References of "Radioti, Aikaterini"
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See detailTowards a global unified model of Europa's tenuous atmosphere
Plainaki; Cassidy; Shematovich et al

in Space science reviews (in press)

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See detailOverview of HST observa7ons of Jupiter’s ultraviolet aurora during Juno orbits 3 to 7
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege et al

Conference (2017, December 12)

Jupiter’s permanent ultraviolet auroral emissions have been systematically monitored from Earth orbit with the Hubble Space Telescope (HST) during an 8-month period. The Girst part of this HST large ... [more ▼]

Jupiter’s permanent ultraviolet auroral emissions have been systematically monitored from Earth orbit with the Hubble Space Telescope (HST) during an 8-month period. The Girst part of this HST large program (GO-14634) was meant to support the NASA Juno prime mission during orbits PJ03 through PJ07. The HST program will resume in Feb 2018, in time for Juno’s PJ11 perijove, right after HST’s solar and lunar avoidance periods. HST observations are designed to provide a Jovian auroral activity background for all instruments on-board Juno and for the numerous ground based and space based observatories participating to the Juno mission. In particular, several HST visits were programmed in order to obtain as many simultaneous observations with Juno-UVS as possible, sometimes in the same hemisphere, sometimes in the opposite one. In addition, the timing of some HST visits was set to take advantage of Juno’s multiple crossings of the current sheet and of the magnetic Gield lines threading the auroral emissions. These observations are obtained with the Space Telescope Imaging Spectrograph (STIS) in time-tag mode, they consist in spatially resolved movies of Jupiter’s highly dynamic aurora with timescales ranging from seconds to several days. Here, we present an overview of the present -numerous- HST results. They demonstrate that while Jupiter is always showing the same basic auroral components, it is also displaying an ever-changing auroral landscape. The complexity of the auroral morphology is such that no two observations are alike. Still, in this apparent chaos some patterns emerge. This information is giving clues on magnetospheric processes at play at the local and global scales, the latter being only accessible to remote sensing instruments such as HST. [less ▲]

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See detailCassini UVIS Observations of Saturn during the Grand Finale Orbits (Invited)
Pryor, Wayne R; Esposito, Larry W; West, Robert et al

Conference (2017, December 11)

In 2016 and 2017, the Cassini Saturn orbiter executed a final series of high inclination, low-periapsis orbits ideal for studies of 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 studies of Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) obtained an extensive set of auroral images, 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 auroral images. We will present selected images from this set showing narrow arcs of emission, more diffuse auroral emissions, multiple auroral arcs in a single image, discrete spots of emission, small scale vortices, large-scale spiral forms, and parallel linear features that appear to cross in places like twisted wires. Some shorter features are transverse to the main auroral arcs, like barbs on a wire. UVIS observations were in some cases simultaneous with auroral observations from the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) that will also be presented. UVIS polar images also contain spectral information suitable for studies of the auroral electron energy distribution. The long wavelength part of the UVIS polar images contains a signal from reflected sunlight containing absorption signatures of acetylene and other Saturn hydrocarbons. The hydrocarbon spatial distribution will also be examined. [less ▲]

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See detailCassini UVIS Auroral Observations in 2016 and 2017
Pryor, Wayne R.; Esposito, Larry W.; Jouchoux, Alain et al

Poster (2017, December 06)

In 2016 and 2017, the Cassini Saturn orbiter executed a final series of high-inclination, low-periapsis orbits ideal for studies of 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 studies of Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) obtained an extensive set of auroral images, 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 auroral images. We will present selected images from this set showing narrow arcs of emission, more diffuse auroral emissions, multiple auroral arcs in a single image, discrete spots of emission, small scale vortices, large-scale spiral forms, and parallel linear features that appear to cross in places like twisted wires. Some shorter features are transverse to the main auroral arcs, like barbs on a wire. UVIS observations were in some cases simultaneous with auroral observations from the Cassini Imaging Science Subsystem (ISS) the Cassini Visual and Infrared Mapping Spectrometer (VIMS), and the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) that will also be presented. [less ▲]

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See detailDawn Auroral Breakup at Saturn Initiated by Auroral Arcs: UVIS/Cassini Beginning of Grand Finale Phase
Radioti, Aikaterini ULiege; Grodent, Denis ULiege; Yao, Zhonghua ULiege et al

in Journal of Geophysical Research. Space Physics (2017)

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See detailJovian aurora from Juno perijove passes: comparison of ultraviolet and infrared images
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Adriani, A. et al

Conference (2017, September 01)

The electromagnetic radiation emitted by the Jovian aurora extends from the X-Rays presumably caused by heavy ion precipitation and electron bremsstrahlung to thermal infrared radiation resulting from ... [more ▼]

The electromagnetic radiation emitted by the Jovian aurora extends from the X-Rays presumably caused by heavy ion precipitation and electron bremsstrahlung to thermal infrared radiation resulting from enhanced heating by high-energy charged particles. Many observations have been made since the 1990s with the Hubble Space Telescope, which was able to image the H2 Lyman and Werner bands that are directly excited by collisions of auroral electrons with H2. Ground-based telescopes obtained spectra and images of the thermal H3+ emission produced by charge transfer between H2+ and H+ ions and neutral H2 molecules in the lower thermosphere. However, so far the geometry of the observations limited the coverage from Earth orbit and only one case of simultaneous UV and infrared emissions has been described in the literature. The Juno mission provides the unique advantage to observe both Jovian hemispheres simultaneously in the two wavelength regions simultaneously and offers a more global coverage with unprecedented spatial resolution. This was the case. [less ▲]

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See detailEvolution of the auroral signatures of Jupiter’s magnetospheric injections
Dumont, Maïté ULiege; Grodent, Denis ULiege; Bonfond, Bertrand ULiege et al

Conference (2017, September)

We report on the longitudinal and azimuthal motions of auroral signatures of Jupiter’s magnetospheric injections appearing in Hubble Space Telescope (HST) images in the northern and southern hemispheres ... [more ▼]

We report on the longitudinal and azimuthal motions of auroral signatures of Jupiter’s magnetospheric injections appearing in Hubble Space Telescope (HST) images in the northern and southern hemispheres. Based on HST spectral observations of time-tag mode and numerical simulations, we estimate the age of auroral signatures of plasma injections. [less ▲]

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See detailThe tails of the satellite auroral footprints at Jupiter
Bonfond, Bertrand ULiege; Saur, J.; Grodent, Denis ULiege et al

in Journal of Geophysical Research. Space Physics (2017), 122

The electro-magnetic interaction between Io, Europa and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint ... [more ▼]

The electro-magnetic interaction between Io, Europa and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint, takes the form of a series of spots located slightly downstream of the feet of the field lines passing through the moon under consideration. In the case of Io, these spots are also followed by an extended tail in the downstream direction relative to the plasma flow encountering the moon. A few examples of a tail for the Europa footprint have also been reported in the northern hemisphere. Here we present a simplified Alfvénic model for footprint tails and simulations of vertical brightness profiles for various electron distribution, which favour such a model over quasi-static models. We also report here additional cases of Europa footprint tails, in both hemispheres, even though such detections are rare and difficult. Furthermore, we show that the Ganymede footprint can also be followed by a similar tail. Finally, we present a case of a 320° long Io footprint tail, while other cases in similar configurations do not display such a length. [less ▲]

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See detailSimilarity of the Jovian satellite footprints: spots multiplicity and dynamics
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Badman, S. V. et al

in Icarus (2017), 292(2017), 208217

In the magnetospheres of Jupiter and Saturn, the intense interaction of the satellites Io, Europa, Ganymede and Enceladus with their surrounding plasma environment leaves a signature in the aurora of the ... [more ▼]

In the magnetospheres of Jupiter and Saturn, the intense interaction of the satellites Io, Europa, Ganymede and Enceladus with their surrounding plasma environment leaves a signature in the aurora of the planet. Called satellite footprints, these auroral features appear either as a single spot (Europa and Enceladus) or as multiple spots (Io and Ganymede). Moreover, they can be followed by extended trailing tails in the case of Io and Europa, while no tail has been reported for Ganymede and Enceladus, yet. Here we show that all Jovian footprints can be made of several spots. Furthermore, the footprints all experience brightness variations on timescale of 2-3 minutes. We also demonstrate that the satellite location relative to the plasma sheet is not the only driver for the footprint brightness, but that the plasma environment and the magnetic field strength also play a role. These new findings demonstrate that the Europa and Ganymede footprints are very similar to the Io footprint. As a consequence, the processes expected to take place at Io, such as the bi-directional electron acceleration by Alfvén waves or the partial reflection of these waves on plasma density gradients, can most likely be extended to the other footprints, suggesting that they are indeed universal processes. [less ▲]

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See detailSolar wind interaction, structure, and dynamics of the outer planet magnetospheres: A report on the ongoing activities of two ISSI teams
Vogt, Marissa; Jackman, Caitriona; Masters, Adam et al

Poster (2017, June 15)

In 2015 two teams of scientists were selected by the International Space Science Institute (ISSI) in Bern with similar goals of understanding the nature of the solar wind interaction with the ... [more ▼]

In 2015 two teams of scientists were selected by the International Space Science Institute (ISSI) in Bern with similar goals of understanding the nature of the solar wind interaction with the magnetospheres of Jupiter and Saturn and the resulting structure and dynamics of the magnetospheric boundary regions. The team “How does the Solar Wind Influence the Giant Planet Magnetospheres?” is led by Marissa Vogt and Adam Masters and the team “Structure and Dynamics of Jupiter’s Magnetosphere and Boundary Regions” is led by Caitriona Jackman and Chris Paranicas. Because these two teams share several overlapping scientific goals the teams decided to combine activities and hold a joint first meeting, which occurred in April 2016. The second team meeting will also be a joint meeting of the two teams and will be held in September 2017. Some of the outstanding research questions that the teams have been addressing include: “How do processes like magnetic reconnection and the viscous interaction at the Jovian and Saturnian magnetopauses compare to the same processes at Earth’s magnetopause?” and “Is there evidence that the solar wind drives tail reconnection at Jupiter and Saturn? If so, what process (dayside reconnection, solar wind compression) is responsible?” Here we report on some of the initial team activities, which include data analysis, modeling, and theory. Additionally, we will take this opportunity to solicit input from the wider MOP community before the second team meeting. [less ▲]

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See detailJuno, Hubble and James Webb observing Jupiter’s aurora
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege et al

Conference (2017, June 15)

Hubble Space Telescope (HST) observations of Jupiter’s aurora, supporting the Juno mission, started on 30 Nov 2016. So far, they successfully covered orbits PJ03 to PJ06. After PJ07 in July 2017, the HST ... [more ▼]

Hubble Space Telescope (HST) observations of Jupiter’s aurora, supporting the Juno mission, started on 30 Nov 2016. So far, they successfully covered orbits PJ03 to PJ06. After PJ07 in July 2017, the HST campaign will be interrupted by a solar avoidance period, preventing any observations from late August to the end of December 2017 (PJ08 to PJ10). The campaign will resume with PJ11 and continue until the end of HST cycle 25 (PJ15). Here, we present a brief summary of the HST data that has been acquired so far. It shows a broad range of auroral morphologies, suggesting that the Juno mission is sampling di ff erent facets of Jupiter’s magnetospheric activity. One should keep in mind that HST will not last forever. We should be ready to switch to the James Webb Telescope and take advantage of the overlap between the HST and JWST missions to prepare a smooth transition. The numerous infrared observations of Jupiter’s aurora obtained from ground based telescopes during Juno and obviously with Juno-JIRAM demonstrate that we can expect much from the tremendous performances of the JWST NIRCam and NIRSpec instruments. [less ▲]

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See detailConcurrent ultraviolet and infrared observations of the north Jovian aurora during Juno’s first perijove
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Gladstone, G.R. et al

Conference (2017, June 15)

The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) observed the polar aurora during the perijove phase of the first Juno orbit (PJ1) on 27 August 2016. The UVS passband ... [more ▼]

The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) observed the polar aurora during the perijove phase of the first Juno orbit (PJ1) on 27 August 2016. The UVS passband includes H2 bands that are directly excited by collisions of auroral electrons with H2. The JIRAM L-band imager includes some of the brightest H3+ features between 3.3 and 3.6 μ m. The intensity if this IR emission depends on both the column density of H3+ and the temperature in the emitting region. A series of spatial scans obtained every 30 s is used to build up images of the polar regions. JIRAM’s spatial resolution was about 100 km/pixel during most of the observations reported here while UVS has a substantially lower resolution (about 250 km/pixel). Concurrent observations were obtained during about 70 min in the north. We present a set of simultaneous ultraviolet and infrared images and point out similarities and di ff erences in their morphology and brightness distribution. The time evolution in the two spectral domains will be described and interpreted in terms of energy of the auroral electrons, time history of the precipitation and lifetime of the H3+ ions. Ultraviolet color ratio maps visualize the spatial distribution of the characteristic energy of the primary auroral electrons. Other supporting information is provided by the H3+ temperatures and column density maps derived from the analysis of JIRAM spectra covering the 2-5 μm interval. [less ▲]

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See detailNorth and South: Simultaneous observations of both Jovian poles from Juno and the Hubble Space Telescope
Bonfond, Bertrand ULiege; Gladstone, George R.; Grodent, Denis ULiege et al

Poster (2017, June 15)

On its elongated orbit, Juno flies over the poles of Jupiter every 53.5 days. The few hours before and after the perijove offer unique opportunities to observe the whole polar region from close distance ... [more ▼]

On its elongated orbit, Juno flies over the poles of Jupiter every 53.5 days. The few hours before and after the perijove offer unique opportunities to observe the whole polar region from close distance. However, Juno’s instruments can only observe one hemisphere at a time. Fortunately, the Hubble Space Telescope points its 2.4 m mirror toward the opposite hemisphere during some of these time intervals, providing truly simultaneous observations of both poles. We compare observations from Juno-UVS with Far-UV imaging sequences from the Hubble’s Space Telescope Imaging Spectrograph (STIS). Juno-UVS acquires spectrally resolved images of 17 ms exposure every 30 s Juno spin in the 70-205 nm wavelength range, while STIS can acquire about 270 consecutive 10 s images per HST orbit in the 130-160 nm range, but without any spectral resolution. Despite some differences, these datasets are similar enough in terms of spectral coverage, temporal and spatial resolution to allow direct comparisons. On Jupiter, the magnetic field is highly asymmetric and displays significant localized anomalies. Furthermore, most processes leading to auroral emissions depend on the magnetic field magnitude, either in the equatorial plane, in the acceleration regions, or in the upper atmosphere. Investigating morphological and brightness discrepancies between the two hemispheres provides precious clues on the current systems flowing in the magnetosphere and on the charged particles acceleration mechanisms. [less ▲]

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See detailAdvances on the magnetospheric dynamics of Saturn revealed from UVIS/Cassini auroral observations during the Grand finale phase of the mission
Radioti, Aikaterini ULiege; Grodent, Denis ULiege; Yao, Zhonghua ULiege et al

Poster (2017, June 13)

Auroral observations are a powerful tool to study the magnetospheric processes as they provide a ‘global picture’ of the magnetosphere at once. Here we present UVIS/Cassini auroral observations during the ... [more ▼]

Auroral observations are a powerful tool to study the magnetospheric processes as they provide a ‘global picture’ of the magnetosphere at once. Here we present UVIS/Cassini auroral observations during the Grand Finale phase of the mission. As the spacecraft approaches closely Saturn’s poles it offers an unprecedented view of the dayside and nightside auroral regions. Auroral observations which have been recently analysed from the beginning of the F-ring orbits reveal dusk/midnight arcs with a large latitudinal extent, suggesting that they are related to a source region extending from the outer to middle/inner magnetosphere. Their presence is shown to initiate dawn auroral enhancements and poleward expansions which display irregular shaped structures. Following the terrestrial example, we suggest that at Saturn the dusk/midnight arcs (possible signatures of planetward propagating plasma flows) might have caused a magnetospheric reconfiguration event, which is manifested as enhancement and poleward expansion of the dawn aurora. While the aforementioned discussion provides only the results based on the early Cassini F-ring orbits, we will also present auroral observations from the upcoming orbits with conjugate in-situ measurements. In particular, we will discuss the advances on magnetospheric dynamics at Saturn through the eyes of UVIS, during the final months of the mission. [less ▲]

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See detailMorphology of the UV aurorae Jupiter during Juno’s first perijove observations
Bonfond, Bertrand ULiege; Gladstone, G. R.; Grodent, Denis ULiege et al

in Geophysical Research Letters (2017)

On 27 August 2016, the NASA Juno spacecraft performed its first close-up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno-ultraviolet ... [more ▼]

On 27 August 2016, the NASA Juno spacecraft performed its first close-up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno-ultraviolet spectrometer UV imaging spectrograph acquired at that time. Data were acquired during four sequences (three in the north, one in the south) from 5:00 UT to 13:00 UT. From these observations, we produced complete maps of the Jovian aurorae, including the nightside. The sequence shows the development of intense outer emission outside the main oval, first in a localized region (255 ∘ –295 ∘ System III longitude) and then all around the pole, followed by a large nightside protrusion of auroral emissions from the main emission into the polar region. Some localized features show signs of differential drift with energy, typical of plasma injections in the middle magnetosphere. Finally, the color-ratio map in the north shows a well-defined area in the polar region possibly linked to the polar cap. [less ▲]

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See detailHST observations of Jupiter's UV aurora during Juno's orbits PJ03, PJ04 and PJ05
Grodent, Denis ULiege; Gladstone, G Randall; Clarke, John T. et al

Poster (2017, April)

The intense ultraviolet auroral emissions of Jupiter are currently being monitored in the frame of a large Hubble Space Telescope (HST) program meant to support the NASA Juno prime mission. The present ... [more ▼]

The intense ultraviolet auroral emissions of Jupiter are currently being monitored in the frame of a large Hubble Space Telescope (HST) program meant to support the NASA Juno prime mission. The present study addresses the three first Juno orbits (PJ03, 04 and 05) during which HST obtained parallel observations. These three campaigns basically consist of a 2-week period bracketing the time of Juno’s closest approach of Jupiter (CA). At least one HST visit is scheduled every day during the week before and the week following CA. During the ∼12-hour period centered on CA and depending on observing constraints, several HST visits are programmed in order to obtain as many simultaneous observations with Juno-UVS as possible. In addition, at least one HST visit is obtained near Juno’s apojove, when UVS is continuously monitoring Jupiter’s global auroral power, without spatial resolution, for about 12 hours. We are using the Space Telescope Imaging Spectrograph (STIS) in time-tag mode in order to provide spatially resolved movies of Jupiter’s highly dynamic aurora with timescales ranging from seconds to several days. We discuss the preliminary exploitation of the HST data and present these results in such a way as to provide a global magnetospheric context for the different Juno instruments studying Jupiter’s magnetosphere, as well as for the numerous ground based and space based observatories participating to the Juno mission. [less ▲]

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See detailMulti-instrument overview of the 1-hour pulsations in Saturn's magnetosphere
Palmaerts, Benjamin ULiege; Roussos, Elias; Radioti, Aikaterini ULiege et al

Conference (2017, March 16)

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See detailAuroral streamer and its role in driving wave-like pre-onset aurora
Yao, Zhonghua ULiege; Pu, Z. Y.; Rae, I. J. et al

in Geoscience Letters (2017), 4(1), 8

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See detailSaturn's auroral arc
Radioti, Aikaterini ULiege

in Nature Astronomy (2017), 1

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