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See detailMUZUBI – Advanced phase unwrapping using split-band interferometry
Defrere, Denis ULiege; Radioti, Aikaterini ULiege; De Rauw, Dominique ULiege et al

Scientific conference (2019, November 28)

Absolute phase retrieval is a mandatory pre-requisite for accurate topographic measurements from SAR interferometric data. Because they use the phase of a starting point as a reference level, classical ... [more ▼]

Absolute phase retrieval is a mandatory pre-requisite for accurate topographic measurements from SAR interferometric data. Because they use the phase of a starting point as a reference level, classical phase unwrapping techniques usually fail to connect regions separated by non-coherent areas and require additional corrections to produce continuous phase maps which are consistent with the ground truth. A technique commonly used for that purpose is split-band interferometry, also known as multi chromatic analysis (MCA), which exploits the large range bandwidth of SAR sensors such as TerraSAR-X / TanDEM-X. The idea behind this technique is that the absolute phase is proportional to the intercept and slope of the spectrally-dispersed phase across individual sub-bands. Previous MCA analysis generally focused on the search of carefully-chosen targets, called frequency-persistent scatterers, which are used to estimate the global phase offset of the entire disconnected region. In this study, we take another approach and argue that all pixels in each independently-unwrapped region carry useful information that can be used to improve the precision on the absolute phase. In the context of the MUZUBI project, we have applied this idea to TerraSAR-X / TanDEM-X and SENTINEL images and investigated the effect of sensor bandwidth, mean coherence across the region, and region size on the precision of the computed absolute phase. [less ▲]

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See detailAuroral Beads at Saturn and the Driving Mechanism: Cassini Proximal Orbits
Radioti, Aikaterini ULiege; Yao, Zhonghua ULiege; Grodent, Denis ULiege et al

in Astrophysical Journal (2019), 885

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

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

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See detailFundamental Limit of Absolute Phase Retrieval with Split-Band Interferometry: Application to TerraSAR-X / TanDEM-X and SENTINEL Images
Defrere, Denis ULiege; Radioti, Aikaterini ULiege; Libert, Ludivine et al

Scientific conference (2019, October 24)

Accurate topographic and deformation measurements from SAR interferometry require to correctly unwrap the phase. However, classical phase unwrapping often fails at connecting different regions separated ... [more ▼]

Accurate topographic and deformation measurements from SAR interferometry require to correctly unwrap the phase. However, classical phase unwrapping often fails at connecting different regions separated by low coherence. This results in phase jumps, difficult to correct or even detect without proper ground measurements. One solution consists in using the topographic and deformation phase dependence with the wavelength. Using large bandwidth SAR acquisitions such as TerraSAR-X Spotlight images, we can apply split-band interferometry (SBInSAR) in order to produce different interferograms with slightly different center-frequencies. The absolute topographic phase is then proportional to the slope of individuals split-band interferograms. Previous MCA analysis generally focused on the search of carefully-chosen targets, called frequency-persistent scatterers (PSf). If they exist, these PSfs could be used to estimate the global phase offset of the entire disconnected region. Here, we take another approach and argue that all pixels in each independently-unwrapped region carry useful information on the absolute phase. All this information can finally be used to improve the precision on the absolute phase. In the context of the MUZUBI project, we have applied this idea to TerraSAR-X / TanDEM-X, CSK, and SENTINEL images. We investigated the effect of sensor bandwidth, mean coherence across the region, and region size on the precision of the computed absolute phase. The technique is also compared with the results of the SRTM digital elevation model. In the end, we derived the fundamental limits of applicability of split-band interferometry. [less ▲]

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See detailOn the 1-hour periodicities in the Saturnian system
Palmaerts, Benjamin ULiege; Roussos, E.; Grodent, Denis ULiege et al

Conference (2019, July 30)

The exploration of the magnetospheres of magnetized planets has revealed periodic phenomena with a large variety of periods. In Saturn's magnetosphere, oscillations with a period of about one hour are ... [more ▼]

The exploration of the magnetospheres of magnetized planets has revealed periodic phenomena with a large variety of periods. In Saturn's magnetosphere, oscillations with a period of about one hour are commonly identified in charged particle fluxes, in the magnetic field, in plasma waves and in the brightness of localized auroral structures. We will present a review of these 1-hour oscillations using multi-instrument observations acquired during the 13 years of the Cassini mission. We will discuss possible triggers in light of the Cassini observations of the 1-hour periodicities. The presence of 1-hour quasi-periodic electrons in the close vicinity of the magnetopause supports the involvement of magnetopause processes, such as magnetic reconnection and Kelvin-Helmholtz instabilities. Pulsed electrons are also encountered much deeper in the magnetosphere and may originate from reconnection in the magnetodisk, on both the day and night sides of the magnetosphere. Moreover, similar mechanisms might take place also in the magnetosphere of Jupiter, leading to the observed periodic phenomena. [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 detailOrigin and triggers of the 1-hour electron pulsations in the Saturnian system
Palmaerts, Benjamin ULiege; Burkholder, B.; Delamere, P. A. et al

Conference (2019, June 07)

Phenomena displaying a periodicity of around one hour have been frequently observed in Saturn's magnetosphere during the Cassini era. In particular, flux of energetic electrons can exhibit 1-hour quasi ... [more ▼]

Phenomena displaying a periodicity of around one hour have been frequently observed in Saturn's magnetosphere during the Cassini era. In particular, flux of energetic electrons can exhibit 1-hour quasi-periodic pulsations. While these pulsations have been well characterized, their origin and the processes triggering them remained uncertain at the end of the Cassini mission. Using long imaging sequences of the auroral emissions at Saturn, we report the first direct observational evidence that the 1-hour periodicities arise from a global 1-hour oscillation of the Kronian magnetosphere. This natural oscillation acts independently of the local magnetospheric conditions and can have multiple triggering processes. Many 1-hour quasi-periodic electrons were encountered close to the magnetopause, suggesting that magnetopause processes could trigger them, such as magnetic reconnection and Kelvin-Helmholtz (KH) instabilities. We now report simultaneous presence of KH instabilities and 1-hour electron pulsations, supporting this scenario. Pulsed electrons are also encountered much deeper in the magnetosphere and may originate from reconnection in the magnetodisk, on both the day and night sides of the magnetosphere. [less ▲]

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See detailA nearly corotating long lasting auroral spiral at Saturn
Palmaerts, Benjamin ULiege; Yao, Zhonghua ULiege; Sergis, N. et al

Poster (2019, June 04)

The main ultraviolet auroral emission at Saturn consists of multiple structures of various sizes forming a discontinuous ring of emissions around Saturn’s poles. For decades, it is known that the main ... [more ▼]

The main ultraviolet auroral emission at Saturn consists of multiple structures of various sizes forming a discontinuous ring of emissions around Saturn’s poles. For decades, it is known that the main emission is occasionally organized in a global spiral surrounding the pole. In August 2016, the Ultraviolet Imaging Spectrograph (UVIS) on board the Cassini spacecraft proceeded to a 7h-long imaging of Saturn’s northern aurora. During this observing sequence, the main emission displayed a spiral wrapping around the pole by more than 370° in longitude. The spiral was in rotation around the pole at ~90% of rigid corotation, which is an unusually high velocity for extended auroral structures. A spiral was again observed during a shorter UVIS sequence, sixteen hours after the end of the first sequence. Simultaneously to the first UVIS sequence, imaging of the energetic neutral atom (ENA) emissions revealed a hot plasma population in the same local time sector as the extremity of the UV spiral. The leading edge of the plasma population follows the spiral structure around the planet. This correspondence suggests that the presence of the hot plasma distorted the magnetospheric current system, resulting in the spiral shape of the main emission. Furthermore, simultaneous in-situ measurements of the ion fluxes exhibit enhancements recurring every ~10.5 hours. The nearly corotating aurora, ENA emissions and ions revealed by this multi-instrument dataset are likely three signatures of a magnetosphere-ionosphere coupling current system and of the associated hot plasma population corotating with the planet. [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
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 detailElectron pulsations generated by rotating magnetospheric dynamics at Saturn
Guo, Ruilong ULiege; Yao, Zhonghua ULiege; Sergis, N et al

Poster (2019, June)

Quasi-periodic pulsations of energetic electrons have been frequently observed in Saturn's magnetosphere. The mechanisms for the electron pulsations are far from conclusive, although generally believed to ... [more ▼]

Quasi-periodic pulsations of energetic electrons have been frequently observed in Saturn's magnetosphere. The mechanisms for the electron pulsations are far from conclusive, although generally believed to be associated with field-line resonance due to their similar periodicities. Here we report an electron pulsation event that is related to aurora beads and energetic neutral atom (ENA) emissions. The perturbation of the magnetic field indicates that Cassini spacecraft encountered a series of field-aligned currents (FACs) connected to the aurora beads. The fluxes of energetic electrons were enhanced when the spacecraft crossed the FACs. Both aurora beads and ENA emission were rotating. Given that the FACs interconnect the aurora beads and the active region at equator, a hot plasma population associated with the ENA enhancement, we conclude that the FACs were rotating with Saturn and had finite extent in the azimuthal direction. The periodic features also manifested in the whistler-mode auroral hiss emissions in the same event. We proposed that the electron pulsations we studied are spatial effect of the rotating magnetosphere. The rotation of the whole magnetosphere transfers the spatial effect to the temporal effect, i.e., the pulsation sequences observed by Cassinis multiple instruments. [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 detailDayside magnetodisk reconnection processes on Saturn revealed by Cassini
Guo, Ruilong ULiege; Yao, Zhonghua ULiege; Wei, Y. et al

Conference (2019, June)

Magnetic reconnection is a fundamental plasma process that energizes charged particles explosively, generating phenomena such as nebular flares, solar flares, and stunning aurorae. In planetary ... [more ▼]

Magnetic reconnection is a fundamental plasma process that energizes charged particles explosively, generating phenomena such as nebular flares, solar flares, and stunning aurorae. In planetary magnetospheres, magnetic reconnection has often been identified on the dayside magnetopause and in the nightside magnetotail and/or magnetodisk. For giant planets, the dayside magnetodisk is usually considered thicker than the nightside due to the compression of solar wind, and thus not an ideal environment for reconnection. However, in this work, we report a series of evidences of near-noon reconnection within Saturn's magnetodisk using measurements from the Cassini spacecraft. An ion diffusion region is well defined based on the analysis of the Hall magnetic field and the electron pitch angle distribution. The results suggest that the rotationally driven reconnection process plays a key role in producing energetic electrons (up to 100 keV) and ions (several hundreds of kiloelectron volts). In particular, we find that energetic oxygen ions are locally accelerated at the reconnection sites, which shed light to understanding of Jovian X-ray aurorae caused by MeV ion precipitations. [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 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 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 detailContemporaneous Observations of Jovian Energetic Auroral Electrons and Ultraviolet Emissions by the Juno Spacecraft
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Mauk, B. H. et al

in Journal of Geophysical Research: Space Physics (2019), 124(11), 8298--8317

We present comparisons of precipitating electron flux and auroral brightness measurements made during several Juno transits over Jupiter's auroral regions in both hemispheres. We extract from the ... [more ▼]

We present comparisons of precipitating electron flux and auroral brightness measurements made during several Juno transits over Jupiter's auroral regions in both hemispheres. We extract from the ultraviolet spectrograph (UVS) spectral imager H2 emission intensities at locations magnetically conjugate to the spacecraft using the JRM09 model. We use UVS images as close in time as possible to the electron measurements by the Jupiter Energetic Particle Detector Instrument (JEDI) instrument. The upward electron flux generally exceeds the downward component and shows a broadband energy distribution. Auroral intensity is related to total precipitated electron flux and compared with the energy-integrated JEDI flux inside the loss cone. The far ultraviolet color ratio along the spacecraft footprint maps variations of the mean energy of the auroral electron precipitation. A wide diversity of situations has been observed. The intensity of the diffuse emission equatorward of the main oval is generally in fair agreement with the JEDI downward energy flux. The intensity of the ME matches exceeds or remains below the value expected from the JEDI electron energy flux. The polar emission may be more than an order of magnitude brighter than associated with the JEDI electron flux in association with high values of the color ratio. We tentatively explain these observations by the location of the electron energization region relative to Juno's orbit as it transits the auroral region. Current models predict that the extent and the altitude of electron acceleration along the magnetic field lines are consistent with this assumption. [less ▲]

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See detailOn the Relation Between Jovian Aurorae and the Loading/Unloading of the Magnetic Flux: Simultaneous Measurements From Juno, Hubble Space Telescope, and Hisaki
Yao, Zhonghua ULiege; Grodent, Denis ULiege; Kurth, W. S. et al

in Geophysical Research Letters (2019)

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 ~ 80RJ to 60RJ during 17 to 22 March 2017. Two cycles of accumulation and release of magnetic flux, named magnetic loading/unloading, were identified during this period, which correlate well 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. These results show that the dynamics in the middle magnetosphere are coupled with auroral variability. ©2019. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailAcceleration of Ions in Jovian Plasmoids: Does Turbulence Play a Role?
Kronberg, Elena A.; Grigorenko, Elena Evgenevna; Malykhin, Andrei Yu et al

in Journal of Geophysical Research. Space Physics (2019)

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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 detailThe polar region of Jupiter’s aurora : barcode noise, conjugate flares and more...
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gladstone, Randy et al

Conference (2018, July 11)

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 ... [more ▼]

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 nm range, to explore the polar physics in two very different ways. In the first part of this presentation, we will analyze the rapid variations of the background noise caused by >10MeV electrons penetrating the instrument. In UV images, this rapidly varying signal takes the form of a barcode-like pattern. We will discuss the mapping, the altitude and the characteristic timescale of the “barcode events” in order to constrain the mechanisms giving rise to them. In the second part, we will compare simultaneous observations of the aurorae from the two hemispheres. One dataset comes from Juno-UVS while the other comes from the Hubble Space Telescope STIS instrument. We will show that most auroral features in one hemisphere have a clear counterpart in the other one. Among other examples, we will show evidence of conjugate flares in the active region of the two hemispheres. However, other strong brightness enhancements only show up in one hemisphere, without any echo in the other one. [less ▲]

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