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See detailSimilarity of the Jovian satellite footprints: spots multiplicity and dynamics
Bonfond, Bertrand ULg; Grodent, Denis ULg; 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 detailNorth and South: Simultaneous observations of both Jovian poles from Juno and the Hubble Space Telescope
Bonfond, Bertrand ULg; Gladstone, George R.; Grodent, Denis ULg 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 detailMorphology of the UV aurorae Jupiter during Juno’s first perijove observations
Bonfond, Bertrand ULg; Gladstone, G. R.; Grodent, Denis ULg 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 ULg; 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 detailImplications of Juno energetic particle observations over Jupiter’s polar regions for understanding magnetosphere-ionosphere coupling at strongly magnetized planets
Mauk, Barry; Haggerty, Dennis; Paranicas, Christopher et al

Conference (2017, April)

Juno obtained low altitude space environment measurements over Jupiter’s poles on 27 August 2016 and then again on 11 December 2016. Particle distributions were observed over the poles within the downward ... [more ▼]

Juno obtained low altitude space environment measurements over Jupiter’s poles on 27 August 2016 and then again on 11 December 2016. Particle distributions were observed over the poles within the downward loss cones sufficient to power nominally observed auroral emissions and with the characteristic energies anticipated from remote spectroscopic ultra-violet auroral imaging. However, the character of the particle distributions apparently causing the most intense auroral emissions were very different from those that cause the most intense aurora at Earth and from those anticipated from prevailing models of magnetosphere-ionosphere coupling at Jupiter. The observations are highly suggestive of a predominance of a magnetic field-aligned stochastic acceleration of energetic auroral electrons rather than the more coherent acceleration processes anticipated. The Juno observations have similarities to observations observed at higher altitudes at Saturn by the Cassini mission suggesting that there may be some commonality between the magnetosphere-ionosphere couplings at these two giant planets. Here we present the Juno energetic particle observations, discuss their similarities and differences with published observations from Earth and Saturn, and deliberate on the implications of these finding for general understanding of magnetosphere-ionosphere coupling processes. [less ▲]

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See detailSynergistic observations of the giant planets with HST and JWST: Jupiter's auroral emissions
Grodent, Denis ULg

Conference (2017, March 20)

The James Webb Space Telescope is perfectly suited to observe most Solar System objects, including the extended giant planets. Its high sensitivity, high spatial resolution, field of view, very high ... [more ▼]

The James Webb Space Telescope is perfectly suited to observe most Solar System objects, including the extended giant planets. Its high sensitivity, high spatial resolution, field of view, very high spectral resolution and wide spectral coverage all combine to make JWST a fantastic instrument that will result in significant advances and progress in most fields of Solar System exploration. Here, we focus on the case of Jupiter’s aurora for several reasons. 1) The auroral emissions on Jupiter are very intense, both in ultraviolet and in infrared. Each of these bandpasses is bringing complementary information on how Jupiter is interacting with its near and distant environment. 2) Even though Jupiter’s aurora appears to be responding to the conditions prevailing in the solar wind, contrary to the Earth it is a permanent emission that can also be observed on the sunlit side of the planet. 3) The NASA Juno mission is currently exploring the magnetosphere and the atmosphere of this planet with a suite of in situ and remote instruments, including an ultraviolet spectrograph (UVS) and an infrared imaging spectrograph (JIRAM). The Juno mission is gathering a broad scientific community that will foster the study of Jupiter’s system for several years. 4) A large HST program was allocated in support of the NASA Juno prime mission (GO-14634) and is currently providing us with regular movies of Jupiter’s ultraviolet aurora. They provide a global magnetospheric context for the different Juno instruments, as well as for the numerous ground based (infrared) and space based observatories participating to the Juno mission. 5) It is currently very difficult to plan truly simultaneous UV and IR observations, mainly because of the inherent limitations of Earth based infrared telescopes. As a result, comparisons of Jupiter’s auroral emissions rest on a very limited dataset. Nevertheless, they are suggesting similarities and discrepancies between IR and UV aurorae, the study of which would greatly benefit from synergistic observations with HST and JWST. 6) The case of Saturn’s aurora is as important, especially in view of the upcoming ‘Grand Finale’ of the Cassini mission, and all above arguments apply to Saturn as well. The case of Uranus and Neptune’s aurorae still belongs to the area of discovery and will take full advantage of JWST’s advanced capabilities. [less ▲]

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

Conference (2017, March 16)

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See detailStagnation of Saturn's auroral emission at noon
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2017)

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See detailJupiter's magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits
Connerney, J. E. P.; Adriani, A.; Allegrini, F. et al

in Science (2017), 356(6340), 826--832

Jupiter is the largest and most massive planet in our solar system. NASA\textquoterights Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al ... [more ▼]

Jupiter is the largest and most massive planet in our solar system. NASA\textquoterights Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno\textquoterights flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter\textquoterights aurorae and plasma environment, both as Juno approached the planet and during its first close orbit.Science, this issue p. 821, p. 826The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno\textquoterights capture orbit spanned the jovian magnetosphere from bow shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno\textquoterights passage over the poles and traverse of Jupiter\textquoterights hazardous inner radiation belts. Juno\textquoterights energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator. [less ▲]

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See detailResponse of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno
Nichols, J. D.; Badman, S. V.; Bagenal, F. et al

in Geophysical Research Letters (2017)

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the ... [more ▼]

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought. [less ▲]

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See detailJuno-UVS Approach Observations of Jupiter's Auroras
Gladstone, G. R.; Versteeg, M. H.; Greathouse, T. K. et al

in Geophysical Research Letters (2017)

Juno-UVS observations of Jupiter's aurora obtained during approach are presented. Prior to the bow-shock crossing on 24 June 2016, the Juno approach provided a rare opportunity to correlate local solar ... [more ▼]

Juno-UVS observations of Jupiter's aurora obtained during approach are presented. Prior to the bow-shock crossing on 24 June 2016, the Juno approach provided a rare opportunity to correlate local solar wind conditions with Jovian auroral emissions. Some of Jupiter's auroral emissions are expected to be controlled or modified by local solar wind conditions. Here we compare synoptic Juno-UVS observations of Jupiter's auroral emissions, acquired during 3-29 June 2016, with in situ solar wind observations, and related Jupiter observations from Earth. Four large auroral brightening events are evident in the synoptic data, in which the total emitted auroral power increases by a factor of 3-4 for a few hours. Only one of these brightening events correlates well with large transient increases in solar wind ram pressure. The brightening events which are not associated with the solar wind generally have a rise time of ~2 hours and a decay time of ~5 hours. [less ▲]

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See detailEnergy Dissipation in Saturn’s Magnetotail: A Comparative Magnetotail Approach
Yao, Zhonghua ULg; Coates, Andrew; Ray, Licia et al

Poster (2016, December 16)

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See detailThe complex behavior of the satellite footprints at Jupiter: the result of universal processes?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah V. et al

Poster (2016, December 14)

At Jupiter, some auroral emissions are directly related to the electromagnetic interaction between the moons Io, Europa and Ganymede on one hand and the rapidly rotating magnetospheric plasma on the other ... [more ▼]

At Jupiter, some auroral emissions are directly related to the electromagnetic interaction between the moons Io, Europa and Ganymede on one hand and the rapidly rotating magnetospheric plasma on the other hand. Out of the three, the Io footprint is the brightest and the most studied. Present in each hemisphere, it is made of at least three different spots and an extended trailing tail. The variability of the brightness of the spots as well as their relative location has been tentatively explained with a combination of Alfvén waves’ partial reflections on density gradients and bi-directional electron acceleration at high latitude. Should this scenario be correct, then the other footprints should also show the same behavior. Here we show that all footprints are, at least occasionally, made of several spots and they all display a tail. We also show that these spots share many characteristics with those of the Io footprint (i.e. some significant variability on timescales of 2-3 minutes). Additionally, we present some Monte-Carlo simulations indicating that the tails are also due to Alfvén waves electron acceleration rather than quasi-static electron acceleration. Even if some details still need clarification, these observations strengthen the scenario proposed for the Io footprint and thus indicate that these processes are universal. In addition, we will present some early results from Juno-UVS concerning the location and morphology of the footprints during the first low-altitude observations of the polar aurorae. These observations, carried out in previously unexplored longitude ranges, should either confirm or contradict our understanding of the footprints. [less ▲]

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See detailJupiter’s auroras during the Juno approach phase as observed by the Hubble Space Telescope
Nichols, Jonathan D; Clarke, John T; Orton, Glennn S et al

Conference (2016, December 13)

We present movies of the Hubble Space Telescope (HST) observations of Jupiter’s FUV auroras observed during the Juno approach phase and first capture orbit, and compare with Juno observations of the ... [more ▼]

We present movies of the Hubble Space Telescope (HST) observations of Jupiter’s FUV auroras observed during the Juno approach phase and first capture orbit, and compare with Juno observations of the interplanetary medium near Jupiter and inside the magnetosphere. Jupiter’s FUV auroras indicate the nature of the dynamic processes occurring in Jupiter’s magnetosphere, and the approach phase provided a unique opportunity to obtain a full set of interplanetary data near to Jupiter at the time of a program of HST observations, along with the first simultaneous with Juno observations inside the magnetosphere. The overall goal was to determine the nature of the solar wind effect on Jupiter’s magnetosphere. HST observations were obtained with typically 1 orbit per day over three intervals: 16 May – 7 June, 22-30 June and 11-18 July, i.e. while Juno was in the solar wind, around the bow shock and magnetosphere crossings, and in the mid-latitude middle-outer magnetospheres. We show that these intervals are characterised by particularly dynamic polar auroras, and significant variations in the auroral power output caused by e.g. dawn storms, intense main emission and poleward forms. We compare the variation of these features with Juno observations of interplanetary compression regions and the magnetospheric environment during the intervals of these observations. [less ▲]

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See detailInitial observations of Jupiter’s aurora from Juno’s Ultraviolet Spectrograph (Juno-UVS)
Gladstone, Randy; Versteeg; Greathouse, Thomas et al

Conference (2016, December 13)

Juno-UVS is an imaging spectrograph with a bandpass of 70<λ<205 nm. This wavelength range includes important far-ultraviolet (FUV) emissions from the H2 bands and the H Lyman series which are produced in ... [more ▼]

Juno-UVS is an imaging spectrograph with a bandpass of 70<λ<205 nm. This wavelength range includes important far-ultraviolet (FUV) emissions from the H2 bands and the H Lyman series which are produced in Jupiter’s auroras, and also the absorption signatures of aurorally-produced hydrocarbons. The Juno-UVS instrument telescope has a 4x4 cm2 input aperture and uses an off-axis parabolic primary mirror. A flat scan mirror situated near the entrance of the telescope is used to observe at up to ±30° perpendicular to the Juno spin plane. The light is focused onto the spectrograph entrance slit, which has a “dog-bone” shape, with three sections of 2.55°x0.2°, 2.0°x0.025°, and 2.55°x0.2° (as projected onto the sky). Light entering the slit is dispersed by a toroidal grating which focuses FUV light onto a curved microchannel plate (MCP) cross delay line (XDL) detector with a solar blind UV-sensitive CsI photocathode. The two mirrors and the grating are coated with MgF2 to improve FUV reflectivity. Tantalum surrounds the spectrograph assembly to shield the detector and its electronics from high-energy electrons. All other electronics are located in Juno’s spacecraft vault, including redundant low-voltage and high-voltage power supplies, command and data handling electronics, heater/actuator electronics, scan mirror electronics, and event processing electronics. The purpose of Juno-UVS is to remotely sense Jupiter’s auroral morphology and brightness to provide context for in situ measurements by Juno’s particle instruments. Here we present the first near-Jupiter results from the UVS instrument following measurements made during PJ1, Juno’s first perijove pass with its instruments powered on and taking data. [less ▲]

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See detailSearch for low-latitude atmospheric hydrocarbon variations on Jupiter from Juno-UVS measurements
Hue, Vincent; Gladstone, Randy; Greathouse, Thomas et al

Conference (2016, December 13)

The Juno mission offers the opportunity to study Jupiter, from its inner structure, up to its magnetospheric environment. Juno was launched on August 2011 and its Jupiter orbit insertion (JOI) occurred on ... [more ▼]

The Juno mission offers the opportunity to study Jupiter, from its inner structure, up to its magnetospheric environment. Juno was launched on August 2011 and its Jupiter orbit insertion (JOI) occurred on July 4th 2016. The nominal Juno mission involves 35 science polar-orbits of 14-days period, with perijove and apojove distances located at 0.06 Rj and 45 Rj, respectively. Juno-UVS is a UV spectrograph with a bandpass of 70<λ<205 nm, designed to characterize Jupiter UV emissions. One of the main additions of UVS compared to its predecessors (New Horizons- and Rosetta- Alice, LRO-LAMP) is a 2.54 mm tantalum shielding, to protect it from the harsh radiation environment at Jupiter, and a scan mirror, to allow for targeting specific auroral and atmospheric features at +/- 30˚ perpendicular to the Juno spin plane. It will provide new constraints on Jupiter’s auroral morphology, spectral features, and vertical structure, while providing remote-sensing constraints for the onboard waves and particle instruments. It will also be used to probe upper-atmospheric composition through absorption features found in the UV spectra using reflected solar UV radiation. For example, stratospheric hydrocarbons such as C2H2 and C2H6 are known to absorb significantly in the 150-180 nm regions, and these absorption features can be used to determine their abundances. We will present our search for the spectroscopic features seen in Jupiter’s reflected sunlight during the first perijove. [less ▲]

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See detailDynamics of the flares in the active polar region of Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, S. V. et al

in Geophysical Research Letters (2016)

The dusk-side of the polar region of Jupiter's UV aurorae, called the active region, sometimes exhibits quasi-periodic (QP) flares on time-scales of 2-3 minutes. Based on Hubble Space Telescope Far-UV ... [more ▼]

The dusk-side of the polar region of Jupiter's UV aurorae, called the active region, sometimes exhibits quasi-periodic (QP) flares on time-scales of 2-3 minutes. Based on Hubble Space Telescope Far-UV time-tag images, we show for the first time that the northern hemisphere also displays QP-flares. The area covered by these flares can reach up to 2.4 × 108 km2 (i.e. the whole active region), but often only involves an area an order of magnitude smaller. Using a magnetic field mapping model, we deduced that these areas correspond to the dayside outer magnetosphere. In our dataset, quasi-periodic features are only seen on half of the cases and even on a given observation, a region can be quiet for one half and blinking on the other half. Consecutive observations in the two hemispheres show that the brightening can occur in phase. Combined with the size and location of the flares, this behaviour suggests that the QP-flares most likely take place on closed magnetic field lines. [less ▲]

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See detailFirst Hubble Space Telescope Movies of Jupiter’s Ultraviolet Aurora During the NASA Juno Prime Mission
Grodent, Denis ULg; Gladstone, G. Randall; Clarke, John T. et al

Poster (2016, December)

The primary goal of this HST campaign is to complement Juno-UVS (Ultraviolet Spectrograph) observations. This complementarity is four-fold as HST observes Jupiter’s aurora when: 1) Juno-UVS is turned off ... [more ▼]

The primary goal of this HST campaign is to complement Juno-UVS (Ultraviolet Spectrograph) observations. This complementarity is four-fold as HST observes Jupiter’s aurora when: 1) Juno-UVS is turned off, that is about 98% of Juno’s 14-day orbit, and Juno’s in situ instruments are in operation. 2) Juno-UVS is operating, but observes the opposite hemisphere of Jupiter. 3) UVS is on in the same hemisphere, but too close to Jupiter to have a global, contextual, view of the aurora and/or UVS is affected by the noise induced by Jupiter’s radiation belts. 4) Juno is too far from Jupiter to get a detailed view of the aurora. In addition, HST will observe the auroral and airglow emissions of the Galilean moons Io, Ganymede and Europa, when UVS is measuring their auroral footprints in Jupiter’s ionosphere. During this campaign, HST is obtaining 45-min STIS time-tag images -movies- of both hemispheres of Jupiter and STIS/COS spectra of Jupiter's moons. These observations are taking place during 4 sequences of Juno's orbit (Figure: typical orbit in magnetic coordinates): 1) Perijove segment: a 6-hour sequence bracketing the time of Juno's closest approach of Jupiter. 2) Crossing segments: few hours periods during which Juno is crossing the magnetic equator of Jupiter and in situ instruments are observing the plasma sheet particles. 3) Perijove +/- 1 Jovian rotation (or more), to provide a context for the auroral activity before and after perijove. 4) Apojove segment: a 12-hour period bracketing the time when Juno is farthest from Jupiter and Juno-UVS is continuously monitoring the global auroral UV power of Jupiter. During Juno orbit PJ5, between 28 Nov. and 07 Dec. 2016, HST obtains 9 STIS movies: 3 movies of the northern aurora near perijove, 1 movie (north) one Jovian rotation before and 2 movies (south- north) one and two Jovian rotations after perijove, 2 movies (north) during two close CS crossings, and 1 movie near apojove. These movies will be commented during this presentation. [less ▲]

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See detailContinuous Monitoring of Jupiter's Aurora and Io Plasma Torus with the Hisaki Satellite during Joint Observing Campaign with Juno
Kimura, Tomoki; Yamazaki, Atsushi; Murakami, Go et al

Poster (2016, December)

The Hisaki satellite is the first space telescope that is dedicated to observations of our solar system bodies. Hisaki has been continuously monitoring the atmosphere and magnetosphere of the solar system ... [more ▼]

The Hisaki satellite is the first space telescope that is dedicated to observations of our solar system bodies. Hisaki has been continuously monitoring the atmosphere and magnetosphere of the solar system bodies with the extreme ultraviolet (EUV) spectroscope EXCEED since the launch in September 2013. Dynamics on timescales from 10s minutes to a few years were discovered in the atmosphere and magnetosphere by the continuous monitoring. Large joint observing campaigns for Jupiter by the Juno spacecraft in coordination with Hisaki, the Hubble Space Telescope (HST), and other facilities started in mid-2016. Before Jupiter Orbit Insertion, Juno made the in-situ solar wind measurements while Hisaki was simultaneously monitoring Jupiter's aurora and Io plasma torus. On Day of Year 142, Hisaki discovered that the EUV auroral emission power rapidly increased by a factor of ~3 but returned to a nominal level within one planetary rotation. The transient aurora was followed by brightening of the torus sulfur and oxygen ions that is proxy of the hot electron populations in the torus. At the same time, the relatively weak solar wind shock signatures were found in the JUNO/JEDI energetic particle data (Clark et al.). The transient variability is compared to the morphology observed by HST (Nichols et al.). Hisaki is going to monitor Jupiter in collaboration with the large observing program of HST (Grodent et al.) that will make ~150 exposures from this November. [less ▲]

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See detailProperties of Jupiter’s auroral acceleration region inferred with HST-STIS spectral images
Ray, Licia C.; Arridge, Christopher S.; Gustin, Jacques et al

Poster (2016, December)

Jupiter’s dynamic auroral region is the signature of magnetosphere-ionosphere coupling. Precipitating auroral electrons are part of a current system which transports angular momentum from the planetary ... [more ▼]

Jupiter’s dynamic auroral region is the signature of magnetosphere-ionosphere coupling. Precipitating auroral electrons are part of a current system which transports angular momentum from the planetary atmosphere to sub-corotating magnetospheric plasma. The magnitude of the currents and hence precipitating energy flux, are sensitive to the characteristics of the high-latitude magnetosphere, in particular the location of the auroral acceleration region (AAR) and the density and temperature of the high-latitude electron population. We use HST STIS observations of Jupiter’s aurora (Gustin et al. [2016]) to infer the location of the AAR and the properties of the precipitating auroral electrons. To do this, we determine the energy of the precipitating electrons and incident energy flux for the two distinct regions within the main aurora and within flare regions. The resulting relationships between energy flux and electron precipitation energy for the main auroral emission are then compared to the theoretical relationship derived by Lundin & Sandahl [1978], in order to derive the location of the AAR and the temperatures and densities of the electrons at the top of the AAR prior to acceleration. We find that that each emission region is best reproduced using a multiple auroral acceleration regions with different properties, rather than a single auroral acceleration region with a varying potential drop strength. [less ▲]

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