Io Jupiter interaction, millisecond bursts and field-aligned potentials
TL;DR: In this paper, the authors performed an automated analysis of 230 high-resolution dynamic spectra of S-bursts, providing 5 × 10 6 frequency drift measurements and confirmed over a large number of measurements that the frequency drift d f / d t (f ) is in average negative and decreases (in absolute value) at high frequencies, as predicted by the adiabatic theory.
About: This article is published in Planetary and Space Science.The article was published on 2007-01-01. It has received 61 citations till now. The article focuses on the topics: Jupiter & Jovian.
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TL;DR: The electron-cyclotron maser is a process that generates coherent radiation from plasma as mentioned in this paper, and it has gained increasing attention as a dominant mechanism of producing high-power radiation in natural high-temperature magnetized plasmas.
Abstract: The electron–cyclotron maser is a process that generates coherent radiation from plasma. In the last two decades, it has gained increasing attention as a dominant mechanism of producing high-power radiation in natural high-temperature magnetized plasmas. Originally proposed as a somewhat exotic idea and subsequently applied to include non-relativistic plasmas, the electron–cyclotron maser was considered as an alternative to turbulent though coherent wave–wave interaction which results in radio emission. However, when it was recognized that weak relativistic corrections had to be taken into account in the radiation process, the importance of the electron–cyclotron maser rose to the recognition it deserves. Here we review the theory and application of the electron–cyclotron maser to the directly accessible plasmas in our immediate terrestrial and planetary environments. In situ access to the radiating plasmas has turned out to be crucial in identifying the conditions under which the electron–cyclotron maser mechanism is working. Under extreme astrophysical conditions, radiation from plasmas may provide a major energy loss; however, for generating the powerful radiation in which the electron–cyclotron maser mechanism is capable, the plasma must be in a state where release of susceptible amounts of energy in the form of radiation is favorable. Such conditions are realized when the plasma is unable to digest the available free energy that is imposed from outside and stored in its particle distribution. The lack of dissipative processes is a common property of collisionless plasmas. When, in addition, the plasma density becomes so low that the amount of free energy per particle is large, direct emission becomes favorable. This can be expressed as negative absorption of the plasma which, like in conventional masers, leads to coherent emission even though no quantum correlations are involved. The physical basis of this formal analogy between a quantum maser and the electron–cyclotron maser is that in the electron–cyclotron maser the free-space radiation modes can be amplified directly. Several models have been proposed for such a process. The most famous one is the so-called loss-cone maser. However, as argued in this review, the loss-cone maser is rather inefficient. Available in situ measurements indicate that the loss-cone maser plays only a minor role. Instead, the main source for any strong electron–cyclotron maser is found in the presence of a magnetic-field-aligned electric potential drop which has several effects: (1) it dilutes the local plasma to such an extent that the plasma enters the regime in which the electron–cyclotron maser becomes effective; (2) it generates energetic relativistic electron beams and field-aligned currents; (3) it deforms, together with the magnetic mirror force, the electron distribution function, thereby mimicking a high energy level sufficiently far above the Maxwellian ground state of an equilibrium plasma; (4) it favors emission in the free-space RX mode in a direction roughly perpendicular to the ambient magnetic field; (5) this emission is the most intense, since it implies the coherent resonant contribution of a maximum number of electrons in the distribution function to the radiation (i.e., to the generation of negative absorption); (6) it generates a large number of electron holes via the two-stream instability, and ion holes via the current-driven ion-acoustic instability which manifest themselves as subtle fine structures moving across the radiation spectrum and being typical for the electron–cyclotron maser emission process. These fine structures can thus be taken as the ultimate identifier of the electron–cyclotron maser. The auroral kilometric radiation of Earth is taken here as the paradigm for other manifestations of intense radio emissions such as the radiation from other planets in the solar system, from exoplanets, the Sun and other astrophysical objects.
358 citations
Cites background from "Io Jupiter interaction, millisecond..."
...Recently, Zarka et al. (2005) argued that S-bursts are the result of loss-cone maser activity inside the Io flux tube....
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...…extrasolar planets has immediately stimulated the idea that in analogy to the strongly magnetized planets in the solar system, exoplanets could also radiate in the radio band, possibly emitting maser radiation (Farrell et al. 1999; Bastian et al. 2000; Zarka et al. 2001b; Winterhalter et al. 2005)....
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...Application to Jupiter and radiation from the other magnetized planets followed, and speculations about radiation emitted from extrasolar planets when they are magnetized strongly enough have been published as well (Bastian et al. 2000; Zarka et al. 2001a,b)....
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...Searches have been going on at the Very Large Array (VLA) in New Mexico (Bastian et al. 2000) and a comparable array UTR-2 in Kharkov (Ukraine) (Zarka et al. 2001b)....
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...From the knowledge of the emissivities of Earth and Jupiter under solar-wind conditions, one may scale emissivities up to exoplanets of the family of ‘hot Jupiters’ close to their mother stars (Zarka et al. 2001b)....
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University of Colorado Boulder1, INAF2, Southwest Research Institute3, University of Texas at San Antonio4, University of Liège5, University of Leicester6, Goddard Space Flight Center7, Planetary Science Institute8, University of Iowa9, Jet Propulsion Laboratory10, Johns Hopkins University11, University of California, Los Angeles12, Centre national de la recherche scientifique13
TL;DR: Junior as discussed by the authors is the first spacecraft to enter polar orbit of Jupiter and venture deep into unexplored polar territories of the magnetosphere, where it carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter's radiation belts.
Abstract: In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and venture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we review current understanding of the structure and dynamics of the magnetosphere and summarize the outstanding issues. The Juno mission profile involves (a) a several-week approach from the dawn side of Jupiter’s magnetosphere, with an orbit-insertion maneuver on July 6, 2016; (b) a 107-day capture orbit, also on the dawn flank; and (c) a series of thirty 11-day science orbits with the spacecraft flying over Jupiter’s poles and ducking under the radiation belts. We show how Juno’s view of the magnetosphere evolves over the year of science orbits. The Juno spacecraft carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter’s radiation belts. We summarize how these Juno measurements address issues of auroral processes, microphysical plasma physics, ionosphere-magnetosphere and satellite-magnetosphere coupling, sources and sinks of plasma, the radiation belts, and the dynamics of the outer magnetosphere. To reach Jupiter, the Juno spacecraft passed close to the Earth on October 9, 2013, gaining the necessary energy to get to Jupiter. The Earth flyby provided an opportunity to test Juno’s instrumentation as well as take scientific data in the terrestrial magnetosphere, in conjunction with ground-based and Earth-orbiting assets.
192 citations
TL;DR: In this paper, it was shown that the Alfven waves need to be filamented by a turbulent cascade process and accelerate the electrons at high latitude in order to explain the observations and to form a consistent scheme of the Io-Jupiter interaction.
Abstract: [1] Io's motion relative to the Jovian magnetic field generates a power of about 1012 W, which is thought to propagate as an Alfven wave along the magnetic field line. This power is transmitted to the electrons, which will then precipitate and generate the observed auroral phenomena from UV to radio wavelengths. A more detailed look at this hypothesis shows some difficulties: Can the Alfven waves escape the torus or are they trapped inside? Where and how are the particles accelerated? In which direction? Is there enough power transmitted to the particles to explain the strong brightness of the auroral emissions in UV, IR, visible, and radio? In other words, can we make a global, consistent model of the Io-Jupiter interaction that matches all the observations? To answer these questions, we review the models and studies that have been proposed so far. We show that the Alfven waves need to be filamented by a turbulent cascade process and accelerate the electrons at high latitude in order to explain the observations and to form a consistent scheme of the Io-Jupiter interaction.
98 citations
TL;DR: In this article, the ionospheric response to auroral precipitation at the giant planets is reviewed, using models and observations The emission processes for aurorae at radio, infrared, visible, ultraviolet, and X-ray wavelengths are described, and exemplified using ground-and space-based observations Comparisons between the emissions at different wavelengths are made, where possible, and interpreted in terms of precipitating particle characteristics or atmospheric conditions.
Abstract: The ionospheric response to auroral precipitation at the giant planets is reviewed, using models and observations The emission processes for aurorae at radio, infrared, visible, ultraviolet, and X-ray wavelengths are described, and exemplified using ground- and space-based observations Comparisons between the emissions at different wavelengths are made, where possible, and interpreted in terms of precipitating particle characteristics or atmospheric conditions Finally, the spatial distributions and dynamics of the various components of the aurorae (moon footprints, low-latitude, main oval, polar) are related to magnetospheric processes and boundaries, using theory, in situ, and remote observations, with the aim of distinguishing between those related to internally-driven dynamics, and those related to the solar wind interaction
95 citations
TL;DR: In this article, a good fit of arcs t-f location and shape is obtained for loss-cone driven (oblique) emission beamed in a hollow cone of half-angle ≥ 80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤ 1°.
Abstract: [1] The electrodynamic interaction between Io and Jupiter causes electron acceleration in/near the Io flux tube (IFT), which in turn produces intense radio emissions in the hecto-decameter range, displaying arc shapes in the time-frequency plane. The shapes depend on the hemisphere of origin of the emission and on the Io-Jupiter-observer geometry. Assuming radio wave generation by the cyclotron-maser instability, we simulate t-f arc shapes as a function of emission beaming, lead angle between the radio emitting field line and the instantaneous Io field line, and electron energy. A good fit of arcs t-f location and shape is obtained for loss-cone driven (oblique) emission beamed in a hollow cone of half-angle ≥80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤1°. The lead angle is found between a few degrees and ∼40° in both hemispheres. Resonant electron energies are about a few keV. Implications on the absence of a plasma cavity at IFT footprints and on Jupiter's internal magnetic field model are discussed.
73 citations
References
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01 Jan 2004
TL;DR: Io's plasma interaction with its torus is an exceptionally interesting case of magnetospheric plasma flowing past a body with a tenuous atmosphere as discussed by the authors, and major progress in our understanding of Io's interaction has occurred in the last 10 years based on the rich data sets acquired by the Galileo spacecraft in orbit around Jupiter with seven close flybys of Io supplemented by Earth-based remote-sensing observations of unprecedented resolution.
Abstract: Io’s plasma interaction with its torus is an exceptionally interesting case of magnetospheric plasma flowing past a body with a tenuous atmosphere. Major progress in our understanding of Io’s interaction has occurred in the last 10 years based on the rich data sets acquired by the Galileo spacecraft in orbit around Jupiter with seven close flybys of Io supplemented by Earth-based remote-sensing observations of unprecedented resolution. This system, i.e, Io and its atmosphere, the Io plasma torus, and Jupiter with its magnetosphere, is very strongly coupled with a number of feedback mechanisms. In the history of space science, this system has also played an important role in the progress of understanding satellite plasma interactions in general.
97 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...Observer–planet–satellite angle) (Carr et al., 1983) and are due to the Io–Jupiter interaction (Queinnec and Zarka, 1998; Saur et al., 2004 )....
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TL;DR: In this paper, a study of the temporal evolution of the interaction of Alfven waves (AW) with a plasma inhomogeneous in a direction transverse to the static magnetic field is presented.
Abstract: . Investigating the process of electron acceleration in auroral regions, we present a study of the temporal evolution of the interaction of Alfven waves (AW) with a plasma inhomogeneous in a direction transverse to the static magnetic field. This type of inhomogeneity is typical of the density cavities extended along the magnetic field in auroral acceleration regions. We use self-consistent Particle In Cell (PIC) simulations which are able to reproduce the full nonlinear evolution of the electromagnetic waves, as well as the trajectories of ions and electrons in phase space. Physical processes are studied down to the ion Larmor radius and electron skin depth scales. We show that the AW propagation on sharp density gradients leads to the formation of a significant parallel (to the magnetic field) electric field (E-field). It results from an electric charge separation generated on the density gradients by the polarization drift associated with the time varying AW E-field. Its amplitude may reach a few percents of the AW E-field. This parallel component accelerates electrons up to keV energies over a distance of a few hundred Debye lengths, and induces the formation of electron beams. These beams trigger electrostatic plasma instabilities which evolve toward the formation of nonlinear electrostatic structures (identified as electron holes and double layers). When the electrostatic turbulence is fully developed we show that it reduces the further wave/particle exchange. This sequence of mechanisms is analyzed with the program WHAMP, to identify the instabilities at work and wavelet analysis techniques are used to characterize the regime of energy conversions (from electromagnetic to electrostatic structures, from large to small length scales). This study elucidates a possible scenario to account for the particle acceleration and the wave dissipation in inhomogeneous plasmas. It would consist of successive phases of acceleration along the magnetic field, the development of an electrostatic turbulence, the thermalization and the heating of the plasma. Space plasma physics (charged particle motion and acceleration; numerical studies).
95 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...The acceleration may be due, for instance, to small-scale Alfvén waves (Génot et al., 2004) encountering plasma density gradients, or to larger scale trapped Alfvén waves (Lysak and Song, 2003)....
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TL;DR: In this paper, the authors investigated the downstream electron acceleration using one-dimensional spatial, two-dimensional velocity static Vlasov solutions under the constraint of quasi-neutrality and an applied potential drop, and found that localized electric potential drops tend to form at 1.5-2.5 Rj Jovicentric distance.
Abstract: [1] Recent observations of auroral arcs on Jupiter suggest that electrons are being accelerated downstream from Io's magnetic footprint, creating detectable emissions. The downstream electron acceleration is investigated using one-dimensional spatial, two-dimensional velocity static Vlasov solutions under the constraint of quasi-neutrality and an applied potential drop. The code determines self-consistent charged particle distributions and potential structure along a magnetic field flux tube in the upward (with respect to Jupiter) current region of Io's wake. The boundaries of the flux tube are the Io torus on one end and Jupiter's ionosphere on the other. The results indicate that localized electric potential drops tend to form at 1.5-2.5 Rj Jovicentric distance. A sufficiently high secondary electron density causes an auroral cavity to be produced similar to that on Earth. Interestingly, the model results suggest that the proton and the hot electron population in the Io torus control the electron current densities between the Io torus and Jupiter and thus may control the energy flux and the brightness of the aurora downstream from Io's magnetic footprint. The parallel electric fields also are expected to create an unstable horseshoe electron distribution inside the auroral cavity, which may lead to the shell electron cyclotron maser instability. Results from our model suggest that in spite of the differing boundary conditions and the large centrifugal potentials at Jupiter, the auroral cavity formation may be similar to that of the Earth and that parallel electric fields may be the source mechanism of Io-controlled decametric radio emissions.
74 citations
TL;DR: In this article, an automated analysis of an extensive set of digital radio observations at very high temporal and spectral resolutions is presented, which strongly suggests that S-bursts are the cyclotron-maser emission of electron populations with ∼5 keV energy, accelerated near Io and then in quasi-adiabatic motion along magnetic field lines connecting the Io torus to Jupiter's auroral regions.
Abstract: Jovian S-bursts are intense impulsive decameter radio spikes drifting in frequency in tens of milliseconds over several hundreds of kHz up to a few MHz. Their generation scenario has been much debated for 30 years. The automated analysis of an extensive set of digital radio observations at very high temporal and spectral resolutions is presented here. It strongly suggests that S-bursts are the cyclotron-maser emission of electron populations with ∼5 keV energy, accelerated near Io and then in quasi-adiabatic motion along magnetic field lines connecting the Io torus to Jupiter's auroral regions. This scenario is consistent with Voyager observations of Alfven waves near Io's wake and with recent infrared observations of the Io flux tube footprint. The total energy, velocity and pitch angle of the radiating electrons, and the extent of the bursts radiosources are deduced from the radio measurements, which appear as a promising remote sensing tool for the Jovian magnetosphere, and possibly that of other “radio” planets.
71 citations
"Io Jupiter interaction, millisecond..." refers background or methods or result in this paper
...An automatic S-bursts recognition, identification and parallel energy calculation allowed us to confirm, with 5 10 measurements, the decrease of the drift at frequencies above 30MHz, as first seen by Zarka et al. (1996). We confirm thus the average adiabatic motion of the electrons emitting the Jovian S-bursts with an energy of 4:5 1:1 keV....
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...In previous papers (Zarka et al., 1996; Galopeau et al., 1999), drifts were studied and represented by the drift rate as a function of the frequency ðdf =dtÞðf Þ, and then compared to the drift rate ðdf =dtÞðf ceÞ predicted by the adiabatic model....
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...Zarka et al. (1996) introduced a dipolar magnetic field model with a moment equal to 7G:RJ ....
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...3a shows the drift rates measurements made by Zarka et al. (1996) and before (see references therein)....
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...Solid dots present the measurements made by Zarka et al. (1996) and open ones measurement made in previous papers....
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TL;DR: In this article, the authors developed an equation for Io's electric field/electric potential which includes Io's inhomogeneous and anisotropic conductances and treated Io's far-field interaction in both limits: the unipolar inductor and the Alfven wing models.
Abstract: [1] In this paper we develop an equation for Io's electric field/electric potential which includes Io's inhomogeneous and anisotropic conductances and treats Io's far-field interaction in both limits: the unipolar inductor and the Alfven wing models. We solve this equation for constant conductances within an elliptically shaped Ionian ionosphere, which leads to useful analytic expressions for properties of Io's local interaction, specifically, the total electric current driven by Io's interaction. Several previous calculations underestimated the total electric current by a factor of two. Oversimplifications of the Alfvenic current system might be one of the reasons. Our expressions also show that it is not the voltage across Io's ionosphere, as often assumed, that is physically related to the electric current; but it is the electric field and the extensions of the ionosphere in both directions. We show in addition that the Alfvenic and unipolar inductor models lead to different properties of Io's local interaction, e.g., the maximum plasma speed up around Io is higher in the Alfvenic coupling case.
51 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...This electric field induces currents and/or Alfvén waves (Goldreich and Lynden-Bell, 1969; Neubauer, 1980; Saur, 2004) which accelerate electrons from the Io torus toward Jupiter along the magnetic field...
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...As the Io–Jupiter plasma has the structure of an Alfvén wing (Neubauer, 1980; Saur, 2004), we can expect that Alfvén waves play an important role in the acceleration of the electrons....
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