a new test facility to investigate signal induced by electrons in the 0-3.5 MeV in the JUICE UVS and MAJIS instruments. The facility uses radioisotopes sources to produce low flux of electrons (< 6000 electrons/cm².s). We present the facility, its capabilities and the results of measurements on UVS and MAJIS [less ▲]

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See detailMapping the Brightness of Ganymede's UV Aurora using HST STIS Observations
Marzok, Alexander; Saur, Joachim; Roth, Lorenz et al

Conference (2019)

Ganymede is the only known moon in the solar system with an intrinsic magnetic field and two auroral ovals around its magnetic north and south poles. In this work we analyse Hubble Space Telescope (HST ... [more ▼]

Ganymede is the only known moon in the solar system with an intrinsic magnetic field and two auroral ovals around its magnetic north and south poles. In this work we analyse Hubble Space Telescope (HST) observa- tions of Ganymede at OI 1356 Å to study the struc- ture of its auroral ovals. Our aim is to combine HST observations from various epochs to generate a bright- ness map of Ganymede’s two auroral ovals. Charged particles from Jupiter’s magnetosphere can not excite the brightest emissions of 300 R only from the re- ported electron temperatures, but need to be acceler- ated due to magnetic reconnection happening between the magnetic field lines of Jupiter and Ganymede. The sub-alfvénic speed of the charged particles makes the Ganymede system different compared to the planets in the solar wind because no bow shock is formed, re- sulting in a more steady environment that is ideal to study the phenomenon. Our created map is intended to serve as a diagnostic tool helping to investigate mag- netospheric current systems and reconnection that are responsible for the emissions and structure of the aurora. [less ▲]

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See detailX-rays Studies of the Solar System
Snios, Bradford; Dunn, William R.; Lisse, Carey M. et al

in Bulletin of the American Astronomical Society (2019), 51(3), 25

X-ray observatories advance Solar System studies by probing Sun-object interactions, developing surface composition maps, probing magnetospheric dynamics, and tracking astrochemical reactions ... [more ▼]

X-ray observatories advance Solar System studies by probing Sun-object interactions, developing surface composition maps, probing magnetospheric dynamics, and tracking astrochemical reactions. Implementing modern X-ray optics in future instruments will foster a truly transformative era of Solar System science through the study of X-ray emission. [less ▲]

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See detailSolar System Ice Giants: Exoplanets in our Backyard.
Rymer, Abigail; Mandt, Kathleen; Hurley, Dana et al

in Bulletin of the American Astronomical Society (2019), 51(3), 176

Future exoplanet exploration can be enhanced by solar system exploration, here we focus on how analysis of solar system Ice Giants can provide enhanced science return to astrophysical measurements and ... [more ▼]

Future exoplanet exploration can be enhanced by solar system exploration, here we focus on how analysis of solar system Ice Giants can provide enhanced science return to astrophysical measurements and solicit inclusion of specific wording supporting the astrophysical significance of an Ice Giant flagship- class mission in the Astro2020 report. [less ▲]

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See detailIn-Situ Observations Connected to the Io Footprint Tail Aurora
Szalay, J. R.; Bonfond, Bertrand ULiege; Allegrini, F. et al

in Journal of Geophysical Research. Planets (2018), 123(ja),

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10° to 120° along ... [more ▼]

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10° to 120° along the footprint tail. Juno's suite of magnetospheric instruments acquired detailed measurements of the Io footprint tail. Juno observed planetward electron energy fluxes of 70 mW/m2 near the Io footprint, and 10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Observed waves were primarily below the proton cyclotron frequency, yet identification of a definitive wave mode is elusive. Beyond 40° down the footprint tail, Juno observed depleted upward loss cones, suggesting the broadband acceleration occurred at distances beyond Juno's transit distance of 1.3 to 1.7 RJ. For all transits, Juno observed fine structure on scales of 10s km, and confirmed independently with electron and waves measurements that a bifurcated tail can intermittently exist. [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 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 detailCo-Rotating Magnetic Reconnection Site in Saturn's Magnetosphere
Yao, Zhonghua ULiege; Coates, A.; Ray, Licia C. 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 detailHubble Space Telescope Observations of Variations in Ganymede's Oxygen Atmosphere and Aurora
Molyneux, P. M.; Nichols, J. D.; Bannister, N. P. et al

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

We present high‐sensitivity Hubble Space Telescope (HST) Cosmic Origins Spectrograph and HST Space Telescope Imaging Spectrograph measurements of atmospheric OI 130.4‐nm and OI] 135.6‐nm emissions at ... [more ▼]

We present high‐sensitivity Hubble Space Telescope (HST) Cosmic Origins Spectrograph and HST Space Telescope Imaging Spectrograph measurements of atmospheric OI 130.4‐nm and OI] 135.6‐nm emissions at Ganymede, which exhibit significant spatial and temporal variability. These observations represent the first observations of Ganymede using HST Cosmic Origins Spectrograph and of both the leading and trailing hemispheres within a single HST campaign, minimizing the potential influence of long‐term changes in the Jovian plasma sheet or in Ganymede's atmosphere on the comparison of the two hemispheres. The mean disk‐averaged OI] 135.6‐nm/OI 130.4‐nm observed intensity ratio was 2.72 ± 0.57 on the leading hemisphere and 1.42 ± 0.16 on the trailing hemisphere. The observed leading hemisphere ratios are consistent with an O2 atmosphere, but we show that an atomic oxygen component of ~10% is required to produce the observed trailing hemisphere ratios. The excess 130.4‐nm emission on the trailing hemisphere relative to that expected for an O2 atmosphere was ~11 R. The O column density required to produce this excess is determined based on previous estimates of the electron density and temperature at Ganymede and exceeds the limit for an optically thin atmosphere. The implication that the O atmosphere is optically thick may be investigated in future by observing Ganymede as it moves into eclipse or by determining the ratio of the individual components within the 130.4‐nm triplet. [less ▲]

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See detailHST imaging of the Galilean moons Io and Ganymede and simultaneous Juno-UVS observations of the Io footprint
Roth, L.; Hue, V.; Grodent, Denis ULiege et al

in EGU General Assembly Conference Abstracts (2018, April)

The tenuous atmospheres of Jupiter's Galilean moons are key to understanding their interaction with the magnetosphere. The co-rotating magnetospheric plasma is locally perturbed at the moons and auroral ... [more ▼]

The tenuous atmospheres of Jupiter's Galilean moons are key to understanding their interaction with the magnetosphere. The co-rotating magnetospheric plasma is locally perturbed at the moons and auroral emissions are generated in the moons' tenuous atmospheres. The perturbation generates Alfvén waves, which travel along Jupiter's field lines triggering various effects that finally lead to the auroral moon footprints far away in Jupiter's polar regions. Within the large Hubble Space Telescope (HST) aurora program in support of the NASA Juno mission (HST GO-14634, PI D. Grodent), spectral images of the moons Io and Ganymede were obtained by HST's Space Telescope Imaging Spectrograph (STIS) on four occasions in 2017. In three cases, the Juno Ultraviolet Spectrograph (UVS) simultaneously observed Jupiter's polar aurora, aiming to measure the moon footprints. In this presentation, we compare the temporal variability of the local moon aurora and the footprint brightness for the case of Io. We investigate how the amplitude and phase of the periodically changing brightness of Io's aurora and the footprint are correlated. Additionally, we present the first spectral UV images of Ganymede transiting Jupiter. The Ganymede transit images are analyzed in the search for extinction by the moon's tenuous atmosphere and extended neutral cloud. [less ▲]

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See detailJuno Ultraviolet Spectrograph Observations of Jupiter's Aurora
Hue, V.; Gladstone, G. R.; Greathouse, T. K. et al

in EGU General Assembly Conference Abstracts (2018, April)

Juno is currently on an elliptical polar orbit around Jupiter, since July 2016, and has successfully gathered data during 10 perijoves sequences. Juno offers a fantastic opportunity to study Jupiter's ... [more ▼]

Juno is currently on an elliptical polar orbit around Jupiter, since July 2016, and has successfully gathered data during 10 perijoves sequences. Juno offers a fantastic opportunity to study Jupiter's magnetosphere and its spectacular auroras, which can be seen as a window screen of the entire Jovian magnetosphere. Juno not only allows for the first time to perform in-situ measurements of the particles while looking at their corresponding auroral emissions, it also gives access to unprecedented observing geometries for these emissions. The Juno Ultraviolet Spectrograph (UVS) is a UV spectrograph with a bandpass that spans 70 to 205 nm and is designed to characterize Jupiter's UV emissions. In this talk, we present an overview of Juno-UVS operations and summarize the main findings obtained after 11 perijoves. We present UV images and color ratio maps of both the northern and southern auroras of Jupiter and present a comparison with simultaneous UV-observations from the ongoing Hubble campaign supporting Juno. We discuss how the observed features evolve over a wide range of timescales utilizing data from the first perijove (PJ1, August, 27th 2016) up until PJ11 (February, 7th 2017). [less ▲]

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See detailJuno/JIRAM observation of Io and Ganymede's auroral footprints and associated tails
Mura, A.; Adriani, A.; Bolton, S. et al

in EGU General Assembly Conference Abstracts (2018, April)

JIRAM (Jovian Infrared Auroral Mapper) is an imaging spectrometer on board the NASA/Juno spacecraft. The throughput of one of the imager channels (L band) is designed to observe the auroral emission due ... [more ▼]

JIRAM (Jovian Infrared Auroral Mapper) is an imaging spectrometer on board the NASA/Juno spacecraft. The throughput of one of the imager channels (L band) is designed to observe the auroral emission due to the H3+ ion; the surface resolution, when Juno is close to Jupiter's poles, is as small as 10 km. Combined with the unique vantage point provided by Juno, JIRAM observed the auroral footprints with unprecedented details. These auroral footprints are made of bright spots (and an associated tail) that appear in Jupiter's ionosphere at the foot of the magnetic field lines that swept past Io, Europa, and Ganymede. The moons are slow-moving obstacles in the path of Jupiter's rapidly rotating magnetospheric plasma and the resulting electromagnetic interaction launches Alfven waves along the magnetic field lines towards Jupiter, where an intense electron bombardment of the hydrogen atmosphere causes it to glow. Recent observations reveal for the first time that the footprint of Io consists 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. The small scale of these multiple features ( 100 km) is incompatible with the simple paradigm of multiple Alfven wave reflections, which indeed explain the large scale multiplicity already observed. Observations of Io's trailing tail well downstream of the leading feature reveal a pair of closely spaced parallel arcs that were previously unresolved by Earth orbit observations. Both of Ganymede's footprint components (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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