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  • 1.
    Pontoni, Angèle
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Development and simulated observations of the Jovian Neutrals Analyzer2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the development of the Jovian Neutrals Analyzer (JNA) for the Jupiter ICy moons Explorer (JUICE) mission to Jupiter, planned to launch in 2023. Jupiter, the largest planet in the Solar System, orbits the Sun at five times the distance from the Earth to the Sun, accompanied by dozens of moons, rings, and the largest object in the SolarSystem: the Jovian magnetosphere. Born of the interaction betweenthe solar wind and Jupiter’s strong magnetic field, the Jovian magneto-sphere is host to a number of unique, complex phenomena, includingthe creation of a sheet of energetic particles orbiting the giant planetand interacting with its four largest moons: Io, Europa, Ganymede, and Callisto.

    A better understanding of Jupiter’s magnetosphere and its interaction with its four largest moons is one of the main objectives of the JUICE mission. To achieve this goal, JUICE is equipped with the Particle Environment Package (PEP), comprised of six particle sensors, including JNA. By measuring low-energy Energetic Neutral Atoms (ENAs) in the range from 10 eV to 3.3 keV, JNA will image the plasma co-located with the orbit of Io, and reveal ion precipitation patterns at the surface of Jupiter’s icy moons.

    JNA improves on its predecessors (CENA on Chandrayaan-1 and ENA on BepiColombo) by featuring a higher angular resolution, with a 150◦ field-of-view divided into 11 pixels. JNA is also more resistant to radiation, a necessary improvement to be able to make measurements in the harsh radiation environment expected in the Jovian system. To measure ENAs in the low-energy range, JNA uses a charged particle deflector to remove ambient ions; a charge conversion surface to ionize incoming neutral particles, which are then energy-analyzed by an electrostatic wave system; and a Time-of-Flight cell to derive the mass of the original particle.

    In this work, we report on how JNA was designed, developed, and calibrated. We show the first results of JNA’s calibration campaign, and compare them to its expected performance. Finally, to facilitate the interpretation of JNA data at Jupiter, we estimate ENA fluxes expected at Ganymede and use our results to simulate JNA observations.

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  • 2.
    Pontoni, Angèle
    et al.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Shimoyama, Manabu
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Fatemi, Shahab
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Poppe, A.R.
    Space Sciences Laboratory, University of California, CA, Berkeley, United States.
    Wieser, Martin
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Barabash, Stas
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Simulations of Energetic Neutral Atom Sputtering From Ganymede in Preparation for the JUICE Mission2022In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 127, no 1, article id e2021JA029439Article in journal (Refereed)
    Abstract [en]

    Jovian magnetospheric plasma irradiates the surface of Ganymede and is postulated to be the primary agent that changes the surface brightness of Ganymede, leading to asymmetries between polar and equatorial regions as well as between the trailing and leading hemispheres. As impinging ions sputter surface constituents as neutrals, ion precipitation patterns can be remotely imaged using the Energetic Neutral Atoms (ENA) measurement technique. Here we calculate the expected sputtered ENA flux from the surface of Ganymede to help interpret future observations by ENA instruments, particularly the Jovian Neutrals Analyzer (JNA) onboard the JUpiter ICy moon Explorer (JUICE) spacecraft. We use sputtering models developed based on laboratory experiments to calculate sputtered fluxes of H2O, O2, and H2. The input ion population used in this study is the result of test particle simulations using electric and magnetic fields from a hybrid simulation of Ganymede's environment. This population includes a thermal component (H+ and O+ from 10 eV to 10 keV) and an energetic component (H+, O++, and S+++ from 10 keV to 10 MeV). We find a global ENA sputtering rate from Ganymede of 1.42 × 1027 s−1, with contributions from H2, O2, and H2O of 34%, 17%, and 49% respectively. We also calculate the energy distribution of sputtered Energetic Neutral Atoms (ENAs), give an estimate of a typical JNA count rate at Ganymede, and investigate latitudinal variations of sputtered fluxes along a simulated orbit track of the JUICE spacecraft. Our results demonstrate the capability of the JNA sensor to remotely map ion precipitation at Ganymede.

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