Magnetic Fields at Uranus

Ness, N. F.; Acuña, M. H.; Behannon, K. W.; Burlaga, L. F.; Connerney, J. E. P.; Lepping, R. P.; Neubauer, F. M.

doi:10.1126/science.233.4759.85

Cited by 372 publications

(244 citation statements)

References 38 publications

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“…Podolak et al (1990) suggested a stably stratified interior model instead. Nevertheless, a convective layer of a conducting material is needed to sustain a magnetic dynamo and to produce the quadrupolar fields observed for Uranus and Neptune (Ness et al 1986(Ness et al , 1989Connerney et al 1987Connerney et al , 1991. Water is assumed to be the dominant species in the layer where magnetic fields of ice giant planets are generated.…”

Section: Introductionmentioning

confidence: 99%

Miscibility Calculations for Water and Hydrogen in Giant Planets

Soubiran

Militzer

2015

ApJ

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We present results from ab initio simulations of liquid water-hydrogen mixtures in the range from 2 to 70 GPa and from 1000 to 6000 K, covering conditions in the interiors of ice giant planets and parts of the outer envelope of gas giant planets. In addition to computing the pressure and the internal energy, we derive the Gibbs free energy by performing a thermodynamic integration. For all conditions under consideration, our simulations predict hydrogen and water to mix in all proportions. The thermodynamic behavior of the mixture can be well described with an ideal mixing approximation. We suggest that a substantial fraction of water and hydrogen in giant planets may occur in homogeneously mixed form rather than in separate layers. The extentof mixing depends on the planet's interior dynamics and its conditions of formation, in particular on how much hydrogen was present when icy planetesimals were delivered. Based on our results, we do not predict water-hydrogen mixtures to phase separate during any stage of the evolution of giant planets. We also show that the hydrogen content of an exoplanet is much higher if the mixed interior is assumed.

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Section: Introductionmentioning

confidence: 99%

Miscibility Calculations for Water and Hydrogen in Giant Planets

Soubiran

Militzer

2015

ApJ

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“…As an illustrative example, we pick case 2 in (42b), when u>kz = 1-56172. Choosing the traveling wave speed V = 1, the traveling wave solutions of (51) show quasiperiodic behavior as shown in Fig. 14.…”

Section: Basic Equationsmentioning

confidence: 99%

Quasiperiodicity and chaos in the nonlinear evolution of the Kelvin-Helmholtz instability of supersonic anisotropic tangential velocity discontinuities

Choudhury¹,

Brown²

2003

Quart. Appl. Math.

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Abstract.A nonlinear stability analysis using a multiple-scales perturbation procedure is performed for the instability of two layers of immiscible, strongly anisotropic, magnetized, inviscid, arbitrarily compressible fluids in relative motion. Such configurations are of relevance in a variety of astrophysical and space configurations.For modes near the critical point of the linear neutral curve, the nonlinear evolution of the amplitude of the linear fields on the slow first-order scales is shown to be governed by a complicated nonlinear Klein-Gordon equation.The nonlinear coefficient turns out to be complex, which is, to the best of our knowledge, unlike previously considered cases and leads to completely different dynamics from that reported earlier. Both the spatially dependent and space-independent versions of this equation are considered to obtain the regimes of physical parameter space where the linearly unstable solutions either evolve to final permanent envelope wave patterns resembling the ensembles of interacting vortices observed empirically, or are disrupted via nonlinear modulation instability. In particular, the complex nonlinearity allows the existence of quasiperiodic and chaotic wave envelopes, unlike in earlier physical models governed by nonlinear Klein-Gordon equations. In addition, numerical diagnostics reveal the onset of chaos as a consequence of modulation of the external magnetic field.

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“…The complex magnetic field of these planets can be approximated to fairly good accuracy by a dipole field that is off-center and tilted (relative to the rotation axis) [Ness et al, 1986[Ness et al, , 1989. A first and preliminary magnetic field model for Neptune is Ness et al 's [1989] offset, tilted dipole (OTD) model, which is well suited for describing the overall largescale magnetic field and is useful for studying the magnetospheric plasma as a first approximation.…”

Section: Introductionmentioning

confidence: 99%

Contributions of the high‐degree multipoles of Neptune's magnetic field: An Euler potentials approach

Ho¹,

Huang²,

Gao³

1997

J. Geophys. Res.

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Abstract. A new technique of calculating the Euler potentials a and/3 based on the geometrical relations between the magnetic field structure and Euler potentials [Huang and Yu, 1995] was used to determine the a and/3 coordinates of Neptune's magnetic field. The result is a mathematical definable coordinate system for a field of which the nondipole terms are nonnegligible. A framework is thus established for future studying of plasma dynamics such as particle drifts and plasma convection. The magnetic field model used is the Goddard Space Flight Center/Bartol Research Institute's I8E1 model. The full I8E1 model was used to investigate the significance of the higher-degree multipoles beyond the octupole (up to the eighth degree in the spherical harmonic expansions), particularly near the planet's surface. The results were compared to those of the 08 model, which is a simplified version of the I8E1. We found that the higher-degree terms do not change significantly the overall results of the 08. However, on the planet's surface, footprints of inner drift shells fall into a few concentrated areas, opening more regions into which no particle from these drift shells can precipitate. Close examination of these "open" regions indicates that they are isolated magnetic field systems that may trap particles locally. Our results entail new interpretation of the Voyager 2 UV spectrometer measurements on the planet's nightside surface emissions. Particle precipitation emissions are found to be concentrated on the areas into which the drift shells collapse. These areas of high concentration of drift shell footprints and emissions indicate that the strong emissions are due to high particle downflux into these regions of high magnetic field intensity. Our results suggest that magnetic moments higher than the octupole may constitute nonnegligible components of the magnetic field of planets that have high nondipole terms, such as Neptune and Uranus. For Neptune the high-degree terms should be included for studying plasma processes within two planetary radii.

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Magnetic Fields at Uranus

Cited by 372 publications

References 38 publications

Miscibility Calculations for Water and Hydrogen in Giant Planets

Miscibility Calculations for Water and Hydrogen in Giant Planets

Quasiperiodicity and chaos in the nonlinear evolution of the Kelvin-Helmholtz instability of supersonic anisotropic tangential velocity discontinuities

Contributions of the high‐degree multipoles of Neptune's magnetic field: An Euler potentials approach

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