Excitation of the Ganymede Ultraviolet Aurora

Eviatar, A.; Strobel, D. F.; Wolven, B. C.; Feldman, P. D.; McGrath, M. A.; Williams, D. J.

doi:10.1086/321510

Cited by 58 publications

(117 citation statements)

References 31 publications

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“…We have inferred densities of 3 and 90 AMU cm −3 for G8 and G28 respectively from which we calculated an ionospheric scale height of 465 km, which is much smaller that the estimate of 1000 km by Gurnett et al (1996) but closer to the estimate of 600 km by Eviatar et al (2001a). Similarly, the plasma temperature obtained through the magnetospheric model by Eviatar et al (2001a) is 360 K, whereas Barth et al (1997) found a temperature of 450 K. The reason for this discrepancy of our values and previous estimates can be found in the location of Ganymede with respect to the Jovian current sheet. The calculations we performed did not take this into account.…”

Section: Discussionmentioning

confidence: 54%

“…Using these two different ambient plasma cases together to determine the ionospheric scale height will then lead to an underestimate when compared with the previous estimates. Gurnett et al (1996) and Eviatar et al (2001a) used the G1 and G2 flybys to obtain the scale height, with both flybys in similar ambient plasma conditions as G28.…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, plasma wave observations have shown typical magnetospheric emissions (Gurnett et al, 1996). Other aspects of Ganymede's magnetosphere include auroral emissions (Barth et al, 1997;Hall et al, 1998;Eviatar et al, 2001a) and the presence of polar caps (Khurana et al, 2007), high-latitude regions from which field lines emerge but do not return to Ganymede's surface.…”

Section: Introductionmentioning

confidence: 95%

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ULF waves in Ganymede's upstream magnetosphere

et al. 2013

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Abstract. Ganymede's mini-magnetosphere, embedded in Jupiter's larger one, sustains ULF (ultra-low frequency) waves that are analyzed here using data from two Galileo flybys that penetrate deeply into the upstream closed field line region. The magnetometer data are used to identify field line resonances, magnetopause waves and ion cyclotron waves. The plasma densities that are inferred from the interpretation of these waves are compared with the observations made by other plasma and wave experiments on Galileo and with numerical and theoretical models of Ganymede's magnetosphere.

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Section: Discussionmentioning

confidence: 54%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

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ULF waves in Ganymede's upstream magnetosphere

et al. 2013

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“…These images also show a background emission above the detection limit of 50 R but not exceeding 100 R across the rest of the disk of the satellite (Eviatar et al, 2001b). The oxygen emission is thought to be produced primarily by electron dissociative excitation of the molecular oxygen that dominates in Ganymede's tenuous atmosphere, although there is also likely a lesser contribution from electron excitation of the atomic oxygen component of the atmosphere.…”

Section: Introductionmentioning

confidence: 87%

“….) of its value at the surface at a radial distance of 1.005 R G (Eviatar et al, 2001b). The top of the atmosphere is assumed at 1.005 R G .…”

Section: Loss Cone At Ganymedementioning

confidence: 99%

The generation of Ganymede's diffuse aurora through pitch angle scattering

2017

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Abstract. Diffuse auroral intensities of neutral atomic oxygen OI λ1356 Å emission on Ganymede due to whistler mode waves are estimated. Pitch angle diffusion of magnetospheric electrons into the loss cone due to resonant wave-particle interaction of whistler mode waves is considered, and the resulting electron precipitation flux is calculated. The analytical yield spectrum approach is used for determining the energy deposition of electrons precipitating into the atmosphere of Ganymede. It is found that the intensities (4-30 R) calculated from the precipitation of magnetospheric electrons observed near Ganymede are inadequate to account for the observational intensities ( ≤ 100 R). This is in agreement with the conclusions reached in previous works. Some acceleration mechanism is required to energize the magnetospheric electrons. In the present work we consider the heating and acceleration of magnetospheric electrons by electrostatic waves. Two particle distribution functions (Maxwellian and kappa distribution) are used to simulate heating and acceleration of electrons. Precipitation of a Maxwellian distribution of electrons can produce about 70 R intensities of OI λ1356 Å emission for electron temperature of 150 eV. A kappa distribution can also yield a diffuse auroral intensity of similar magnitude for a characteristic energy of about 100 eV. The maximum contribution to the estimated intensity results from the dissociative excitation of O 2 . Contributions from the direct excitation of atomic oxygen and cascading in atomic oxygen are estimated to be only about 1 and 2 % of the total calculated intensity, respectively. The findings of this work are relevant for the present JUNO and future JUICE missions to Jupiter. These missions will provide new data on electron densities, electron temperature and whistler mode wave amplitudes in the magnetosphere of Jupiter near Ganymede.

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Consistent boundary conditions at nonconducting surfaces of planetary bodies: Applications in a new Ganymede MHD model

2014

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The interaction of planetary bodies with their surrounding magnetized plasma can often be described with the magnetohydrodynamic (MHD) equations, which are commonly solved by numerical models. For these models it is necessary to define physically correct boundary conditions for the plasma mass and energy density, the plasma velocity, and the magnetic field. Many planetary bodies have surfaces whose electrical conductivity is negligibly small and thus no electric current penetrates their surfaces. Magnetic boundary conditions, which consider that the associated radial electric current at the planetary surface is zero, are difficult to implement because they include the curl of the magnetic field. Here we derive new boundary conditions by a decomposition of the magnetic field in poloidal and toroidal parts. We find that the toroidal part of the magnetic field needs to vanish at the surface of the insulator. For the spherical harmonics coefficients of the poloidal part, we derive a Cauchy boundary condition, which also matches a possible intrinsic field by including its Gauss coefficients. Thus, we can additionally include planetary dynamo fields as well as time-variable induction fields within electrically conductive subsurface layers. We implement the nonconducting boundary condition in the MHD simulation code ZEUS-MP using spherical geometry and provide a numerical implementation in Fortran 90 as supporting information on the JGR website. We apply it to a model for Ganymede's plasma environment. Our model also includes a consistent set of boundary conditions for the other MHD variables density, velocity, and energy. With this model we can describe Galileo spacecraft observations in and around Ganymede's minimagnetosphere very well.

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Excitation of the Ganymede Ultraviolet Aurora

Cited by 58 publications

References 31 publications

ULF waves in Ganymede's upstream magnetosphere

ULF waves in Ganymede's upstream magnetosphere

The generation of Ganymede's diffuse aurora through pitch angle scattering

Consistent boundary conditions at nonconducting surfaces of planetary bodies: Applications in a new Ganymede MHD model

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