Claire Baskevitch

Europe, l'un des quatre satellites galiléens de Jupiter, fait l'objet d'une attention particulière de la communauté scientifique car il est susceptible d'abriter des conditions d'habitabilité favorables. La présence d'un océan d'eau liquide salée en sous-surface a été mise en évidence par l'analyse des observations de la sonde Galileo, combinée à des simulations numériques. Par ailleurs, des observations du télescope spatial Hubble et la réanalyse de données de la sonde Galileo, comparées à des simulations numériques ont renforcé l'hypothèse de la présence de panaches de vapeur d'eau. Traverser ces dernières pourrait permettre de comprendre la composition de l'océan sous-terrain.L'exploration des lunes galiléennes constitue l'un des principaux objectifs de la mission JUICE (JUpiter ICy moons Explorer) de l'ESA. En préparation des futures observations, un effort de modélisation a été entrepris pour caractériser le système magnétosphère de Jupiter-Europe. Pour caractériser l'interaction entre le plasma jovien, le champ magnétique et l'atmosphère d'Europe, j'ai utilisé le modèle LatHyS (LATMOS Hybrid Simulation). LatHyS est un modèle de simulation hybride 3D, multi-espèces et parallèle qui combine une description cinétique des ions avec une description fluide des électrons. Ce modèle de simulation nous permet de représenter la dynamique et la structure de l'environnement ionisé dans lequel baigne la lune.Mon travail a consisté à développer l'environnement d'Europe au sein de LatHyS. L'atmosphère et l'ionosphère en ont notamment été un aspect central. Les modèles d'interactions Europe-plasma jovien décrivent l'atmosphère de manière empirique et avec un modèle analytique. Cependant, j'ai mis en place une description issue d'un modèle d'exosphère planétaire 3D, appelé EGM, pour caractériser l'atmosphère d'Europe. En couplant EGM avec LatHyS, nous pouvons prendre en compte diverses espèces neutres majoritaires, intégrer des asymétries et obtenir une ionosphère plus proche de la réalité. En parallèle, j'ai développé une méthode d'optimisation qui permet de réduire la taille de l'environnement de la simulation, ce qui permet de réduire le temps d'exécution. Par la suite, j'ai réalisé de multiples simulations comparant diverses conditions neutres et ionosphériques (d'empirique à entièrement modélisées) avec des observations de Galileo afin d'étudier la réponse du système lors de ces variations. Puis j'ai analysé la réponse du plasma à un environnement théorique pendant les deux survols prévus d'Europe par JUICE. Pour finir, j'ai travaillé sur un programme qui calcule la propagation d'une onde radio dans un environnement magnétique. C'est un travail préliminaire qui a pour but d'intégrer l'environnement simulé par le modèle LatHyS dans ce code de tracé de rayon afin d'étudier la propagation des ondes radio émises par Jupiter lors d'une occultation observée par la sonde JUICE.

The JUpiter ICy moons Explorer (JUICE) mission, launched by the European Space Agency (ESA) in April 2023, aims to explore Jupiter and its icy moons, particularly focusing on Europa, Ganymede, and Callisto. This study uses the Latmos Hybrid Simulation (LatHyS) model to simulate Europa's plasma and field environment, emphasizing the upcoming JUICE flybys in July 2032. The LatHyS model, incorporating a detailed 3D exospheric model and a self‐consistent ionosphere, allows for comprehensive analysis of the moon‐plasma interactions at ion scales. Our simulations, validated against Galileo's E4 flyby data, demonstrate the model's accuracy in reproducing key features of the plasma environment and ionospheric dynamics. To characterize the system's response to neutral/ionospheric environment assumptions, we compare three simulations, with different neutral and ionosphere impacts, revealing the ionosphere's influence on the magnetic field intensity. Using an atmosphere derived from a planetary exosphere simulation model like EGM allows for the consideration of various asymmetries and multiple major neutral species, supporting further studies on ionospheric ion dynamics. Results highlight the complex interactions influenced by Europa's neutral and ionospheric conditions, providing insights for the anticipated JUICE observations. The measured signatures primarily depend on the interactions with the ionosphere along the spacecraft's trajectory and simulations show that a dense ionosphere deduced from radio occultation observations cannot reproduce the observed in situ signatures. The exosphere being a source for planetary ions, it was shown that it is significant to consider the spatial asymmetries in global interaction models in order to better account for its impact on the system.

Auroral Kilometric Radiation (AKR), the dominant radio emission from Earth, has been extensively studied, though previous analyses were constrained by limited spacecraft coverage. This study utilizes long‐term observations from Polar, Wind, and Arase spacecraft to generate comprehensive global AKR occurrence rate maps, revealing a high‐latitude and nightside preference. A detailed investigation of the equatorial shadow region confirms that the dense plasmasphere blocks AKR emissions across all wave frequencies. Low‐frequency emissions (100 kHz) propagate via plasmaspheric ducting and leakage, filling the equatorial region immediately outside the plasmasphere. Ray‐tracing simulations identify low‐density ducts within the plasmasphere as crucial channels that enable AKR to penetrate the dense plasmasphere, particularly at higher frequencies. These results align with meridional AKR observations, offering new insights into AKR propagation patterns.

Saturn Kilometric Radiation (SKR), being the dominant radio emission at Saturn, has been extensively investigated. The low‐frequency extension of SKR is of particular interest due to its strong association with Saturn's magnetospheric dynamics. However, the highly anisotropic beaming of SKR poses challenges for observations. In most cases, the propagation of SKR is assumed to follow straight‐line paths. We explore the propagation characteristics of SKR across different frequencies in this study. An extended equatorial shadow region for low‐frequency SKR is identified, resulting from the merging of the Enceladus plasma torus and the previously known equatorial shadow zone. Ray‐tracing simulations reveal that low‐frequency (100 kHz) SKR is unable to enter the shadow region and is instead reflected toward high latitudes. In contrast, high‐frequency SKR (100 kHz) generally propagates without hindrance. Observations suggest that some low‐frequency SKR can enter the shadow region through reflection by the magnetosheath or leakage from the plasma torus.

Unlike Earth, Venus doesn’t have an intrinsic magnetic field shielding it from the solar wind. However, an inducedmagnetic field is generated from the interaction of solar wind and the dense atmosphere of the planet. RecentVenus flybys by the BepiColombo mission in October 2020 and August 2021, and by Parker Solar Probe and SolarOrbiter, are unique opportunities to further study the interaction between Venus and the Sun. Observational data are essential in the study of this interaction but they are limited by the mission’s trajectory,offering a constrained view of the processes that take place. On the other hand, simulations offer a global viewof the interactions, allowing us to get results with physical significance that would not have been possible fromobservational data only. LatHyS is a three-dimensional parallel multi-species model using the hybrid formalism,that represents the electrons as a massless fluid conserving the neutrality of the plasma, and the ions by numericalmacroparticles with variable weights. Ions and electrons are coupled together using the Maxwell equations, and themacroscopic plasma parameters determine the evolution of the magnetic field (Ledvina et al. 2008). It was initiallydeveloped at LATMOS, Paris, France, for Mars (Modolo et al. 2005) and later parallelized (Modolo et al. 2016) forperformance and optimization purposes. It has the advantage of having a self consistently calculated ionosphere.LatHyS was recently adapted to the simulations of the interaction between the solar wind and Venus at IRAP,Toulouse, France (Aizawa et al. 2022). The work conducted aims at adapting a multi-grid method, initially adapted to LatHyS by Leclercq et al. 2016for the study of Mars and Ganymede, to the case of Venus. The multi-grid refinement allows a more efficient useof computing resources and an improved accuracy of the simulation thanks to a spatial resolution equivalent to orlower than the ionospheric plasma scale height. First, the multi-grid method is presented. Then, simulations using the multi-grid method on the solar wind’sinteraction with Venus are conducted, and their results are compared to simulations made using LatHyS with asingle homogeneous grid.Finally the outputs of the numerical simulations are compared to data on the magnetic field and charged particlesfrom recent flybys and from the Venus Express mission, that orbited the planet from 2006 to 2014.   References: Aizawa et al. 2022. https://doi.org/10.1016/j.pss.2022.105499 Leclercq et al. 2016. http://dx.doi.org/10.1016/j.jcp.2016.01.005 Ledvina et al. 2008. http://dx.doi.org/10.1007/s11214-008-9384-6 Modolo et al. 2005. https://doi.org/10.5194/angeo-23-433-2005 Modolo et al. 2016. http://dx.doi.org/10.1002/2015JA022324

               Galilean moons are embedded in Jupiter’s giant magnetosphere. The Jovian plasma particles interact with the atmosphere of the moons, exchanging momentum and energy, and generate different phenomena such as aurora, electric current, etc.The exploration of the Galilean moons, and in particular Ganymede and Europa, considered as potential habitats, are listed among the main objectives of the ESA JUpiter ICy moon Explorer (JUICE) mission. In preparation for future observations, a modelling effort is conducted to describe the Europa moon-magnetosphere system.               We have used the LATMOS Hybrid Simulation (LatHyS) model to characterize the Jovian plasma and magnetic field interaction with the moon and its atmosphere. The model is a hybrid 3D, multi-species and parallel simulation model which is based on a kinetic description of ions and a fluid description of electrons. The model is based on the CAM-CL algorithm and various physical processes has been implemented to describe the solar wind (or a magnetospheric plasma) interaction with Mars, Mercury, Titan, Ganymede, Earth-like body etc… (Matthews, 1994, Modolo et al, 2016, Richer et al, 2012, Modolo et al, 2008, Leclercq et al, 2015, Turc et al, 2015).  This simulation model depicts the dynamic and the structure of the ionized environment in the neighborhood of these bodies. Recently, the model has been adapted to Europa-Jupiter interaction. Global simulation results are compared to Galileo observations and will be used to illustrate the conditions that JUICE might encounter during its flybys.          References :Alan P. Matthews, Current Advance Method and Cyclic Leapfrog for 2D Multispecies Hybrid Plasma Simulations, Journal of Computational Physics, Volume 112, Issue 1, 1994, Pages 102-116, ISSN 0021-9991, https://doi.org/10.1006/jcph.1994.1084.Turc L., Fontaine D., Savoini P., Modolo R., 3D hybrid simulations of the interaction of a magnetic cloud with a bow shock, JGR, 2015Richer E, Modolo R, Chanteur GM, Hess S and Leblanc F, A Global Hybrid Model for Mercury's Interaction With the Solar Wind: Case Study of the Dipole Representation, Journ. Geophys. Res., doi:10.1029/2012JA017898, 2012Leclercq L., Modolo R., Leblanc F., Hess S., Mancini M. ,3D Magnetospheric parallel hybrid multi-grid method applied to planet-plasma interactions, Journal of Computational Physics, 309, pp.295-313, 10.1016/j.jcp.2016.01.005, 2016Modolo R., Hess S., Mancini M., Leblanc F., Chaufray J.-Y., Brain D., Leclercq L., Esteban Hernandez R., Chanteur G., Weill P., Gonzalez-Galindo F. et al., Mars-solar wind interaction: LatHyS, an improved parallel 3-D multispecies hybrid model, Journal of Geophysical Research : Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6378-6399.10.1002/2015JA022324, 2016

We model the impact of an extreme solar flare on the Mg⁺, Na⁺, O⁺ and He⁺ ion density distribution in Mercury's magnetosphere. The Flare Irradiance Spectral Model of the solar irradiance during the X9.3‐class flare on 6 September 2017 is used as input to the time‐dependent Latmos Ionized Exosphere ion density model. We find that the time‐evolution of the planetary ion distribution differs with respect to energy, location and species. There exist two ion energy populations on the dayside that experience different dynamical evolution. The peak ion density in the nightside plasma sheet is delayed by ∼7–8 min compared to the dayside. The maximum Mg⁺ density occurs ∼4 min before He⁺ and O⁺ in the whole magnetosphere. The time delay between different species does not necessarily occur for solar flares that erupt near the apparent solar limb, where the optical depth is large.