Dynamic Martian magnetosphere: Transient twist induced by a rotation of the IMF

International audienceSimulation studies of the Martian environment are usually restricted to stationary situations under various steady conditions of the solar wind and solar radiation. Dynamic transients and their implications have so far attracted little attention although global simulation models can provide valuable insights to understand disagreements between simulations and in situ observations. We make use of a three dimensional multispecies hybrid simulation model to investigate the response of the Martian plasma environment to a sudden rotation of the IMF. The simulation model couples charged and neutral species via three ionisation mechanisms: the absorption of solar extreme ultraviolet radiation, the impact of solar wind electrons, and the charge exchange between ions and neutral atoms. When a rotational discontinuity conveyed by the solar wind reaches the Martian environment the bow shock adapts quickly to the new solar wind conditions in contrast to the induced magnetosphere, especially the magnetic lobes in the wake. Timescales necessary to recover a stationary state can be estimated from such simulations and have some implications for space observations especially in the use of magnetic field proxies and for organizing particle measurements made by a spacecraft like Mars Express without an onboard magnetometer

Hybrid multi-grids simulations of Ganymede's magnetosphere

International audienceThe Jovian satellite Ganymede is the biggest moon of our solar system. One of the main motivation of our interest for this moon is its own intrinsic magnetic field, which has been discovered during the Galileo mission (Kivelson et al. 1996). The magnetic field of Ganymede directly interacts with the corotating jovian plasma, leading to the formation of a mini-magnetosphere which is embedded in the giant magnetosphere of Jupiter. This is the only known case of interaction between two planetary magnetospheres.In the frame of the European space mission JUICE (Jupiter Icy moon Exploration), we investigate this unique interaction with a 3D parallel multi-species hybrid model. This model is based on the CAM-CL algorithm (Matthews 1994) and has been used to study the ionized environments of Titan, Mars and Mercury. In the hybrid formalism, ions are kinetically treated whereas electrons are considered as a zero-inertial fluid to ensure the quasi-neutrality of the plasma. The temporal evolution of the electromagnetic fields is calculated solving Maxwell's equations. The jovian magnetospheric plasma is described as being composed of oxygen and proton ions. The magnetic field of Ganymede, which includes dipolar and induced components (Kivelson et al, 2002), is distorted by its interaction with the Jovian plasma and formed the Alfvén wings. The planetary plasma is described as being composed of O+, with a scale height equal to 125 km. The description of the exosphere is provided by the 3D multi-species collisional exospheric/atmospheric model of Leblanc et al, (2015) and Turc et al. (2014). The ionization of this neutral exosphere by charge exchanges, by electronic impacts, and by reaction with solar photons contributes to the production of planetary plasma. In this model, calculations are performed on a cartesian simulation grid which is refined (down to ~120 km of spatial resolution) at Ganymede, using a multi-grids approach (Leclercq et al., submitted, 2015). Results are compared with Galileo observations obtained during the G1, G2 and G8 flybys

Ionization processes in the atmosphere of Titan. II. Electron precipitation along magnetic field lines

International audienceThe Cassini probe regularly passes the vicinity of Titan, providing new insights into particle precipitation by use of its electron and ion spectrometers. A discrepancy between precipitation models and observations of electron fluxes has been found. This discrepancy was suspected to be caused by the geometry of the magnetic field. Aims. In this article, we compute the electron impact ionization in the nightside ionosphere of Titan, assuming non-trivial geometry for the magnetic field lines. Methods. We use the TransTitan model, modified to take into account the magnetic field line geometry in the nightside, and we compare these results with the electron flux measurements during the T5 fly-by of Cassini. We use several magnetic field line geometries, including one produced by hybrid simulations. Results. The geometry of the lines implies a longer path of the electron inside the atmosphere of Titan. The electron fluxes are therefore modified considerably compared to the vertical precipitation hypothesis. At an altitude of 1200 km, the electron flux can be divided up to ten times with a field line resulting from hybrid simulation. Thanks to the use of more accurate field lines, the model reproduces the experiment well without any further adjustment of the precipitated measured electron flux. Conclusions. Several hypothesis had been suggested to explain the discrepancies between the different models and the observation of the electron flux during the T5 fly-by of Cassini. Our approach shows that the most probable explanation is the magnetic field line geometry. This work shows that the computation of ion production by electron impact in the atmosphere of Titan needs the consideration of both magnetic field and the input electron fluxes. Based on these considerations, our model can compute the conditions for future fly-by, and could be used to compare models with experiments

Solar wind charge exchange X-ray emission from Mars Model and data comparison

Aims. We study the soft X-ray emission induced by charge exchange (CX) collisions between solar-wind, highly charged ions and neutral atoms of the Martian exosphere. Methods. A 3D multi species hybrid simulation model with improved spatial resolution (130 km) is used to describe the interaction between the solar wind and the Martian neutrals. We calculated velocity and density distributions of the solar wind plasma in the Martian environment with realistic planetary ions description, using spherically symmetric exospheric H and O profiles. Following that, a 3D test-particle model was developed to compute the X-ray emission produced by CX collisions between neutrals and solar wind minor ions. The model results are compared to XMM-Newton observations of Mars. Results. We calculate projected X-ray emission maps for the XMM-Newton observing conditions and demonstrate how the X-ray emission reflects the Martian electromagnetic structure in accordance with the observed X-ray images. Our maps confirm that X-ray images are a powerful tool for the study of solar wind - planetary interfaces. However, the simulation results reveal several quantitative discrepancies compared to the observations. Typical solar wind and neutral coronae conditions corresponding to the 2003 observation period of Mars cannot reproduce the high luminosity or the corresponding very extended halo observed with XMM-Newton. Potential explanations of these discrepancies are discussed.Comment: 10 pages, 5 figures, accepted for publication in Astron. Astrophysic

A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation

International audienceThe interaction of the solar wind (SW) with the magnetic field of Mercury is investigated by means of a three dimensional parallelized multispecies hybrid model. A comparison between two mathematical representations of Mercury's intrinsic magnetic field is studied. The first model is an Offset Dipole (OD) having the offset and dipolar moment reported by Anderson et al. (2011). The second model is a combination of a Dipole and a Quadrupole (DQ), the total field is fitted to the offset dipolar field, for northern latitudes greater than 50°. Simulations reproduce the features which characterize Mercury's interaction with the SW, encompassing the Bow Shock (BS), the magnetosheath, the magnetotail, the "cusps" region and the neutral current sheet. Global hybrid simulations of the Hermean magnetosphere run for the OD and DQ models demonstrate that the southern parts of the magnetospheres produced by the OD and DQ models differ greatly in topology and volume meanwhile their northern parts-are quite similar. In particular the DQ model exhibits a dome of closed field lines around the south pole in contrast to the OD. Without further information on the intrinsic magnetic field of the planet in the southern region which should be provided by BepiColombo after year 2020, we can only speculate on the influence of the different magnetic topologies on the magnetospheric dynamics

A global hybrid model for Titan's interaction with the Kronian plasma: Application to the Cassini Ta flyby

International audienceThe interaction between the corotating magnetospheric plasma of Saturn and the exosphere of Titan is investigated by means of a three-dimensional and multispecies hybrid simulation model coupling charged and neutral species via three ionizing mechanisms: the absorption of extreme ultraviolet solar photons, the impacts of magnetospheric electrons, and the charge exchange reactions between ions and neutral atoms or molecules. The simulation model includes the low and energetic components of the magnetospheric plasma, the main exospheric neutral species (molecular hydrogen and nitrogen and methane), and the atmospheric slowing down of charged particles penetrating below the exobase. Ionization rates of the exospheric species are computed as consistently as possible for each of the three ionizing mechanisms by making use of the relevant local number densities and cross sections or ionization frequencies. This model is thus able to provide a priori estimates of the escaping fluxes of exospheric ionic species and to separate for the contributions of the different ionization sources. A simulation run has been made for the conditions encountered by spacecraft Cassini during flyby Ta of Titan on 26 October 2004. Results are presented to characterize the main features of the simulated plasma environment of Titan: the induced magnetic tail and the flow of magnetospheric plasma around Titan, as well as the wake and the acceleration of the planetary plasma. Considering the coarse spatial resolution of the present simulation, these features are in reasonable agreement with in situ plasma measurements made by spacecraft Cassini

Modélisation de l'interaction du vent solaire, ou du plasma Kronien, avec les environnements neutres de Mars et de Titan

Le champ magnétique de Mars est trop faible et trop lacunaire pour empêcher le vent solaire de s'approcher de l'atmosphère de la planète. L'exosphère, la partie haute de l'atmosphère, se trouve donc partiellement ionisée par les photons solaires, par les électrons du vent solaire et par les réactions d'échanges de charge entre les protons du vent solaire et les atomes neutres planétaires qui produisent des ions planétaires de faible énergie et des atomes neutres énergétiques (acronyme anglais ENA), modifiant ainsi la composition du plasma au voisinage de la planète. Ces processus affectent l'écoulement du vent du solaire auquel ils prennent de l'énergie et de la quantité de mouvement pour accélérer les ions nouvellement créés tout en augmentant la masse volumique du vent solaire. L'interaction entre le vent solaire et l'exosphère de Mars est suffisamment forte pour modifier l'échappement atmosphérique des constituants les plus légers et peut ainsi influer sur l'évolution chimique de l'atmosphère, en particulier sur son contenu en eau. Titan, le plus gros satellite de Saturne, est non magnétisé et possède une atmosphère dense : comme pour Mars, c'est la haute atmosphère et l'ionosphère du satellite qui font obstacle à l'écoulement du plasma incident. C'est un cas unique dans le système solaire par la diversité des plasmas avec lesquels il interagit en se trouvant tantôt dans la magnétosphère, tantôt dans la magnétogaine de Saturne, voire même dans le vent solaire à 12h temps local de Saturne. L'interaction du satellite avec le plasma incident dépend fortement de sa phase orbitale, qui détermine l'angle entre les directions d'arrivée du plasma incident et les photons solaires. Les 46 survols de Titan par la sonde Cassini ont été déterminés pour explorer un grand nombre de configurations afin de caractériser au mieux le voisinage du satellite. Dans le cadre de mon travail de thèse j'ai développé un modèle global tridimensionnel permettant d'étudier les interactions entre le rayonnement solaire, un plasma incident et l'environnement neutre d'un objet non magnétisé doté d'une atmosphère. Ce modèle permet de caractériser l'environnement ionisé de l'objet et de quantifier l'échappement atmosphérique. Des versions de ce modèle adaptées à Mars et à Titan doivent contribuer à l'interprétation des observations des sondes spatiales.The magnetic field of Mars is too weak to stop the solar wind flow; the high atmosphere and the ionosphere of the planet interact directly with the solar wind. The exosphere is partially ionized by solar photons, solar wind electrons, and by charge exchanges between solar wind protons and planetary neutral atoms leading to the creation of energetic neutral atoms (ENA) and cold planetary ions. These processes modify the plasma composition near the planet and participate to the mass loading of the solar wind. The interaction is strong enough to alter the atmospheric escape and can inluence the chemical evolution of the atmosphere and particularly its water content.Titan, the biggest moon of Saturn, does not possess a strong magnetic field but a dense atmosphere: similarly to Mars, the ionosphere and the atmosphere of the planet obstruct the incident plasma. Titan is a unique case in the Solar system by the diversity of the incident plasma encounters, either in the magnetosphere of Saturn, or in the magnetosheath or even in the solar wind near 12h Saturn local time. The interaction of Titan with the incident plasma depends upon its orbital phase, which determines the angle between the incoming directions of solar photons and incident plasma. The 46 flybys of Titan by Cassini have been planned to explore these various configurations in order to characterize the nearest environment of the moon. In my thesis I have developped a global three-dimensionnal model allowing to study the interaction between solar EUV, incident plasma and neutral environment of a weak or nonmagnetized body.This model allows to characterize the ionized environment of the body and quantify the atmospheric escape. Specialised versions developed for Mars and Titan can contribute to the interpretation of spacecraft observations (Mars-Express, Cassini).VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

Distribution and dynamic of plasma in the magnetospheres of venus and Mars

International audienceGeneral features of plasma characteristics in different regions of the induced magnetospheres of Venus and Mars observed by Venus Express, Mars Express and MAVEN are discussed. There are several important plasma reservoirs with different mechanisms of plasma filling and plasma energization. Among them are the ionosphere, boundary layer at the interface between the ionosphere and solar wind, plasma sheet, lobes, ion plume. Dynamics of ions in these regions is strongly controlled by the solar wind and the IMF parameters. Multi-ion origin of plasma introduces additional important features which are important for ion dynamics and filling of plasma reservoirs. The existence of crustal magnetic field on Mars modifies not only the ionosphere but also influences a filling of more remote plasma reservoirs

The Hermean bow shock and ion foreshock as seen by three-dimensional global hybrid simulations

International audienceThe thinness of the Hermean magnetosheath evidenced by Mariner 10 and MESSENGER observations results from the small average standoff distance of the Bow Shock equal to 1.45RM and has important consequences especially in the region of the parallel shock. The magnetopause is clearly identified in front of the perpendicular shock meanwhile it is hardly recognized in front of the parallel shock due to a strong interaction between the shock and the magnetospheric boundary mediated by the magnetosheath flow. This interaction is investigated by means of three-dimensional global hybrid simulations for different IMF orientations and by varying the spatial resolution of the simulations between 120 and 40km. Accordingly to MESSENGER observations (Anderson et al, 2012) the planetary magnetic field implemented in the simulations combines a dipole and a quadrupole axisymmetric sources (Richer et al, 2012).ReferencesAnderson, B. J., C. L. Johnson, H. Korth, R. M. Winslow, J. E. Borovsky, M. E. Purucker, J. A. Slavin, S. C. Solomon, M.T. Zuber, and R. L. McNutt Jr. (2012), Low-degree structure in Mercury’s planetary magnetic field, J. Geophys. Res.,117, E00L12, doi:10.1029/2012JE004159.Richer, E., R. Modolo, G. M. Chanteur, S. Hess, and F. Leblanc (2012), A global hybrid model for Mercury’s interaction with the solar wind: Case study of the dipole representation, J. Geophys. Res., 117, A10228, doi:10.1029/2012JA017898

On the Response of the near-Mercury Environment to Different Interplanetary Conditions from full-scale 3D Hybrid Simulations

International audienceWhile waiting for further insights from the upcoming data from the BepiColombo mission, this work presents some results from full-scale 3D hybrid (ions kinetic and electrons fluid) computer simulations of the near-Mercury environment under different interplanetary conditions. During its orbit Mercury passes from an high density high magnetic field intensity region (Perihelion) to a low density low magnetic field intensity region (Aphelion). Such environment change drastically influences the response of its magnetic environment, including the stand-off distance of both Bow-Shock and Magnetopause. Being these latter not distant from each other nor from the Hermean exosphere, such a dynamics may lead to important interactions between the planetary and interplanetary environments, as well as lead to unpredictable scenarios whenever the interplanetary conditions occasionally result more extreme than those average values curretly known.Here we aim to give more insights  into the near-Mercury environments under more significant interplanetary conditions by means of full-scale 3D multi-species hybrid simulations, including the Aphelion and Perihelion conditions known to date, as well as more extreme conditions, and compare these results with currently available in-situ observations and recent similar computer simulations.&#160