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Reference : UMR8190-RONMOD-001
Workplace : PARIS 05
Date of publication : Monday, September 07, 2020
Scientific Responsible name : Ronan Modolo
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Europa, one of the four Galilean moon of Jupiter, is subject of recent interest from the planetology and space physics community to determine whether the icy moon could harbour conditions suitable for life. Re-analysis of in-situ Galileo observations, combined with simulation results, brought new independent insights on the presence of a moon subsurface liquid water reservoir that may be venting plumes of water vapor above its icy shell [Jia et al, 2018]. Such findings are also supported by previous ultraviolet images from Hubble Space Telescope which suggested the presence of plumes [Roth et al, 2014].
The JUICE (ESA) and EUROPA Clipper (NASA) mission objectives are to explore this unique environment. In this context, this thesis proposes to support future observations by developing a three-dimensional model of the Jovian plasma interaction with the Europa's environment.
Europa, one of the four Galilean moon of Jupiter, is subject of recent interest from the planetology and space physics community to determine whether the icy moon could harbor conditions suitable for life. Re-analysis of in-situ Galileo observations, combined with simulation results, brought new independent insights on the presence of a moon subsurface liquid water reservoir (ocean ?) that may be venting plumes of water vapor above its icy shell [Jia et al, 2018]. Such findings are also supported by previous utlraviolet images from Hubble Space Telescope which suggested the presence of plumes [Roth et al, 2014].
The JUICE (JUpiter ICy moon Explorer) mission, selected by ESA in May 2012 to be the first large mission within the Cosmic Vision Program 2015–2025, will provide the most comprehensive exploration to date of the Jovian system in all its complexity, with particular emphasis on Ganymede as a planetary body and potential habitat. Investigations of the neighbouring moons, Europa and Callisto, will complete a comparative picture of the environmental conditions on the Galilean moons and their potential habitability. In this context two flybys of Europa are planned. In addition, NASA has recently confirmed the EUROPA Clipper mission to explore Jupiter's moon and to investigate its habitability. Therefore, this PhD is timely in line with the programmatic context of space agencies, and will be essential to respond to request from operation teams (eg ESAC/ESTEC).
The Galilean satellites are known to have thin atmospheres, technically exospheres (McGrath et al., 2004), produced by ion-induced sputtering and sublimation of the surface materials. These moons and tenuous atmosphere are embedded in the flowing plasma of the jovian magnetosphere (region of space governed by the intrinsic magnetosphere of the planet). The interaction between the neutral environments of the Galilean satellites and the jovian plasma changes the plasma momentum, the temperature and generates strong electrical currents. The exact nature of the interaction, and physical processes involved, depends on various intrinsic properties of the moons (Neubauer et al, 1998).
Models of the magnetospheric interaction [Saur et al., 1998; Lipatov et al., 2010] indicate that plasma currents above the surface constitute major backgrounds for detection of the intrinsic oceanic signals, and must be substracted to deduce the induced magnetic field [Sittler et al, 2010]. The background current contribution from hot ionospheric ions and pick-up ions must be determine carefully to characterize the salty ocean.
In order to prepare the future observations, we will conduct simulation efforts to describe the ionized environment of the moon, particularly in the frame of JUICE in which R. Modolo is co-I and B. Cecconi is co-PI of the Radio and Plasma Wave Instruments consortium. We will use the generic multi-species parallel 3D model LatHyS [Modolo et al, 2016] to characterize the moon – magnetosphere interaction. The simulation model is based on the so called 'hybrid' formalism where ions are described by a set of numerical particles (called macro-particles) with adjustable weight while electrons are represented by an inertialess fluid conserving the charge neutrality of the plasma. Ions and electrons are coupled via Maxwell's equations. The temporal evolution of electromagnetic fields and the motion of charged particles are computed self-consistently retaining kinetic effects for ions, contrarily to MHD models. In addition, the multi-species nature of the code LatHyS allow us to described the dynamic of all ion species (jovian and ionospheric ion species).
The LatHyS model has been successfully used to characterize the ambient plasma (solar wind or magnetospheric) interaction with planetary environment such as Mars, Mercury, Titan, Earth and Ganymede [eg Modolo et al, 2015 ;2016 ; Leclercq et al, 2016]. We will use the multi-grid version of the model developed for Ganymede (Figure 1) and adapt it to Europa's environment.
The ionospheric plasma will be determined by the ionization of Europa's neutral atmosphere. The LatHyS model takes into account photoionization, electron impact and charge exchange processes. In order to have a careful description of the ion production, we will use the output of the Exospheric Global Model developed at LATMOS by Leblanc et al, [2017a] and Oza et al [2018,2019]. This model will give a three-dimensional map of O2 density at various Jupiter local times. In addition, Leblanc et al, [in preparation] are currently working on a plume of water vapor description.
The different regions (atmosphere, ionosphere, magnetosphere) are coupled together, exchanging energy and momentum between the different layers/interfaces. None of these models can describe all regions governed by different physical processes and temporal/spatial scales. A first approach followed by our group has been to couple different models, i.e. to use the outputs of a model as initial or boundary conditions for the other models. This strategy have been successfully applied within ANR projects HELIOSARES (for Mars, 2009-2014), MARMITE (for Mercury, 2014-2018) and TEMPETE (2018-2022).
Thanks to the ARTEMIS-P (Anisotropic Ray Tracing for ElectroMagnetism in Magnetosphere, Ionosphere and Solar wind including Polarization) code [Gautier 2013], we will evaluate the effect of the modeled plasma environment on the propagation of radio waves in the vicinity of the moon. This will allow us to evaluate the capabilities of using the propagation effects and the occultation of the radio waves coming from the Jovian natural low frequency radio sources, to probe the moon ionosphere with the radio receiver onboard JUICE.
Both JUICE and EUROPA Clipper are in preparation phase (C/D/E1 for JUICE) with a possible launch in 2022 for JUICE and 2025 for EUROPA Clipper. JUICE Europa's flyby is planned for 2030 while the schedule for the multiple Europa flybys is not detailed yet for EUROPA Clipper. Although the schedule seems to be far from now, ESA requires to defined operation modes now (Working Group 3) to optimize the allocated telemetry for various instruments and defined the high collection rate periods for RPWI.
The PhD thesis has two combined objectives : 1- described the plasma environment in the vicinity of the icy moon in order to understand the exchange of energy and momentum between the jovian plasma and Europa's atmosphere ; 2- to make use of this 3D ionosphere/magnetosphere to determine wave propagation properties of radio emissions and predict radio occultation.
During the last fifteen years, we have conducted a modeling effort to develop, parallelize and implement various physical processes in the global simulation model called LatHyS (Latmos Hybrid Simulation, Modolo et al. ) to describe the plasma interaction with planetary environments.
This simulation models have been adapted to Mars [Modolo et al, 2005,2006, 2012,2016,2018 ; Romanelli et al, 2019], Mercury [Richer et al, 2012] , Earth [Turc et al 2015], as well as Titan [Modolo et al, 2007 ; 2008] and Ganymede [Leclercq et al, 2016 ; Carnielli et al, 2019 ;2020]. In addition, a 3D multi-species Exospheric Global Model (EGM) at LATMOS. The neutral exospheric model is a 3D Monte Carlo model that describes the fate of several species around Mars [Leblanc et al. 2017b], Mercury [Leblanc and Johnson 2010], Ganymede [Leblanc et al. 2017a], the Moon [Leblanc and Chaufray 2011] and Europa [Oza et al. 2017]. Further developments of the model to include the plume of water vapor is in progress and result of a collaboration with IDES laboratory. This project is based on this coupling and will use the infrastructure developed during previous and current ANR and FP7 projects. The developments will be validated by comparing simulation results with Galileo in-situ observations like it has been done successfully for Mars [eg Modolo et al, 2018 ; Romanelli et al, 2019], and Ganymede [Leclercq et al, 2015 ; Carnielli et al, 2019].
The ARTEMIS-P code has been developed by a former PhD student at LESIA and has been tested and applied on use cases at Earth and Saturn. During the PhD thesis, the code will be put online, using a run-on-demand job management system already in place at Observatoire de Paris. This part will be conducted with the support of the Paris Astronomical Data Centre (PADC). The moon plasma environment model will have to be interfaced with the ARTEMIS-P code.
The PhD is planned to be held in both laboratories (LATMOS and LESIA) with a co-supervision (R. Modolo and B. Cecconi). Thanks to the large collaboration network developed by both supervisors, the PhD student will benefit of priviliged contact with Ile-de-France scientists as well as national and international teams (eg JUICE-RPWI team). The project will subscribe in a solid collaboration started many years ago between the two laboratories. The project aims to build a global model describing the neutral and ionized environment from the surface to few planet radii with various scale height. This challenge has been successfully achieved on Ganymede and drove collaboration on the ionospheric description of the moon with A. Galand (Imperial College, UK). For Europa the presence of the plume of water vapor is modeled by F. Leblanc (LATMOS) and colleagues from IDES laboratory, leading to inter-disciplinary collaboration.
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