Quentin Nenon

Les ceintures de radiation de la planète géante Jupiter sont constituées d’électrons, de protons et d’ions lourds de très haute énergie. Ces particules chargées représentent un risque majeur pour les satellites artificiels cherchant à explorer Jupiter. Dans le même temps, comprendre l’origine et la répartition de ces particules est une problématique fondamentale du domaine de la Physique de l’Espace.Le modèle physique Salammbô de l’ONERA répond aux deux enjeux précédents. Il a été développé pour le cas de la planète géante au cours de deux thèses successives qui se sont terminées en 2004 [Santos-Costa, 2001 ; Sicard, 2004]. Les travaux précédents ont permis de mettre en place un modèle d’électron qui s’étend de l’atmosphère de Jupiter jusqu’à l’orbite d’Europe (9 Rj) et un modèle de proton jusqu’à l’orbite de la lune volcanique Io (6 Rj). Depuis cette date, la mission américaine Galileo, qui fut en orbite autour de Jupiter jusqu’en 2003, a livré de nombreuses informations sur les ceintures de radiation et sur l’environnement qui influence celles-ci.Cette thèse revisite le modèle électron et étend le modèle proton jusqu’à l’orbite d’Europe. Cela permet, en particulier, de montrer que les ondes électromagnétiques se propageant entre les orbites des lunes Io et Europe induisent des pertes significatives de particules, celles-ci étant précipitées dans l’atmosphère de Jupiter. Les modèles proposés au cours de cette thèse sont également mieux à même de prédire l’environnement extrême et limitant des ceintures de radiation que les précédents travaux.

M-MATISSE is one of the three mission candidates for the ESA M7 science mission call, all currently in Phase A with selection of the mission planned in the middle of 2026 and a possible launch at 2037. The M-MATISSE mission involves two spacecraft (Henri and Marguerite) with almost identical scientific payload to investigate the Mars plasma environment, its response to space weather, and its link with the atmosphere of the red planet. The proposed M-MATISSE configuration involves six scientific instruments on both spacecraft, two of them being consortia of several scientific sensors with common data processing units.The Solar Particle at Mars (SP@M) experiment is a part of the Mars Ensemble of Particle Instruments (M-EPI) suite of three particle sensors. SP@M will study the energy and angular distributions of 30 keV to 1 MeV electrons and 30 keV to 10 MeV ions with 4 electron and 4 ion telescopes per spacecraft. This presentation will describe the design of SP@M as achieved at the end of Phase A, ongoing development activities including digital signal processing, electron-ion discrimination, and analysis of the performances of a prototype with numerical simulations and irradiation campaigns. The scientific objectives of SP@M will also be presented, including the added value of having for the first time at Mars two observatories of suprathermal and energetic particles.

As a body without a thick atmosphere or global magnetic field, the Moon is directly exposed to incident ion fluxes from the solar wind and the terrestrial magnetosphere. As ions strike the lunar surface, they sputter individual regolith atoms, thereby contributing one component of the lunar exosphere. Previous work has studied the lunar sputtered exosphere during both nominal solar wind conditions and extreme space-weather activity such as coronal mass ejections (CMEs). These studies have suggested greater-than-tenfold increases in the lunar exospheric density during CME events due to elevated sputtering rates. Here, we analyze the effects that CMEs may have on the production and equilibrium of the sputtered neutral exosphere at the Moon via the use of in-situ solar wind measurements during CMEs. In particular, we investigate the role that heavy, highly charged minor ions in the solar wind may play during CME impacts at the Moon.For this purpose, we use measurements of the plasma moments and heavy ion composition during CMEs observed by the ACE/SWICS instrument at Sun-Earth L1 over the period of 1998–2011. We extract the solar wind flux and heavy ion composition during the event intervals listed in the publicly available “Richardson and Cane CME list” and convolve the heavy ion fluxes with appropriate sputtering yields for the lunar regolith. Generally, we find that solar wind heavy ions nominally contribute ~5% of the total sputtering yield while extreme events can reach contributions of ~20%. In no cases, however, do solar wind minor ions dominate the sputtering rates at the Moon. Finally, we discuss the implications of this work for our understanding of the full variability of the Moon’s exosphere.

Context . The search for radio signals from exoplanets or star-planet interactions is a topic of major scientific interest, as it is likely the best way to detect and measure a planetary magnetic field and, therefore, to probe the inner structure of exoplanets. However, detecting these radio emissions is challenging, since they are anisotropic by nature, sporadic, and of low intensity because of their great distances, and because the sky cannot be monitored continuously. Aims . The aim of this article is to demonstrate the relevance of using statistical tools to detect periodic radio signals in unevenly spaced observations and to identify the implications of the measured period. Methods . The identification of periodic radio signals was achieved here through a Lomb-Scargle analysis. The technique was first applied to simulated astrophysical observations with controlled simulated noise. This allowed us to characterise the origin of spurious detection peaks in the resulting periodograms - as well as to identify peaks corresponding to real periods in the studied system - and to combination or beat periods. Results . The method was validated using a real signal, with ∼1400 hours of data from observations of Jupiter’s radio emissions by the NenuFAR radio telescope over more than six years, in order to detect the periodicities of Jovian radio emissions (auroral and induced by the Galilean moons). Conclusions . We demonstrate with the simulation that the Lomb-Scargle periodogram allows us to correctly identify periodic radio signals, even in a diluted signal. On real measurements, it correctly detects the rotation period of the strong signal produced by Jupiter and the beat period of the emission triggered by the interaction between Jupiter and its Galilean moon Io, but also possibly weaker signals, such as those produced by the interaction between Jupiter and Europa or between Jupiter and Ganymede. It is important to note that secondary peaks in the Lomb-Scargle periodogram appear at the beat and combination periods among all the detected signal periodicities (i.e. real signals, but also periodicities due to regular observation intervals). These secondary peaks can then be used to strengthen the detection of weak signals. Finally, the importance of the number of observation windows used in the Lomb-Scargle analysis is discussed, as well as the data’s time and frequency resolutions in increasing its efficiency.

The SP@M (Solar Particles @ Mars) instrument, part of the M-MATISSE mission payload, is designed to measure solar energetic particles (electrons ranging from 30 keV up to 1 MeV and ions from 30 keV up to 10 MeV) using a compact detection strategy. Instead of conventional detector stacks, SP@M relies on a single 1.5 mm-thick silicon detector, where particle identification is achieved through pulse-shape analysis. This technique exploits the dependence of signal rise time on the depth of energy deposition and charge-collection dynamics. A dedicated modeling framework combining Monte Carlo simulations and charge-transport tools was first developed to pre-dimension the prototypes. It provided first-order predictions of rise time distributions for electrons, protons and alpha particles under over-depletion regime. Experimental characterizations were then performed with ¹³³Ba and ²⁰⁷Bi conversion electrons, and a tri-alpha source (²³⁹Pu, ²⁴¹Am, ²⁴⁴Cm), using controlled irradiation on both the junction and ohmic sides of the detector. The results show that the irradiation side has a critical impact: ohmic-side irradiation systematically yields longer and more dispersed rise times, enhancing species separation. For deposited energies above 600 keV, electrons and alpha particles are clearly discriminated, while below this threshold the overlap prevents reliable separation at 4.0 ns sampling. These investigations demonstrate the feasibility of PSA for charged-particle discrimination in thick silicon detectors and highlight both its potential and limitations.

The outward transport of plasma and magnetic fluxes in the gas giant magnetospheres is balanced with a return flow of flux tubes emptied through magnetic reconnection. Evidence of interchange motions between inward and outward moving flux tubes have long been reported around Jupiter and Saturn. Although amply documented at Saturn, the lack of useable low energy plasma data has prevented the analysis of their plasma properties at Jupiter. The Juno data sets allow us to characterize the plasma populations inside nine interchange events at Jupiter between M‐shells 5 and 10. We confirm that they are strongly depleted in heavy ions and low energy protons and electrons, but filled with higher energy protons and electrons. We model the pitch‐angle distribution of trapped electrons through adiabatic transport and estimate that the reported flux tubes were likely isotropic between M‐shells 11 and 35. The observed features bear strong similarities with their Kronian counterparts.

We present the first empirical‐based specification model of Saturn's plasma environment based on the analysis of all publicly available plasma moment data sets derived using multiple techniques from Cassini observations made by the Cassini Plasma Spectrometer and the Radio and Plasma Wave Science instrument. We investigate the variability of the plasma moments with respect to minimum normal distance to the current sheet, L‐shell, magnetic latitude, and magnetic local time, and find the latter three parameters to be the most useful to construct the long‐term average configuration of plasma moments in Saturn's magnetosphere. The model moments generated by the model include electron and ion densities, temperatures and ion velocities. Given that the majority of the analyzed plasma data are constrained to the equatorial region of Saturn's magnetosphere, we also present an example of extending the plasma model to larger latitudinal ranges with a physics‐based extrapolation related to plasma equilibrium. This model will be used to support future space mission planning and development for the Saturnian system, as the moon Enceladus, a planetary body that meets the major criteria for habitability, has been highlighted as a top target for large‐scale space missions by various space agencies.

Despite their importance to a variety of plasma processes in Jupiter's magnetosphere, properties of the thermal and suprathermal electrons have been sparsely reported in past literature. To address this gap, we used data from Juno 's Jovian Auroral Distributions Experiment Electron sensors to survey electron properties in Jupiter's magnetodisc between M‐shells of M = 9–40 and magnetic latitudes less than 20° within years 2016–2023. We fit the electron measurements with a sum of two anisotropic kappa distributions and provide estimates of the electron density, temperature, anisotropy, and thermodynamic kappa for the cold and hot populations, separately. We find that the electron temperature increases non‐adiabatically with M‐shell and the cold electron temperature anisotropy is most extreme near M = 15. We also provide estimates of the ambient electron properties near the Galilean moons, which should be treated with caution considering the many caveats of the fitting process, which is often associated with large uncertainties.

Energetic particle injections provide a means for fast inward radial transport and adiabatic acceleration of electrons in the magnetosphere of Jupiter. Furthermore, enhanced whistler‐mode wave activity during injections can further accelerate electrons to MeV energy. All in all, injections may contribute to the creation of the most extreme radiation belts of the solar system. In this article, we present the first survey of the >1 and >11 MeV electron fluxes observed by the Galileo mission during M = 11–20 when the flux of MeV electrons is increased by a factor of more than 3 during injection events. The Galileo observations therefore indicate that magnetospheric injections may play a dominant role for the radial transport and acceleration of MeV electrons at Jupiter, at least transiently.

Jupiter's moon Callisto orbits in a highly variable magnetospheric environment depending on its position relative to the Jovian current sheet. The Juno and Galileo missions have visited the Jovian magnetosphere and crossed Callisto's orbit several times in a variety of configurations, providing an opportunity to better characterize Callisto's orbital environment. The aim of this work is to characterize the variability of Jupiter's magnetospheric environment properties at Callisto's orbit. After identifying the time intervals during which both missions crossed the moon's orbit, Juno's charged particle data from the Jupiter Energetic Particle Detector Instrument and the Jovian Auroral Distributions Experiment are combined to build composite spectra of the electron differential fluxes and derive the electron density and pressure. Based on these observations, we provide empirical models of the energy spectrum of the electron flux for different positions. The electron densities and pressures estimated from our composite energy spectra vary from 0.2 cm ⁻³ and 0.1 nPa, respectively, at the center of the current sheet to 0.009 cm ⁻³ and 0.004 nPa, respectively, outside. We compare these observations with those obtained by the Energetic Particles Detector onboard Galileo, which reveal an additional variation of electron fluxes with local time, possibly due to a variation of the current sheet thickness. A similar comparison of magnetic field observations with the latest magnetic field models shows a good agreement. These results can be used for studying the moon‐magnetosphere interactions in preparation for the arrival of the Jupiter Icy Moons Explorer, which will perform multiple flybys of Callisto.