Mapping of coma anisotropies to plasma structures of weak comets: a 3-D hybrid simulation study

Gortsas, Nikolaos; Motschmann, U.; Kührt, Ekkehard; Knollenberg, J.; Simon, Sven; Boesswetter, A.

doi:10.5194/angeo-27-1555-2009

Cited by 14 publications

(8 citation statements)

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“…25 This meant that even at large heliocentric distances the 26 weakly outgassing nucleus of 67P mass-loads the solar 27 wind plasma [5,6]. 28 29 Various ionization processes, such as electron-impact 30 ionization, photo-ionization, and charge exchange, 31 contribute to the shape of the near-cometary environ-32 ment [16][17][18]. Rosetta observed a radial dependence of Illustration of the solar wind interaction with a weakly outgassing comet representative of 67P/Churyumov-Gerasimenko at a heliocentric distance of 4.0 − 4.5 AU.…”

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Building a Weakly Outgassing Comet from a Generalized Ohm’s Law

et al. 2019

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When a weakly outgassing comet is sufficiently close to the Sun, the formation of an ionized coma results in solar wind mass loading and magnetic field draping around its nucleus. Using a 3D fully kinetic approach, we distill the components of a generalized Ohm's law and the effective electron equation of state directly from the self-consistently simulated electron dynamics and identify the driving physics in the various regions of the cometary plasma environment. Using the example of space plasmas, in particular multi-species cometary plasmas, we show how the description for the complex kinetic electron dynamics can be simplified through a simple effective closure, and identify where an isotropic single-electron fluid Ohm's law approximation can be used, and where it fails.Numerical models that seek to describe the evolution 1 of plasma without self-consistently including the electron 2 dynamics, such as (multi-)fluid and hybrid simulation 3 approaches [1], need to rely on a relation that prescribes 4 the behavior of the unresolved species. Typically a 5 generalized Ohm's law (GOL) is assumed [2], combined 6 with a closure relation such as a polytropic or a double 7 adiabatic evolution [3,4]. In this letter, we show how a 8 GOL can unravel the hidden mysteries of multi-species 9 plasma environments, such as the solar wind plasma 10 interaction with a weakly outgassing comet [5][6][7]. We 11 indicate where reduced plasma models can be applied, 12 e.g., to gain more direct access to the ongoing physics 13 and/or to decrease the needed amount of computational 14 resources, and show the consequences of this compromise. 15 * mailto: jandeca@gmail.com 16 The Rosetta spacecraft caught up with comet 17 67P/Churyumov-Gerasimenko (hereafter 67P) at a 18 heliocentric distance of 3.6 AU [8, 9]. At a few hundreds 19 of kilometers from the cometary nucleus, the Rosetta 20 plasma instruments, quite unexpectedly, picked up 21 the signatures of a plasma environment dominated 22 the plasma density with distance from the nucleus [19, 20] 34 or, in other words, there exists a continuously changing 35 ratio between the cometary and the upstream solar wind 36 plasma density throughout 67P's plasma environment, 37 both along the Sun-comet direction as well as in the 38 meridian plane [21-23]. To first order, for a weakly 39 outgassing comet, the dynamical interaction that de-40 termines the general structure of the cometary plasma 41 environment is representative of a four-fluid coupled 42 system (illustrated in Fig. 1), where the solar wind 43 electrons move to neutralize the cometary ions and the 44 cometary electrons organize themselves to neutralize the 45 solar wind ions [7]. 46 47 In addition to a detailed understanding of the kinetic 48 dynamics that governs the solar wind interaction with 49 a weakly outgassing comet, in this letter we provide 50 feedback to (multi-)fluid [24-29] and hybrid [16, 30-37] 51 models where the electrons dynamics is prescribed 52 through a GOL combined with an electron closure 53 relation. Using a f...

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Building a Weakly Outgassing Comet from a Generalized Ohm’s Law

et al. 2019

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“…Up to date, the focus of modelling studies to predict 28 and explain the complex cometary plasma observations 29 has been on MHD/multi-fluid [14][15][16][17][18][19] and hybrid (using 30 a kinetic description for the ions but describing the 31 electrons as a mass-less fluid) [20][21][22][23][24][25][26] simulations, 32 leading to comprehensive models for the ion dynamics.…”

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Electron and Ion Dynamics of the Solar Wind Interaction with a Weakly Outgassing Comet

et al. 2017

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“…The dynamics of the solar wind protons and the cometary ions are described in the framework of the macroparticle approach while the electrons are treated as a massless, charge-neutralizing fluid. The key features of the hybrid model are discussed in preceding publications Gortsas et al 2009). Therefore, only a brief overview of the main aspects for this study shall be given.…”

Section: Simulation Model and Input Parametersmentioning

confidence: 99%

“…Prialnik et al (2004) and the reference therein. Previous articles concerning the plasma environment of comets were performed at some fixed heliocentric distances and the outgassing strength was set to an estimated number based on observations, or else it was derived from a simple outgassing model (Lipatov et al 2002;Motschmann & Kührt 2006;Delamere 2006;Gortsas et al 2009). One of the first studies of the dynamic and very complex phenomenon of a comet approaching the Sun and thereby gaining strength in its outgassing of volatile materials has been presented by .…”

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Global plasma-parameter simulation of Comet 67P/Churyumov-Gerasimenko approaching the Sun

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Kührt

et al. 2010

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We simulate the evolution of the plasma environment of comet 67P/Churyumov-Gerasimenko (CG), which is the target comet of the European Space Agency's (ESA) Rosetta mission, as the comet approaches the Sun. The plasma environment is calculated in three dimensions with a hybrid plasma model. The model treats the dynamics of the solar wind protons and the cometary ions in the framework of the macroparticle approach while the electrons are treated as a massless, charge-neutralizing fluid. The simulation starts at 4.2 AU and finishes at 1.3 AU. The outgassing strength of the comet is calculated from a thermal nucleus model. The model accounts for heat conduction, heat advection, gas diffusion, sublimation, and condensation processes in a porous ice-dust matrix with moving boundaries. The movement of the boundaries (Stefan problem) is accounted for by a temperature remapping technique. The maxima of the cometary ion flux and of the magnetic field in the simulation domain are presented as functions of heliocentric distance. The bow shock (BS), the ion composition boundary (ICB), and the magnetic pileup boundary (MPB) position along the Sun-comet line as a function of heliocentric distance are also discussed. A comparison of the BS position with an analytical formula yields good agreement. The MPB and the ICB along the Sun-comet line coincide.

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Mapping of coma anisotropies to plasma structures of weak comets: a 3-D hybrid simulation study

Cited by 14 publications

References 26 publications

Building a Weakly Outgassing Comet from a Generalized Ohm’s Law

Building a Weakly Outgassing Comet from a Generalized Ohm’s Law

Electron and Ion Dynamics of the Solar Wind Interaction with a Weakly Outgassing Comet

Global plasma-parameter simulation of Comet 67P/Churyumov-Gerasimenko approaching the Sun

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