Proton Equatorial Pitch Angle Distributions in Jupiter's Inner Magnetosphere

Abstract

Jupiter's inner magnetosphere plasma is primarily comprised of heavy ions in the form of O n+ or S n+ and protons (H + ) (

Emission of Energetic Neutral Atoms From the Magnetosphere‐Atmosphere Interactions at Callisto and Europa

“…Sarkango et al. (2023) demonstrated the presence of a similar anisotropy in the PAD for the energy range analyzed in our study ( E ≤ 100 keV; see their Figure 1a).…”

“…If the heavier magnetospheric ion species (oxygen, sulfur) were included in our Europa ENA model, their larger gyroradii would make the emission maps appear more similar to those calculated for protons at Callisto. However, the occurrence of the band‐like structure would be largely unaffected. The anisotropic PAD observed for protons at Europa by Juno (Sarkango et al., 2023) carries elevated particle fluxes at pitch angles near 0° and 180°. Including such an anisotropic PAD in our model leaves the morphology of the detectable ENA flux largely unchanged, compared to a setup using the approximately isotropic PAD observed by Galileo (Mauk et al., 2004).…”

“…(2022) and Sarkango et al. (2023), we assume (across all considered energies) that the energetic proton flux reflects the observations by Juno: particularly, the flux perpendicular to the magnetic field is about 50% smaller than it is for pitch angles of α = 0° or 180°. For B 0 antiparallel to the z axis (as is the case in our setup for Europa at the center of the plasma sheet) we can model this PAD with the form $$$p\left(\alpha \left({\theta }_{v},{\phi }_{v}\right)\right)=1-\frac{\mathrm{sin}\,\alpha }{2}\,=\,1-\frac{\mathrm{sin}{\theta }_{v}}{2}.$$$ …”

“…In addition, Juno observations revealed a nearly isotropic proton PAD near Callisto at energies of 117 keV, that is, slightly above our considered energy range (Shen et al., 2022). A recent survey of Juno data (Sarkango et al., 2023) suggests that the proton PAD inward of Callisto's orbit may have a nonuniform shape at energies below 200 keV; that is, the proton fluxes minimize around pitch angles of α ≈ 90° and maximize at α = 0° and α = 180°. For our study, we treat the PAD near Callisto as isotropic.…”

“…In light of the upcoming JUICE mission's ENA detection capabilities, we combine the AIKEF hybrid code (Müller et al., 2011) with a particle tracing tool to model global ENA emissions from Callisto's and Europa's atmospheres. In particular, our study seeks to address the following questions: What is the effect of magnetic field line draping on the intensity and morphology of ENA emissions originating from the atmospheres of Europa and Callisto? How does the variability in the moons' plasma environments during a Jovian synodic rotation drive changes in the global ENA emission signatures? How do ENA emission intensity and morphology at these moons vary as a function of magnetospheric parent ion energy? Do the anisotropies observed in the pitch angle distribution (PAD) of energetic ions at Europa (Sarkango et al., 2023) map into the ENA emission patterns? Does Europa's localized water atmosphere, as recently identified by Roth (2021), leave a discernible imprint in the ENA emission morphology? …”