On the Relation Between Jovian Aurorae and the Loading Unloading of the Magnetic Flux Simultaneous Measurements from Juno HST and Hisaki Invited (original) (raw)
HST-Juno synergistic approach of Jupiter's magnetosphere and ultraviolet auroras
2016
Dr. G. Randall Gladstone (CoI) Southwest Research Institute rgladstone@swri.edu Prof. John T. Clarke (CoI) (AdminUSPI) Boston University jclarke@bu.edu Dr. Bertrand Bonfond (CoI) (ESA Member) Universite de Liege b.bonfond@ulg.ac.be Prof. Jean-Claude M. Gerard (CoI) (ESA Member) Universite de Liege jc.gerard@ulg.ac.be Dr. Aikaterini Radioti (CoI) (ESA Member) Universite de Liege a.radioti@ulg.ac.be Dr. Jonathan David Nichols (CoI) (ESA Member) University of Leicester jdn4@le.ac.uk Dr. Emma J. Bunce (CoI) (ESA Member) University of Leicester ejb10@ion.le.ac.uk Dr. Lorenz Roth (CoI) (ESA Member) Royal Institute of Technology lorenzr@kth.se Dr. Joachim Saur (CoI) (ESA Member) Universitat zu Koeln saur@geo.uni-koeln.de Dr. Tomoki Kimura (CoI) RIKEN Wako Institute tomoki.kimura@riken.jp Dr. Glenn S. Orton (CoI) Jet Propulsion Laboratory glenn.s.orton@jpl.nasa.gov Dr. Sarah V. Badman (CoI) (ESA Member) Lancaster University s.badman@lancaster.ac.uk Dr. Barry Mauk (CoI) The Johns Hopkins Uni...
Auroral signatures of flow bursts released during magnetotail reconnection at Jupiter
Journal of Geophysical Research, 2010
1] Recent studies based on Hubble Space Telescope (HST) data reported the presence of transient polar dawn spots in the Jovian auroral region and interpreted them as signatures of internally driven magnetic reconnection in the Jovian magnetotail. Even though an association of the polar dawn spots with the reconnection process has been suggested, it has not been yet investigated which part of the process and what mechanism powers these auroral emissions. In the present study, we examine the scenario that the auroral spots are triggered by the inward moving flow bursts released during magnetic reconnection at Jupiter. We base our analysis on a model adapted from the terrestrial case, according to which moving plasma flow burst is coupled with the ionosphere by field-aligned currents, giving rise to auroral emissions. We estimate the upward field-aligned current at the flank of the flow bursts, using in-situ magnetic field measurements and we derive the auroral emitted power. We statistically study the observed emitted power of the polar dawn spots, based on HST data from 1998 to 2007, and we compare it with the emitted power derived according to the proposed scenario. Apart from the emitted power, other properties of the polar dawn spots such as their location, periodicity, duty cycle and multiplicity suggest that they are associated with the inward moving flow bursts released during magnetic reconnection in Jupiter's tail. Citation: Radioti, A., D. Grodent, J.-C. Gérard, and B. Bonfond (2010), Auroral signatures of flow bursts released during magnetotail reconnection at Jupiter,
Improved mapping of Jupiter's auroral features to magnetospheric sources
Journal of Geophysical Research, 2011
1] The magnetospheric mapping of Jupiter's polar auroral emissions is highly uncertain because global Jovian field models are known to be inaccurate beyond ∼30 R J . Furthermore, the boundary between open and closed flux in the ionosphere is not well defined because, unlike the Earth, the main auroral oval emissions at Jupiter are likely associated with the breakdown of plasma corotation and not the open/closed flux boundary in the polar cap. We have mapped contours of constant radial distance from the magnetic equator to the ionosphere in order to understand how auroral features relate to magnetospheric sources. Instead of following model field lines, we map equatorial regions to the ionosphere by requiring that the magnetic flux in some specified region at the equator equals the magnetic flux in the area to which it maps in the ionosphere. Equating the fluxes in this way allows us to link a given position in the magnetosphere to a position in the ionosphere. We find that the polar auroral active region maps to field lines beyond the dayside magnetopause that can be interpreted as Jupiter's polar cusp; the swirl region maps to lobe field lines on the night side and can be interpreted as Jupiter's polar cap; the dark region spans both open and closed field lines and must be explained by multiple processes. Additionally, we conclude that the flux through most of the area inside the main oval matches the magnetic flux contained in the magnetotail lobes and is probably open to the solar wind.
Magnetic field influence on aurorae and the Jovian plasma disk radial structure
Annales Geophysicae, 2006
The Jovian paraboloid magnetospheric model is applied for the investigation of the planet's auroral emission and plasma disk structure in the middle magnetosphere. Jupiter's auroral emission demonstrates the electrodynamic coupling between the ionosphere and magnetosphere. For comparison of different regions in the ionospheric level and in the magnetosphere, the paraboloid model of the global magnetospheric magnetic field is used. This model provides mapping along highly-conducting magnetic field lines. The paraboloid magnetic field model is also applied for consideration of the stability of the background plasma disk in the rotating Jupiter magnetosphere with respect to the flute perturbations. Model radial distribution of the magnetic field and experimental data on the plasma angular velocity in the middle Jovian magnetosphere are used. A dispersion relation of the plasma perturbations in the case of a perfectly conducting ionosphere is obtained. Analyzing starting conditions of a flute instability in the disk, the "threshold" radial profile of the plasma density is determined. An application of the results obtained to the known data on the Jovian plasma disk is discussed.
Auroral evidence of a localized magnetic anomaly in Jupiter's northern hemisphere
Journal of Geophysical Research, 2008
1] We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede form individual footpaths, which are fitted with three reference contours. The satellite footprints provide a convenient mapping between the northern Jovian ionosphere and the equatorial plane in the middle magnetosphere, independent of any magnetic field model. The VIP4 magnetic field model is in relatively good agreement with the observed footprint of Io. However, in the auroral kink sector, between the 80°and 150°System III meridians, the model significantly departs from the observation. One possible way to improve the agreement between the VIP4 model and the observed footprints is to include a magnetic anomaly. We suggest that this anomaly is characterized by a weakening of the surface magnetic field in the kink sector and by an added localized tilted dipole field. This dipole rotates with the planet at a depth of 0.245 R J below the surface, and its magnitude is set to $1% of Jupiter's dipole moment. The anomaly has a very limited influence on the magnetic field intensity in the equatorial plane between the orbits of Io and Ganymede. However, it is sufficient to bend the field lines near the high-latitude atmosphere and to reproduce the observed satellite ultraviolet footpaths. JUNO's in situ measurements will determine the structure of Jupiter's magnetic field in detail to expand on these results.
Auroral evidence of Io's control over the magnetosphere of Jupiter
Geophysical Research Letters, 2012
1] Contrary to the case of the Earth, the main auroral oval on Jupiter is related to the breakdown of plasma corotation in the middle magnetosphere. Even if the root causes for the main auroral emissions are Io's volcanism and Jupiter's fast rotation, changes in the aurora could be attributed either to these internal factors or to fluctuations of the solar wind. Here we show multiple lines of evidence from the aurora for a major internally-controlled magnetospheric reconfiguration that took place in Spring 2007. Hubble Space Telescope far-UV images show that the main oval continuously expanded over a few months, engulfing the Ganymede footprint on its way. Simultaneously, there was an increased occurrence rate of large equatorward isolated auroral features attributed to injection of depleted flux tubes. Furthermore, the unique disappearance of the Io footprint on 6 June appears to be related to the exceptional equatorward migration of such a feature. The contemporary observation of the spectacular Tvashtar volcanic plume by the New-Horizons probe as well as direct measurement of increased Io plasma torus emissions suggest that these dramatic changes were triggered by Io's volcanic activity.
Geophysical Research Letters, 2019
Since the discovery of Jovian auroral radio emissions, the question arises of the source positions of the different components (broadband kilometric, hectometric, and decametric) and their association with far ultraviolet (FUV) auroral emissions. We surveyed Juno's first 15 perijoves to track local radio sources from in situ Juno/Waves measurements (50 Hz to 40 MHz). This allowed us to study the 3-D spatial distribution of the broadband kilometric, hectometric, and decametric radio sources. These sources are carried by the same magnetic field lines, with the bulk of them at apex M ranging from 15 to 60 (distance measured in R J at the magnetic equator). Finally, comparisons with images of the Jovian FUV aurorae simultaneously acquired by the Hubble Space Telescope (HST) reveal a partial spatial colocation of the FUV main oval emission with the identified local radio sources. Plain Language Summary Jupiter produces auroral emission at radio and far ultraviolet (FUV) wavelengths. These emissions have been studied for more than half a century, from an equatorial point of view. The Juno spacecraft, in orbit around Jupiter since July 2016, passes above the northern and southern poles once per orbit, and thus inside the regions where the auroral radio emission occurs. Using the first 15 Juno's orbits, we found that the sources, from the kilometer to the decameter wavelengths, are all colocated. The comparison with simultaneous images on the FUV wavelengths, acquired by the Hubble Space Telescope, reveals that the source of Jovian auroral radiation at the kilometer and decameter wavelengths are magnetically connected to region of FUV emissions.
Icarus
The Cassini magnetometer (MAG) has provided us with a rich and extensive dataset of magnetic field measurements, not only of Saturn's internal field but also the many and varied magnetospheric sources of field external to the planet. In this review, we will summarise the development of our understanding in the following main areas: (1) The apparently high degree of axial symmetry of the planet's internal field. (2) The ubiquitous 'planetary period oscillations' in the field, themselves a signature of rotating current systems likely driven by an atmospheric source. (3) The finite lifetime of 'fossil fields' in Titan's ionosphere, and the role of these fields as a signature of previous magnetic / plasma environments to which Titan has been exposed-with obvious application to transitions between magnetosphere and solar wind.
Journal of Geophysical Research: Space Physics, 2018
The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and measurements just recently available from Juno. For decades such relationships have been inferred from remote sensing observations of the Jovian aurora, primarily from the Hubble Space Telescope, and also more recently from Hisaki. However, to infer these quantities, remote sensing techniques had to assume properties of the Jovian atmospheric structure-leading to uncertainties in their profile. Juno's arrival and subsequent auroral passes have allowed us to obtain these relationships unambiguously for the first time, when the spacecraft passes through the auroral acceleration region. Using Juno/Jupiter Energetic particle Detector Instrument (JEDI), an energetic particle instrument, we present these relationships for the 30-keV to 1-MeV electron population. Observations presented here show that the electron energy flux in the loss cone is a nonlinear function of the characteristic or mean electron energy and supports both the predictions from Knight (1973,
Aurora on Jupiter: A Magnetic Connection with the Sun and the Medicean Moons
2010
Observational astronomy began in Padova four hunderd years ago, when Galileo Galilei pointed a newly invented instrument towards Jupiter. After only one week of observations he discovered four moons circling Jupiter. In the intervening four centuries, technical progress in instrumentation and novel observational approaches have revealed much about the connection between these Medicean moons with Jupiter, none more revealing than the auroral emissions. In this paper we review observations of ultraviolet aurora made by earth-orbitting spacecraft as well as those that flew by the Jovian system .
Reconnection and flows in the Jovian magnetotail as inferred from magnetometer observations
Journal of Geophysical Research, 2010
1] In Jupiter's magnetosphere, events such as flow bursts and changes to the magnetic field are thought to be driven predominantly by internal processes. Analysis of energetic particle data has established that flow bursts are associated with magnetic reconfiguration in the Jovian magnetotail. Here we use magnetometer data throughout the Jovian magnetotail to identify events that we relate to reconnection and flow. Using quantitative criteria, we have identified 249 reconnection events that are characterized by reversals or significant increases in B , the north-south component of the magnetic field, over background levels. We discuss the distribution of the events, their occurrence rate, and location inside or outside of a putative neutral line, as functions of radial distance and local time. Using the sign of B as a proxy for the flow direction, we establish the location of a statistical separatrix and find that its radial distance varies with local time. Where particle signatures of events in our data set have also been analyzed, they generally show increases of anisotropy. However, we have identified scores of additional events that have not been previously identified in the particle data; many of these new events occur in the premidnight local time sector. Finally, we examine our events for the 2-3 day periodicity that has been reported for flow bursts and auroral polar dawn spots and find that this periodicity is present only intermittently and is not statistically significant.
Model of the Jovian magnetic field topology constrained by the Io auroral emissions
Journal of Geophysical Research, 2011
The determination of the internal magnetic field of Jupiter has been the object of many studies and publications. These models have been computed from the Pioneer, Voyager and Ulysses measurements. Some models also use the position of the Io footprints as a constraint: the magnetic field lines mapping to the footprints must have their origins along Io's orbit. The use of this latter constraint to determine the internal magnetic field models greatly improved the modeling of the auroral emissions, in particular the radio ones which strongly depends on the magnetic field geometry. This constraint is, however, not sufficient for allowing a completely accurate modeling: The fact that the footprint field line should map to a longitude close to Io's was not used, so that the azimuthal component of the magnetic field could not be precisely constrained. Moreover, a recent study showed the presence of a magnetic anomaly in the northern hemisphere, which has never been included in any spherical harmonic decomposition of the internal magnetic field. We compute a decomposition of the Jovian internal magnetic field into spherical harmonics, which allows for a more accurate mapping of the magnetic field lines crossing Io, Europa and Ganymede orbits to the satellite footprints observed in UV. This model, named VIPAL, is mostly constrained by the Io footprint positions, including the longitudinal constraint, and normalized by the Voyager and Pioneer magnetic field measurements. We show that the surface magnetic fields predicted by our model are more consistent with the observed frequencies of the Jovian radio emissions, than those predicted by previous models.
2020
The dynamics of the Jovian magnetosphere is controlled by the interplay of the planet's fast rotation, its solar-wind interaction and its main Io plasma source. Magnetosphere-Ionosphere-Thermosphere (MIT) coupling processes controlling this interplay are significantly different from their Earth and Saturn counterparts. At the ionospheric level, they can be characterized by a set of key parameters (ionospheric conductances, electric currents and fields, exchanges of particles along field lines, Joule and particle energy deposition, etc.) from which one can determine (1) the closure of magnetospheric currents into the ionosphere, and (2) the net deposition/extraction of momentum and energy into/out of the upper atmosphere associated to MIT coupling. We present a method combining Juno multi-instrument data (MAG, JADE, JEDI, UVS, JIRAM and Waves) and modelling tools to provide preliminary estimates of these key parameters along the Juno's ionospheric magnetic footprints. We apply this method, as a first test, to the case of one particular main auroral oval crossing (PJ6-South) to present preliminary estimates of the ionospheric closure of magnetospheric field-aligned currents, of the resulting ionospheric conductances, currents and fields and of their control by electron precipitation. This synergistic use of data and models will be extended in the near future to a larger set of Juno orbits to progressively build a comprehensive view of MIT coupling at Jupiter and to provide a better determination of parameters not directly measured by Juno, such as the vertical structure of the Jovian upper atmosphere.
Plasma environment at the dawn flank of Jupiter's magnetosphere: Juno arrives at Jupiter
Geophysical Research Letters, 2017
This study examines the first observations from the Jovian Auroral Distributions Experiment (JADE) as the Juno spacecraft arrived at Jupiter. JADE observations show that Juno crossed the bow shock at 08:16 UT on 2016 day of year (DOY) 176 and magnetopause at 21:20 on DOY 177, with additional magnetopause encounters until 23:39 on DOY 181. JADE made the first detailed observations of the plasma environment just inside the dawn flank of the magnetopause. We find subcorotational ions and variable electron beaming, with multiple flux tubes of varying plasma properties. Ion composition shows a dearth of heavy ions; protons dominate the plasma, with only intermittent, low fluxes of O + /S ++ , along with traces of O ++ and S +++. We also find very little H þ 3 or He + , which are expected for an ionospheric plasma source. A few heavy ion bursts occur when the radial field nears reversal, but many other such reversals are not accompanied by heavy ions.
The Magnetosphere of Jupiter: Moving from Discoveries Towards Understanding
Bulletin of the AAS
The magnetosphere of Jupiter has been observed by many spacecraft, but most of these results have been discoveries of the global and general properties of the magnetosphere. They have typically raised more questions than they answered. Here we present some of the outstanding questions needed to truly understand Jupiter's magnetosphere and note that these questions can be answered by small, focused missions. Such missions are a fruitful place for collaboration between NASA's heliophysics and planetary science directorates. Past missions to Jupiter have made great discoveries about its magnetosphere, but for many reasons, those discoveries have raised more questions than they answered. To answer those questions and truly begin to understand this complex system, more observations and observations focused on key issues are necessary. Four open questions and unresolved problems out of a long list are: What is the origin of Jupiter's radiation belts? How and to what extent does the solar wind control of Jupiter's magnetosphere? What is the nature of reconnection at Jupiter and how does it control the dynamics of the magnetotail and magnetospheric boundaries? How does Jupiter's magnetosphere response to the variable volcanic output from Io? Jupiter's radiation belts are by far the most intense in the solar system and have been an enigma since they were discovered over half a century ago 1 . The radiation belts of Jupiter share some similarities with those of other planets. At the same time, they exhibit significant differences that are key to our understanding of the basic astrophysical processes of particle acceleration. Missions to Jupiter have shown us a host of transport, source and loss processes important in forming and sustaining the radiation belts; however, the decades old mystery pertaining to the energetics is still unresolved. Recent discoveries made by the Juno spacecraft, have put the spotlight on auroral processes as a means to generate high-energy ions and electrons that can fill Jupiter's vast magnetosphere 2,3 , including energetic ion conics 4 and upward ion beams 5 . We can reasonably suspect that they must play some role in the generation of energetic particles throughout Jupiter's inner magnetosphere. Unfortunately, Juno can only provide a limited amount of detail of the high-energy electrons (e.g. above the ~1 MeV limit of the Juno/JEDI instrument.) Many mysteries regarding the >1 MeV electrons still exists and understand their distribution at Jupiter has broad applications to particle acceleration in planetary and astrophysical systems. It is commonly assumed that Jupiter's magnetospheric dynamics are internally driven, by Jupiter's 10 hour rotation period and the volcanic activity of Io 6,7 . However, the extent to which the solar wind influences the magnetosphere is still under debate 9 , due in part to the lack of an upstream solar wind monitor on Jupiter. The solar wind directly influences the location of the Jovian bow shock and magnetopause (and therefore the size of the magnetosphere), has been shown to influence the intensity and morphology of the auroral radio and ultraviolet emissions, and transports energy and mass into the magnetosphere. Disentangling the Jovian, Io, and solar wind influences is critical in understanding the overall magnetospheric dynamics and especially the auroral morphology.
Multispectral observations of Jupiter's aurora
Advances in Space Research, 2000
Remote sensing of Jupiter's aurora from x-ray to radio wavelengths has revealed much about the nature of the jovian aurora and about the impact of ionosphere-magnetosphere coupling on the upper atmosphere of Jupiter. As indicated by the combination of x-ray and ultraviolet observations, both energetic heavy ions and electrons energized in the outer magnetosphere contribute to aurora1 excitation. Imaging with the Hubble Space Telescope in the ultraviolet and with the InfraRed Telescope Facility at infrared wavelengths shows several distinct regions of interaction: 1) a dusk sector where turbulent aurora1 patterns extend well into the polar cap; 2) a morning sector generally characterized by a single spatially confined aurora1 arc originating in the outer or middle magnetosphere of Jupiter; 3) diffuse emissions associated with the lo plasma -spectroscopy has provided important information about the thermal structure of Jupiter's aurora1 atmosphere and the altitude distribution of aurora1 particle energy deposition, while Lyman alpha line profiles yield clues to the nature of thermospheric dynamical effects. Galileo observations at visible wavelengths on the nightside offer a new view of the jovian aurora with unprecedented spatial information.
Geophysical Research Letters, 2017
We present the first comparison of Jupiter's auroral morphology with an extended, continuous, and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset, the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought. Plain Language Summary Jupiter's auroras (northern lights) are the brightest in the solar system, over a hundred times brighter than the Earth's. Auroras on Earth are driven by the solar wind, a million mile-per-hour stream of charged particles flowing away from the Sun, hitting the Earth's magnetic field, and stirring it around, but it is not known whether the solar wind causes any significant auroras on Jupiter. The main reason for this uncertainty is a lack of observations of the planet's auroras obtained while spacecraft have been near Jupiter and able to supply a full and continuous set of measurements of the solar wind and its accompanying magnetic field. In early mid-2016 Juno approached Jupiter, providing such an interplanetary data set, and we obtained over a month's worth of observations of Jupiter's auroras using the Hubble Space Telescope. We saw several solar wind storms, each causing auroral fireworks on Jupiter. We captured the most powerful auroras observed by Hubble to date, brightened main oval emissions, and flashing high-latitude patches of auroras during the solar wind storms. These results indicate that Jupiter's auroral response to the solar wind is more diverse than we previously have thought.