Jupiter's Ion Radiation Belts Inward of Europa's Orbit

Abstract

Jupiter has the largest magnetosphere in the solar system and electron radiation belts with the highest energies (Mauk & Fox, 2010;. It has been visited by several spacecraft (Krupp et al., 2004), yet there are regions in physical space and particle energy that are not well explored (Roussos et al., 2019). High intensities of either electrons or protons can impact the integrity of in-situ radiation measurements Mauk et al., 2016;Nénon, Sicard, Caron et al., 2018), which becomes an issue inward of the orbit of Io and makes reliable measurements in this region particularly rare. NASA's Juno mission-a Jupiter polar orbiting spacecraft-frequently, albeit briefly, visits Jupiter's radiation belts and is equipped with energetic particle instrumentation. Here we present a careful analysis of data obtained by its JEDI instrument (Section 2.1) and filter the measurements to select reliable measurements (Section 3). We use that data to study the physics of the innermost radiation belt (Section 4

Energetic Proton Distributions in the Inner and Middle Magnetosphere of Jupiter Using Juno Observations

“…range of first adiabatic invariant μ (Paranicas et al, 1990). The ion PSD profiles derived from the Juno observations within Europa's (M ∼ 9.5) orbit were analyzed and used to indicate a source of inner belt ions coming from inward radial transport (Kollmann et al, 2021). A recent study that extended to radial distances of M = 25 showed an almost continuously increasing radial PSD as M-shells increase at energies above 1,000 MeV/G (Garrett & Jun 2021).…”

Losses of Radiation Belt Energetic Particles by Encounters With Four of the Inner Moons of Jupiter

“…Jupiter is well known to have the largest magnetosphere in the solar system and electrons radiation belts with the highest energies (e.g., Mauk & Fox, 2010;. Surrounded by intense and energetic radiation belts, the radiation conditions of Jupiter are more extreme inside the Europa's orbit than outside regions (e.g., Kollmann et al, 2017Kollmann et al, , 2021Woodfield et al, 2014). Six moons orbit around Jupiter inside L < 10 (Metis: Φ = 40 km, L = 1.84, and e m = 0.0077; Adrastea, Φ = 16 km, L = 1.84, and e m = 0.0063; Amalthea: Φ = 167 km, L = 2.59, and e m = 0.0075; Thebe: Φ = 98 km, L = 3.17, and e m = 0.018; Io: Φ = 3,637.4 km, L = 6.01, and e m = 0.0041; Europa: Φ = 3,121.6 km, L = 9.57, and e m = 0.009).…”

“…Due to the absorption loss by Europa, the particle fluxes can also exhibit a minimum around this orbit. Interestingly, absorption at Europa mostly shows for >10 MeV ions(Kollmann et al, 2021) and otherwise only affects particles in its immediate vicinity (e.g.,Paranicas et al, 1998;Kollmann et al, 2018), even though absorption times are smallest for the lowest energies. The reason for this is likely the competition between absorption and other processes that resupply energetic particles at low energies.…”

“…Europa also may play a role in removing transient Jovian radiation belt particles such as the "C22 transient" (e.g.,Hao et al, 2020). While the particle losses caused by encounters with Amalthea and Thebe are much slower, the absorption depletion of energetic particle by these two moons may contribute to the formation of several discrete ion radiation belts found roughly inside L < 4 (e.g.,Kollmann et al, 2021). Furthermore, on basis of the distinct profiles of average particle lifetimes at different energies with different equatorial pitch angles corresponding to the moon absorption, it is inferred that the pitch angle distribution could likely follow the 90°-peaked type for energetic electrons but exhibit a V-type feature for energetic protons and that there may exist a peak of electron fluxes at ∼tens of MeV, a feature that currently cannot be resolved with the existing measurements that integrate over large energy ranges.…”

Jupiter missions as probes of dark matter

“…The precise determination of τ loss is highly non-trivial. Such modeling may benefit from matching with other in situ data such as the fluxes of non-relativistic ions [92] or magnetic fields [93]. We will not pursue an accurate modeling of τ loss in our paper.…”