Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

Roussos, E.; Müller, Jakob; Simon, Sven; Bößwetter, A.; Motschmann, U.; Krupp, N.; Fränz, M.; Woch, J.; Khurana, K. K.; Dougherty, M. K.

doi:10.5194/angeo-26-619-2008

Cited by 54 publications

(84 citation statements)

References 43 publications

(64 reference statements)

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“…The first is that the properties of the plasma deposited on a moon's trailing hemisphere are uniform everywhere across this hemisphere. Simulations have shown that this is generally valid at least for Rhea [Roussos et al, 2008]. Farrell et al [2007], however, used equations by Samir et al [1983] suggesting that a density perturbation from the wake should propagate also upstream with the sonic speed, leading to a density (temperature) dropout (enhancement) even before the wake boundary.…”

Section: Validity Of the Assumptionsmentioning

confidence: 99%

“…It is also important that none of these models capture the electron dynamics in the wake, where some peculiar measurements are reported, such as extended depletions of very energetic electrons (>10 keV) or enhancements of 1-5 keV electrons in the wake center [Jones et al, 2008]. In addition, because of the low plasma speeds, the plasma distribution in the wake has a much different structure parallel to and perpendicular to the magnetic field [Roussos et al, 2008]. This requires that the wakeside hemisphere potentials be mapped in three dimensions.…”

Section: Application Of the Modelmentioning

confidence: 99%

“…Calculation of surface potentials in the leading hemisphere (wake) is also interesting but requires a model for the electron and ion distributions. While a series of analytical models and simulations can provide such an input [Samir et al, 1983;Farrell et al, 2007;Roussos et al, 2008;Simon et al, 2009], the results will probably be model dependent, and we want to avoid this at present. It is also important that none of these models capture the electron dynamics in the wake, where some peculiar measurements are reported, such as extended depletions of very energetic electrons (>10 keV) or enhancements of 1-5 keV electrons in the wake center [Jones et al, 2008].…”

Section: Application Of the Modelmentioning

confidence: 99%

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Surface charging of Saturn's plasma‐absorbing moons

et al. 2010

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[1] Recent results from the study of the interaction of Earth's moon with the solar wind have highlighted lunar surface charging as an important physical process not only for the local interaction of the surface and the impinging plasma but also for charged dust ejection and transport. Excluding Earth's moon, however, such studies have been limited to very few solar system bodies. Here we assess the importance of surface charging for the Saturnian plasma-absorbing moons. In this initial study, we focus on the various moons' trailing hemispheres and their variable charging patterns as a function of their magnetospheric local time. With only a few exceptions, our results indicate negative potentials for all moons, with the most extreme values predicted for Rhea. When the leading hemisphere is partially sunlit, the surface potential profile can be quite complex with many different transition regions. We also find that electrostatic acceleration of dust is at least equally as (if not more) important as it is for Earth's moon for the submicron grains, but it is probably not sufficient to explain the detection of the larger micron-sized grains in the vicinity of the large moons of the outer planets. Regarding Saturn's asteroid-sized moons, we predict that electrostatic forces can accelerate grains above the escape velocity and populate the Saturnian system and/or contribute to dust transport across those moons' surfaces. On the basis of these results, we also propose several methods by which Cassini's instruments could be used to directly observe the effects of surface charging.

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Section: Validity Of the Assumptionsmentioning

confidence: 99%

Section: Application Of the Modelmentioning

confidence: 99%

Section: Application Of the Modelmentioning

confidence: 99%

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Surface charging of Saturn's plasma‐absorbing moons

et al. 2010

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“…Rhea is an unmagnetised body and acts to absorb incident magnetodisk plasma [Khurana et al, 2008;Roussos et al, 2008]. Ionised material can be directly picked up by the motional electric field and form "pickup ion" current systems which, with the resulting j×B force and density gradients associated with the plasma wake [Simon et al, 2012;Khurana et al, 2017], slows down the incident magnetoplasma causing field-line draping and Alfvén wings.…”

Section: Introductionmentioning

confidence: 99%

Cassini CAPS Identification of Pickup Ion Compositions at Rhea

Desai

Taylor

Regoli

et al. 2018

Geophysical Research Letters

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Saturn's largest icy moon, Rhea, hosts a tenuous surface‐sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea and confirm that Cassini detected nongyrotropic fluxes of outflowing CO2+ during both the R1 and R1.5 encounters. Accounting for this nongyrotropy, we show that these possess comparable along‐track densities of ∼2 × 10−3 cm−3. Negatively charged pickup ions, also detected during R1, are surprisingly shown as consistent with mass 26 ± 3 u which we suggest are carbon‐based compounds, such as CN−, C2H−, C2−, or HCO−, sputtered from carbonaceous material on the moon's surface. The negative ions are calculated to possess along‐track densities of ∼5 × 10−4 cm−3 and are suggested to derive from exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO2 exosphere and surprisingly low O2 sputtering yields. These pickup ions provide important context for understanding the exospheric and surface ice composition of Rhea and of other icy moons which exhibit similar characteristics.

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“…Besides, the model has been successfully applied to the interaction between the Martian ionosphere and the solar wind (Simon et al, 2007a;Bößwetter et al, 2007), to cometary plasma interactions (Bagdonat and Motschmann, 2002;Motschmann and Kührt, 2006) and to the plasma environment of weakly magnetized asteroids (Simon et al, 2006a). Within the framework of the Cassini mission, the very weak magnetic field perturbations observed in the wakes of Saturn's icy satellites Tethys and Rhea have been successfully reproduced as well (Roussos et al, 2008;Simon et al, 2009b). Recently, a first application of our hybrid code to the plasma interaction of Enceladus has been presented at the AGU Fall Meeting (Kriegel et al, 2008;Kriegel, 2009).…”

Section: Model Description and Input Parametersmentioning

confidence: 90%

Real-time 3-D hybrid simulation of Titan's plasma interaction during a solar wind excursion

Simon

2009

Ann. Geophys.

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Abstract. The plasma environment of Saturn's largest satellite Titan is known to be highly variable. Since Titan's orbit is located within the outer magnetosphere of Saturn, the moon can leave the region dominated by the magnetic field of its parent body in times of high solar wind dynamic pressure and interact with the thermalized magnetosheath plasma or even with the unshocked solar wind. By applying a threedimensional hybrid simulation code (kinetic description of ions, fluid electrons), we study in real-time the transition that Titan's plasma environment undergoes when the moon leaves Saturn's magnetosphere and enters the supermagnetosonic solar wind. In the simulation, the transition between both plasma regimes is mimicked by a reversal of the magnetic field direction as well as a change in the composition and temperature of the impinging plasma flow. When the satellite enters the solar wind, the magnetic draping pattern in its vicinity is reconfigured due to reconnection, with the characteristic time scale of this process being determined by the convection of the field lines in the undisturbed plasma flow at the flanks of the interaction region. The build-up of a bow shock ahead of Titan takes place on a typical time scale of a few minutes as well. We also analyze the erosion of the newly formed shock front upstream of Titan that commences when the moon re-enters the submagnetosonic plasma regime of Saturn's magnetosphere. Although the model presented here is far from governing the full complexity of Titan's plasma interaction during a solar wind excursion, the simulation provides important insights into general plasma-physical processes associated with such a disruptive change of the upstream flow conditions. Keywords. Magnetospheric physics (Magnetosphere interactions with satellites and rings; Magnetosphere-ionosphere interactions) -Space plasma physics (Kinetic and MHD theory)

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Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

Cited by 54 publications

References 43 publications

Surface charging of Saturn's plasma‐absorbing moons

Surface charging of Saturn's plasma‐absorbing moons

Cassini CAPS Identification of Pickup Ion Compositions at Rhea

Real-time 3-D hybrid simulation of Titan's plasma interaction during a solar wind excursion

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