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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 ▲]

Detailed reference viewed: 45 (6 ULiège)
See detailJUNO/MWR's supportive observations of downward field-aligned MeV electrons at Jupiter
Santos-Costa, Daniel; Kurth, William; Hospodarsky, George et al

in 42nd COSPAR Scientific Assembly (2018, July 01)

Since August 2016, the Juno MicroWave Radiometer (MWR) has continuously measured the radiation emitted by Jupiter and the surrounding environment, over a frequency range from 0.6 to 22 GHz, from Juno's ... [more ▼]

Since August 2016, the Juno MicroWave Radiometer (MWR) has continuously measured the radiation emitted by Jupiter and the surrounding environment, over a frequency range from 0.6 to 22 GHz, from Juno's highly elliptical 53-day polar orbit about Jupiter. The contributors to the strongest radio signals at the shorter frequencies are the thermal, cosmic microwave background, and synchrotron emission produced by the inner electron belt. Weaker but perceptible signatures in MWR are also reported at the shortest frequency during perijove 1 (PJ1) and PJ3-PJ11. Some of them are identified as a source of synchrotron emission produced by downward field-aligned MeV electrons in the middle magnetosphere. In this paper, we present a synthesis of the spatial distributions of the microwave radiation observed at six wavelengths. We focus on synchrotron emissions originating from regions beyond Io's plasma torus that we believe to be linked to auroral activity. To support our findings, we discuss the results of a multi-instrument analysis of radio (MWR, WAVES), field (Juno magnetometer), extreme and far-ultraviolet auroral emission (Juno/UVS), plasma and energetic electron (JADE, JEDI) datasets, and background radiation signatures in Juno's ASC instrument for PJ1. Our data analysis raises the question how electrons with energies of 10's of MeV are populating, transported, and accelerated within the middle magnetosphere to become part of the auroral current circuit at Jupiter. [less ▲]

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See detailLimb observations of H3+ in the mid- and low latitude Jovian atmosphere with the JIRAM spectrometer
Migliorini, Alessandra; Atreya, Sushil K.; Grassi, Davide et al

Conference (2018)

The Jupiter Infrared Auroral Mapper (JIRAM) instrument, onboard the NASA's Juno mission, is composed of a camera in the L and M bands, and a spectrometer covering the 2-5 μm region. During the period from ... [more ▼]

The Jupiter Infrared Auroral Mapper (JIRAM) instrument, onboard the NASA's Juno mission, is composed of a camera in the L and M bands, and a spectrometer covering the 2-5 μm region. During the period from August 2016 to March 2017, when five mission flybys were completed, it was possible to observe with JIRAM the Jupiter's atmosphere in a very slant perspective, allowing sampling the stratosphere at different altitudes.We took advantage of H^{+}_{3} emissions in the 3-4 μm spectral band, observed with JIRAM in the above reported period, to retrieve the H3+ densities and temperatures, through the inversion method described in Dinelli et al. (2017), at altitudes from 200 to 700 km above the 1-bar level, and in the latitude region from 60° equatorward, in both hemispheres.Retrieved volume mixing ratios are on average higher in the Southern hemisphere than in the Northern, in accordance with previous observations in the auroral region (Adriani et al. 2017).Temperature values increase quite uniformly with altitude in both hemispheres, and are generally in agreement with temperature fields retrieved with Cassini/CIRS at 200-300 km (Sinclair et al. 2017). Finally, H3+ concentrations decrease from about 106 mol/cm^{3} at 200-300 km to 3x10^{5} mol/cm^{3} at 600 km.Although the coverage of analysed data does not allow investigating the H^{+}_{3} variability with respect to local time, the available data potentially allow to retrieve a 3-dimensional structure of the atmosphere in the 200-700 km altitude range, which has not been well addressed by previous ground- based and space observations. [less ▲]

Detailed reference viewed: 17 (2 ULiège)
See detailElectron Pitch Angle Distributions Along Field Lines Connected to the Auroral Region from ~25 to ~1.2 RJ Measured by the Jovian Auroral Distributions Experiment-Electrons (JADE-E) on Juno
Allegrini, Frederic; Bagenal, Fran; Bolton, Scott J et al

Poster (2017, December 13)

The Jovian Auroral Distributions Experiment (JADE) on Juno provides critical in situ measurements of electrons and ions needed to understand the plasma distributions and processes that fill the Jovian ... [more ▼]

The Jovian Auroral Distributions Experiment (JADE) on Juno provides critical in situ measurements of electrons and ions needed to understand the plasma distributions and processes that fill the Jovian magnetosphere and ultimately produce Jupiter’s bright and dynamic aurora. JADE is an instrument suite that includes two essentially identical electron sensors (JADE-Es) and a single ion sensor (JADE-I). JADE-E measures electron energy distributions from ~0.1 to 100 keV and provides detailed electron pitch angle distributions (PAD) at ~7.5° resolution. Juno’s trajectories in the northern hemisphere have allowed JADE to sample electron energy and pitch angle distributions on field lines connected to the auroral regions from as close as ~1.2 RJ all the way to distances greater than 25 RJ. Here, we report on the evolution of these distributions. Specifically, the PADs change from mostly uniform at distances greater than ~20 RJ, to butterfly from ~18 to ~12 RJ, to field aligned or pancake, depending on the energy, closer to Jupiter. Below ~1.5 RJ, electron beams and loss cones are observed. [less ▲]

Detailed reference viewed: 27 (2 ULiège)
See detailJuno-UVS observation of the Io footprint: Influence of Io’s local environment and passage into eclipse on the strength of the interaction
Hue, Vincent; Gladstone, Randy; Greathouse, Thomas K et al

Poster (2017, December 13)

The Juno mission offers an unprecedented opportunity to study Jupiter, from its internal structure to its magnetospheric environment. Juno-UVS is a UV spectrograph with a bandpass of 70<λ<205 nm, built to ... [more ▼]

The Juno mission offers an unprecedented opportunity to study Jupiter, from its internal structure to its magnetospheric environment. Juno-UVS is a UV spectrograph with a bandpass of 70<λ<205 nm, built to characterize Jupiter’s UV emissions and provide remote sensing capacities for the onboard fields and particle instruments (MAG, Waves, JADE and JEDI). Juno’s orbit allows observing Jupiter from a unique vantage point above the poles. In particular, UVS has observed the instantaneous Io footprint and extended tail as Io enters into eclipse. This observation may better constrain whether the atmosphere of Io is sustained via volcanic activity or sublimation. Among other processes, the modulation of Io’s footprint brightness correlates to the strength of the interaction between the Io plasma torus and its ionosphere, which, in turn, is likely to be affected by the atmospheric collapse. UVS observed the Io footprint during two eclipses that occurred on PJ1 and PJ3, and one additional eclipse observation is planned during PJ9 (24 Oct. 2017). We present how the electrodynamic coupling between Io and Jupiter is influenced by changes in Io’s local environment, e.g. Io’s passage in and out of eclipse and Io’s traverse of the magnetodisc plasma sheet. [less ▲]

Detailed reference viewed: 26 (3 ULiège)
See detailSystematic capture of MeV electron beams by MWR
Santos-Costa, Daniel; Bellotti, Amadeo; Janssen, Mike et al

Poster (2017, December 13)

Every ~ 53 days since August 2016, Juno swings by Jupiter and as the spacecraft spins along a polar orbit, measurements of Jupiter's microwave radiation are carried out at high data rates for several ... [more ▼]

Every ~ 53 days since August 2016, Juno swings by Jupiter and as the spacecraft spins along a polar orbit, measurements of Jupiter's microwave radiation are carried out at high data rates for several hours (~ 9 hours) with the Juno Microwave Radiometer (MWR). Within ~ 6 planetary radii (Rj) and from inside/outside the magnetospheric region, the thermal and synchrotron emissions are measured at high temporal and spatial resolutions. In this paper, we present a synthesis of the spatial distributions of the microwave radiation and discuss the similarities and differences observed at six wavelengths (1.3-50 cm). In addition to the thermal emission and synchrotron radiation from Jupiter's electron belt, unexpected signatures in MWR are either systematically or sporadically reported during perijove 1 (PJ1) and PJ3-PJ6. The preliminary results of a multi-instrument analysis of radio (MWR), extreme and far-ultraviolet auroral emissions (Juno UVS), field (Juno magnetometer), keV electrons (JEDI), and background radiation signatures in Juno's ASC and SRU instruments suggest that some of these signatures are consistent with the capture by MWR of synchrotron emission radiated by MeV electron beams, which may be associated with auroral activity. We subsequently describe in detail our data analysis and effort to model the synchrotron radiation from MeV electron beams to support our findings. [less ▲]

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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 ▲]

Detailed reference viewed: 38 (13 ULiège)
See detailA comparative examination of auroral acceleration processes at Jupiter and Earth as enabled by the Juno mission to Jupiter
Mauk, Barry; Haggerty, Dennis; Paranicas, Chris et al

Conference (2017, December 12)

Particle distributions observed by Juno’s Energetic Particle Detector Investigation (JEDI) at low altitudes over Jupiter’s polar regions are exceedingly diverse in directionality and in the shapes of ... [more ▼]

Particle distributions observed by Juno’s Energetic Particle Detector Investigation (JEDI) at low altitudes over Jupiter’s polar regions are exceedingly diverse in directionality and in the shapes of their 3-dimensional energy distributions. Asymmetric, bi-directional angular beams with broad energy distributions are often observed near Jupiter’s main auroral oval with considerable variability as to whether upward or downward intensities are the strongest. Signatures of upward and downward magnetic field-aligned potentials, with inferred potentials up to 100’s of kV are sometimes observed, but unlike at Earth, these potentials do not seem to be associated with the strongest discrete-like auroral emission intensities. Particle distributions have similarities to those observed at Earth over the various phenomenological auroral emission regions, but they are observed in unexpected places with respect to the strongest auroral emission regions, and the jovian distributions are much more energetic. We present a comparative examination of auroral acceleration processes observed at Earth and Jupiter in relation to the respective auroral emission regions. [less ▲]

Detailed reference viewed: 31 (1 ULiège)
See detailAn overview of the first year of observations of Jupiter’s auroras by Juno-UVS with multi-wavelength comparisons
Gladstone, Randy; Greathouse, Thomas K; Versteeg, Maarten H et al

Conference (2017, December 12)

Juno’s Ultraviolet Spectrograph (Juno-UVS) has observed the Jovian aurora during eight perijove passes. UVS typically observes Jupiter for 10 hours centered on closest approach in a series of swaths, with ... [more ▼]

Juno’s Ultraviolet Spectrograph (Juno-UVS) has observed the Jovian aurora during eight perijove passes. UVS typically observes Jupiter for 10 hours centered on closest approach in a series of swaths, with one swath per Juno spin (~30s). During this period the spacecraft range to Jupiter’s aurora decreases from ~6 RJ to ~0.3 RJ (or less) in the north, and then reverses this in the south, so that spatial resolution changes dramatically. A scan mirror is used to target different features or raster across the entire auroral region. Juno-UVS observes a particular location for roughly 17 ms/swath, so the series of swaths provide snapshots of ultraviolet auroral brightness and color. A variety of forms and activity levels are represented in the Juno-UVS data–some have been described before with HST observations, but others are new. One interesting result is that the color ratio, often used as a proxy for energetic particle precipitation, may instead (in certain regions) indicate excitation of H2 by low-energy ionospheric electrons. Additional results from comparisons with simultaneous observations at x-ray, visible, and near-IR wavelengths will also be presented. [less ▲]

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See detailA Study of Local Time Variations of Jupiter’s Ultraviolet Aurora using Juno-UVS
Greathouse, Thomas K; Gladstone, Randy; Versteeg, Maarten H et al

Conference (2017, December 12)

Juno’s Ultraviolet Spectrograph (Juno-UVS) offers unique views of Jupiter’s auroras never before obtained in the UV, observing at all local times (unlike HST observations, limited to the illuminated disk ... [more ▼]

Juno’s Ultraviolet Spectrograph (Juno-UVS) offers unique views of Jupiter’s auroras never before obtained in the UV, observing at all local times (unlike HST observations, limited to the illuminated disk). With Juno’s 2-rpm spin period, the UVS long slit rapidly scans across Jupiter observing narrow stripes or swaths of Jupiter’s poles, from 5 hours prior to perijove until 5 hours after perijove. By rotating a mirror interior to the instrument, UVS can view objects from 60 to 120 degrees off the spacecraft spin axis. This allows UVS to map out the entire auroral oval over multiple spins, even when Juno is very close to Jupiter. Using the first 8 perijove passes, we take a first look for local time effects in Jupiter’s northern and southern auroras. We focus on the strength of auroral oval emissions and polar emissions found poleward of the main oval. Some unique polar emissions of interest include newly discovered polar flare emissions that start off as small localized points of emission but quickly (10’s of sec) evolve into rings. These emissions evolve in such a way as to be reminiscent of raindrops striking a pond. [less ▲]

Detailed reference viewed: 30 (3 ULiège)
See detailParticle energization and structuring of Jupiter’s main auroral oval as diagnosed with Juno measurements of (>30 keV) energetic particles
Mauk, Barry; Haggerty, Dennis; Paranicas, Chris et al

Conference (2017, June 14)

Juno polar low-altitude energetic particle observations indicate that the most intense emissions from Jupiter’s main auroral oval are caused by the impingement onto the atmosphere of relatively flat ... [more ▼]

Juno polar low-altitude energetic particle observations indicate that the most intense emissions from Jupiter’s main auroral oval are caused by the impingement onto the atmosphere of relatively flat, energy-monotonic electron distributions, often extending to energies >1 MeV. They can be associated with bi-directional angular beaming with upward fluxes greater than the downward fluxes. Downward fluxes of >800 mW/m^2 have been observed. However, when viewed in high time resolution ( 1.0s) these distributions are sometimes (3 of 8)) intermixed with >50keV downward accelerated electron distributions with the classic inverted-V configuration, indicative of steady magnetic field-aligned electric fields. The highest downward energy peak observed so far is 400 keV. The inverted-V energy distributions lack the high energy tails observed in adjacent regions, and thus, contrary to what is observed at Earth, the associated downward energy fluxes are generally lower than the downward energy fluxes associated with the more intense energy-monotonic distributions. The relationship between these two modes of auroral particle energization is unclear. Do the classic auroral processes that create inverted-V distributions become so powerful that instabilities are stimulated that cause stochastic energization to turn on and dominate, or do these two different forms of auroral acceleration represent distinctly different processes? These and other questions are explored. [less ▲]

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See detailThe Jovian UV aurorae as seen by Juno-UVS
Bonfond, Bertrand ULiege; Gladstone, Randy; Grodent, Denis ULiege et al

Conference (2017, April 26)

The Juno spacecraft was inserted in orbit around Jupiter on July 4th 2016. Its highly elongated polar orbit brings it <5000 km above the cloud tops every 53,5 days, allowing spectacular and unprecedented ... [more ▼]

The Juno spacecraft was inserted in orbit around Jupiter on July 4th 2016. Its highly elongated polar orbit brings it <5000 km above the cloud tops every 53,5 days, allowing spectacular and unprecedented views of its polar aurorae. The Juno-UVS instrument is an imaging spectrograph observing perpendicularly to the Juno spin axis. It is equipped with a moving scan mirror at the entrance of the instrument that allows the field of view to be directed up to +/-30° away from the spin plane. The 70-205 nm bandpass comprises key UV auroral emissions such as the H2 bands and the H Lyman alpha line, as well as hydrocarbon absorption bands. We present polar maps of the aurorae at Jupiter for the first three first few periapses. These maps offer the first high resolution observations of the night-side aurorae. We will discuss the observed auroral morphology, including the satellite footprints, the outer emissions, the main emission and the polar emissions. We will also show maps of the color ratio, comparing the relative intensity of wavelengths subject to different degrees of absorption by CH4. Such measurements directly relate to the energy of the precipitating particles, since the more energetic the particles, the deeper they penetrate and the stronger the resulting methane absorption. For example, we will show evidence of longitudinal shifts between the brightness peaks and color ratio peaks in several auroral features. Such shifts may be interpreted as the result of the differential particle drift in plasma injection signatures. [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 detailThe complex behavior of the satellite footprints at Jupiter: the result of universal processes?
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; 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 ▲]

Detailed reference viewed: 37 (8 ULiège)