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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 detailSTAR General Assembly February 2019
Grodent, Denis ULiege

Scientific conference (2019, February 04)

Report of the STAR research unit General Assembly during the Second STAR Workshop.

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

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

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

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

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See detailFlying through a Dawn Storm : an analysis of Juno-UVS images during PJ11
Bonfond, Bertrand ULiege; Gladstone, G. R.; Grodent, Denis ULiege et al

Poster (2018, December 11)

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at ... [more ▼]

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at Jupiter. An event with a total power emitted by the UV aurora in excess of 8.5 TW was even observed by Hisaki and the Hubble Space Telescope on May 21st 2016, during Juno’s approach of Jupiter. On February 7th 2018 (perijove 11, or PJ11), Juno’s ultraviolet imaging spectrograph, called Juno-UVS, observed the development of such a dawn storm, right before Juno flew right through the magnetic field line connected to this feature. The storm started around 13:15 UT as a limited enhancement of the main emission around midnight before slowly migrating and expanding on the dusk flank. As the brightness increased, the arc began to thicken and fork into two separate arcs. Simultaneously, the signatures of methane absorption of the UV light progressively intensified, indicative of a precipitation of increasingly energetic particles. Then, around 18:15 UT, Juno entered the field lines feeding the dawn storm. The remote auroral observations thus provide extremely valuable context information for the in-situ radio waves, particle and magnetic field observations gathered at this time. [less ▲]

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

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

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

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10° to 120° along the footprint tail. Juno's suite of magnetospheric instruments acquired detailed measurements of the Io footprint tail. Juno observed planetward electron energy fluxes of 70 mW/m2 near the Io footprint, and 10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Observed waves were primarily below the proton cyclotron frequency, yet identification of a definitive wave mode is elusive. Beyond 40° down the footprint tail, Juno observed depleted upward loss cones, suggesting the broadband acceleration occurred at distances beyond Juno's transit distance of 1.3 to 1.7 RJ. For all transits, Juno observed fine structure on scales of 10s km, and confirmed independently with electron and waves measurements that a bifurcated tail can intermittently exist. [less ▲]

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See detailObservations of Jupiter by the Juno Ultraviolet Spectrograph (Juno-UVS)
Greathouse, T. E.; Gladstone, G.R.; Hue, V. et al

Conference (2018, September 20)

We present an overview of the science performed by Juno’s Ultraviolet Spectrograph, UVS, over the first 11 successful perijove sequences performed since orbital insertion on July 4th, 2016. We will ... [more ▼]

We present an overview of the science performed by Juno’s Ultraviolet Spectrograph, UVS, over the first 11 successful perijove sequences performed since orbital insertion on July 4th, 2016. We will discuss the measured local time dependence of Jupiter’s polar auroral emissions, simultaneous UV and H3+ observations and their correlations or lack thereof, evolution and morphology of Io’s magnetic footprint in Jupiter’s atmosphere, measurements concerning the spatial and temporal variation of high energy particles (>7 MeV) in the polar regions of Jupiter’s magnetosphere, and finally the production of a dataset that could be used to produce an all sky UV stellar atlas at wavelengths between 70 and 205 nm. [less ▲]

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See detailA chemical survey of exoplanets with ARIEL
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in Experimental Astronomy (2018)

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the ... [more ▼]

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet's birth, and evolution. ARIEL was conceived to observe a large number ( 1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H[SUB]2[/SUB]O, CO[SUB]2[/SUB], CH[SUB]4[/SUB] NH[SUB]3[/SUB], HCN, H[SUB]2[/SUB]S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed - using conservative estimates of mission performance and a full model of all significant noise sources in the measurement - using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL - in line with the stated mission objectives - will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives. [less ▲]

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See 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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See detailAuroral storm and polar arcs at Saturn
Palmaerts, Benjamin ULiege; Radioti, Aikaterini ULiege; Grodent, Denis ULiege et al

Conference (2018, July 11)

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph (UVIS ... [more ▼]

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini observed Saturn's northern aurora for about 14h. In this final UVIS sequence, several auroral structures appear, revealing processes occurring simultaneously in Saturn's magnetosphere. A poleward expansion and a brightening of the main emission dawn arc, a phenomenon known as an auroral storm, suggests that an intense flux closure process took place in the magnetotail through magnetic reconnection. This magnetotail reconnection and the associated field dipolarization generated signatures in the auroral, magnetic field, and plasma wave data. The enhanced magnetotail reconnection is likely caused by a compression of the magnetosphere induced by the arrival at Saturn of an interplanetary coronal mass ejection. In addition to the auroral storm, a polar arc observed on the duskside was tracked for the first time from the start of its growth phase until its quasi disappearance, providing evidence of its formation process. This polar arc is a proxy for the location of reconnection sites on the dayside magnetosphere and for the orientation of the interplanetary magnetic field. Finally, the atypical observation of one of the most polar auroral arcs ever reported at Saturn supports the scenario of an interplanetary shock arriving at Saturn at the end of the Cassini mission. In that respect, the ultimate UVIS auroral sequence allowed us to capture dynamical aspects of Saturn’s magnetosphere not frequently or even never observed in the past. [less ▲]

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See detailCassini UVIS Observations of Saturn's Auroras and Polar Haze
Pryor, W.R.; West, R.A.; Jouchoux, A. et al

Poster (2018, July)

In 2016 and 2017, the Cassini Saturn Orbiter executed a final series of high inclination, low- periapsis orbits ideal for studying Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph ... [more ▼]

In 2016 and 2017, the Cassini Saturn Orbiter executed a final series of high inclination, low- periapsis orbits ideal for studying Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) obtained an extensive set of auroral images of both poles, some at the highest spatial resolution obtained during Cassini's long orbital mission (2004-2017). In some cases, two or three spacecraft slews at right angles to the long slit of the spectrograph were required to cover the entire auroral region to form images of auroral H2 and H emission. The long wavelength part of the northern UVIS polar images contains a signal from reflected sunlight with absorption signatures of acetylene and other Saturn hydrocarbons. Saturn's UV-dark polar hexagon is now seen in the new UVIS long- wavelength data, surrounded by a circular collar that is less dark. There is a definite spatial relationship between the UV-bright auroras and the dark material, with the dark material concentrated under or just inside of the main auroral oval. The outer dark collar roughly corresponds with the previously reported weaker outer auroral oval (Grodent et al., 2011; Lamy et al., 2013). Time variations in the dark material are seen. The spectroscopy of the different regions will be discussed. As has been previously discussed using Voyager data (Lane et al., 1982, West et al., 1983, Pryor and Hord, 1991), Hubble data (Ben Jaffel et al., 1995; Gerard et al., 1995) and Cassini data (Sayanagi et al., 2018), Saturn's auroras appear to be generating, through both neutral and ion chemistry, UV-dark material that is probably composed of complex hydrocarbons. [less ▲]

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See detailJuno-UVS observations of Jupiter's aurora and airglow emissions
Gladstone, R.; Mura, A.; Kurth, W. et al

in 42nd COSPAR Scientific Assembly (2018, July)

The Ultraviolet Spectrograph (UVS) on Juno observes Jupiter's northern and southern auroras for several hours each during every perijove pass. On each pass the 7°-long slit of UVS is used to observe the ... [more ▼]

The Ultraviolet Spectrograph (UVS) on Juno observes Jupiter's northern and southern auroras for several hours each during every perijove pass. On each pass the 7°-long slit of UVS is used to observe the jovian aurora in a series of swaths, with one swath for each 30-s spin of the Juno spacecraft. During these perijove periods, the range of Juno to the aurora drops from ˜6 R_J to ˜0.3 R_J (or less) in the north - and then reverses this in the south - so that spatial resolution and coverage change dramatically. A scan mirror points the UVS boresight at up to 30° from the Juno spin plane to enable targeting of different features or to build up context images by rastering over the auroral region. In addition, during the time period between observations of the northern and southern auroral regions, low-latitude airglow observations are possible. Since Juno perijove altitudes are only 3500-8000 km above the cloud tops, UVS is able to study Jupiter's airglow from within Jupiter's upper atmosphere. A variety of auroral forms and activity levels can be identified in the Juno-UVS data; some of these have been described before with HST observations, but others are new. One new result is that a large expanse of polar emissions may be excited by low-energy ionospheric electrons (and thus would be unrelated to precipitating particles). Recent results and comparisons with simultaneous Chandra observations at x-ray wavelengths will be presented here. In addition, we will also report on UVS airglow observations to date, with special attention to the Lyα emissions of atomic hydrogen. [less ▲]

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See detailExploring Jupiter's Aurorae with the Chandra and XMM-Newton X-ray Observatories
Dunn, W.; Ray, L.; Kraft, R. et al

in 42nd COSPAR Scientific Assembly (2018, July)

Jupiter's polar X-ray aurora is dominated by a bright dynamic hot spot that is produced by precipitating 10 MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These ... [more ▼]

Jupiter's polar X-ray aurora is dominated by a bright dynamic hot spot that is produced by precipitating 10 MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These highly energetic emissions exhibit pulsations over timescales of 10s of minutes and change morphology, intensity and precipitating particle populations from observation to observation and pole to pole [e.g. Dunn et al. 2017]. Surrounding the soft X-ray emission there is an oval of hard X-ray bremsstrahlung from precipitating electrons. The acceleration process/es that allow Jupiter to produce these high-energy X-ray emissions remain poorly understood, but vary with solar wind conditions [Dunn et al. 2016; Kimura et al. 2016] and the soft X-ray emissions are expected to relate to processes on the boundary between Jupiter's magnetosphere and the solar wind.We present a decade of remote X-ray observations of Jupiter from 2007 to 2017 using the Earth-orbiting X-ray telescopes Chandra and XMM-Newton. We compare these high spatial and spectral resolution X-ray data with in-situ measurements of the solar wind and the Jovian magnetosphere conducted by NASA's New Horizons and Juno spacecraft. Analysing X-ray spectrograms and X-ray auroral videos we probe time-varying accelerations, precipitating particle populations and auroral morphologies and further connect these with their solar wind and in-situ drivers. Finally, we compare X-ray observations with UV observations to enrich multi-waveband connections and deepen our understanding of how Jupiter generates its highly energetic polar auroral precipitations. [less ▲]

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

Conference (2018, July)

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

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10 ̊ to 120 ̊ along the footprint tail. Juno’s suite of magnetospheric instruments allow for detailed measurements of a variety of physical parameters for the Io footprint tail. Juno observed planetward electron energy fluxes of ~70 mW/m2 near the Io footprint, and ~10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased down the tail. All observed electron distributions were broad in energy, possibly suggesting an Alfvénic acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Here, we discuss the JADE, UVS, Waves, and Magnetic field measurements taken during Juno’s transits through the Io footprint tail flux tubes during perijoves 5-7 and compare these measurements with existing theoretical models describing the tail formation. [less ▲]

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See detailGemini-TEXES mid-infrared spectral observations of Jupiter's auroral regions: comparison with ultraviolet and near-infrared observations
Sinclair, J. A.; Orton, G. S.; Greathouse, T. K. et al

Conference (2018, July)

Jupiter exhibits auroral emission over a large range of wavelengths. Auroral emission at X-ray, ultraviolet and near-infrared wavelengths demonstrate the precipitation of ion and electrons in Jupiter’s ... [more ▼]

Jupiter exhibits auroral emission over a large range of wavelengths. Auroral emission at X-ray, ultraviolet and near-infrared wavelengths demonstrate the precipitation of ion and electrons in Jupiter’s upper atmosphere, at altitudes exceeding 350 km above the 1-bar level. Enhanced mid-infrared emission of stratospheric CH4, C2H2, C2H4 and further hydrocarbons is also observed coincident with Jupiter’s auroral regions. On March 17-19th 2017, we obtained spectral measurements of H2 S(1), CH4, C2H2, C2H4 and C2H6 emission of Jupiter’s high latitudes using TEXES on Gemini-North. This rare opportunity combines both the superior spectral resolving power of TEXES (R ≤ 85000) and the high-spatial diffraction-limited resolution (~2° latitude-longitude footprint at 70°N) provided by Gemini-North’s 8-metre primary aperture. The high spatial resolution has for the first time revealed transient spatial structure in the emission of CH4, C2H2 and C2H4 in Jupiter’s northern auroral region. From March 17th to 19th 2017, during a solar wind compression, a duskside brightening of these species was observed in the northern auroral region. We will present a retrieval analysis of these observations to demonstrate the altitudes in the atmosphere and the magnitude over which temperatures and hydrocarbon abundances were modified during this event. We will also compare the morphology of the mid-infrared emission with near-simultaneous (i) HST-STIS images of the ultraviolet auroral emission and (ii) IRTF-SpeX observations of the 3.42-μ m H3+ emission. [less ▲]

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See detailStereoscopic observations of Jovian decametric radio arc s associated with ultraviolet auroras
Imai, Masafumi; Kurth, W.S.; Bonfond, Bertrand ULiege et al

Conference (2018, July)

Auroras in Jupiter’s polar regions show complex activity over a broad range of electromagnetic wavelengths. One of the auroral radio components, decametric radiation (DAM), dominates the frequency range ... [more ▼]

Auroras in Jupiter’s polar regions show complex activity over a broad range of electromagnetic wavelengths. One of the auroral radio components, decametric radiation (DAM), dominates the frequency range from a few to 40 MHz and is produced at a frequency very close to the local electron cyclotron frequency. Since Juno first began detecting sporadic DAM arcs on May 5, 2016, during the approach to Jupiter, the DAM radio arcs have been monitored in a frequency range of 3.5 to 40.5 MHz by several observatories. These include Juno at Jupiter, Cassini at Saturn, STEREO A at 1 AU, WIND at Earth, and Earth-based radio observatories (Long Wavelength Array Station One (LWA1) in New Mexico, USA, and Nançay Decameter Array (NDA) in France). We have carried out a visual survey of the spectral data to identify concurrent DAM radio arcs, from May 5, 2016, through September, 2017 (Cassini’s end-of-mission). We found six events for which two or more observers clearly captured the same group of arcs. In one of the events on December 3, 2016, Juno first captured a group of the DAM arcs around 4:00 UT and two intense arcs were later recorded in NDA spectrograms at 6:30 and 7:45 UT. On the same day from 13:44 to 14:24 UT, the Hubble Space Telescope (HST) observed a bright auroral arc at ultraviolet wavelengths with an emitted power of 20 to 25 GW, suggesting a possible link to the concurrently observed DAM arcs. In this paper, we show results from the stereoscopic DAM radio observations and compare with the ultraviolet auroras captured by HST. [less ▲]

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See detailCombined Juno observations and modeling of the Jovian auroral electron interaction with the Jovian upper atmosphere
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Gladstone, G.R. et al

Poster (2018, July)

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s ... [more ▼]

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s magnetic footprint. In addition, the ratio of the H2 spectral band absorbed by hydrocarbons to the unabsorbed portion of the spectrum (FUV color ratio) is often used as a proxy for the depth of the penetration of energetic electrons (relative to the hydrocarbon homopause). The relationship between the color ratio and the electron penetration has been simulated with a Monte Carlo model solving the Boltzmann transport equation. Analysis of concurrent FUV and IR images obtained during the first perijove (PJ1) suggests that the ratio of H3+ radiance to H2 unabsorbed emission is maximal in regions with low FUV color ratio. This result suggests that part of the H3+ column is lost in reactions with methane which converts H3+ into heavier ions. We also examine the observed relationship between the detailed morphology of the ultraviolet structures and of the associated UV color ratio, the total downward electron energy flux and its spectral characteristics. [less ▲]

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See detailCombined Juno observations and modeling of th e Jovian auroral electron interaction with the Jovian upper atmosphere
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Gladstone, George R. et al

Poster (2018, July)

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s ... [more ▼]

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s magnetic footprint. In addition, the ratio of the H2 spectral band absorbed by hydrocarbons to the unabsorbed portion of the spectrum (FUV color ratio) is often used as a proxy for the depth of the penetration of energetic electrons (relative to the hydrocarbon homopause). The relationship between the color ratio and the electron penetration has been simulated with a Monte Carlo model solving the Boltzmann transport equation. Analysis of concurrent FUV and IR images obtained during the first perijove (PJ1) suggests that the ratio of H3+ radiance to H2 unabsorbed emission is maximal in regions with low FUV color ratio. This result suggests that part of the H3+ column is lost in reactions with methane which converts H3+ into heavier ions. We also examine the observed relationship between the detailed morphology of the ultraviolet structures and of the associated UV color ratio, the total downward electron energy flux and its spectral characteristics. [less ▲]

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See detailJupiter’s mesmerizing auroral show (PJ13); HST ultraviolet observations near and far from Juno perijoves
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Palmaerts, Benjamin ULiege et al

Conference (2018, July)

After a 6-month period during which the separation angle between the Sun and Jupiter was too small to permit observations with Earth orbit telescopes, operation of the Hubble Space Telescope, supporting ... [more ▼]

After a 6-month period during which the separation angle between the Sun and Jupiter was too small to permit observations with Earth orbit telescopes, operation of the Hubble Space Telescope, supporting the Juno mission, was resumed (almost) in time for PJ11. We briefly review the main results of the previous part of this HST campaign, covering PJ03 to PJ07. We then present the newest results obtained during PJ11, PJ12 and PJ13. Most of the observing time allocated to this HST campaign was used during the first part of the campaign and allowed us to sample Jupiter’s aurora, not only near Juno’s perijoves, but also during the week before and the week after each perijove. During these times away from perijove, HST-STIS was the sole instrument able to provide high spatial and high temporal resolution dynamic images of Jupiter’s FUV aurora, which can be compared with measurements from Juno’s in situ instruments. Instead of presenting a statistical overview of the data, we have a more detailed look at some specific features revealed by the as yet unsurpassed STIS camera. In particular, we identify distinctive auroral phenomena, like explosive brightenings poleward of the main auroral emission. We present one such event, which we link to a strong perturbation of the magnetic field and of the energy distribution of the plasma particles concurrently observed with Juno. We suggest that the characteristics and the timing of this perturbation and of its associated auroral signature are consistent with a reconnection event. [less ▲]

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