Energetic Proton Distributions in the Inner and Middle Magnetosphere of Jupiter Using Juno Observations. Issue 16 (26th August 2022)

• Record Type: Journal Article
• Authors: Shen, Xiao‐Chen; Li, Wen; Ma, Qianli; Nishimura, Yukitoshi; Daly, Alec; Kollmann, Peter; Mauk, Barry; Clark, George; Bolton, Scott
• Is Part Of: Geophysical research letters. Volume 49:Issue 16(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-26
• Subjects: phase space density -- pitch angle distribution -- proton -- Jupiter -- Juno -- ion; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL099832
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Jupiter is known to have a complex magnetosphere containing energetic (above 10s of keV) electrons, protons, and heavy ions. However, a global distribution of these energetic particles is not fully understood before the era of the polar‐orbiting Juno mission. In this study, we focus on the energetic proton distribution at M < 50 by taking advantage of Juno's measurement covering various magnetic latitudes and M ‐shells, and find that energetic proton fluxes are higher off‐equator than that near the equator at M > ∼20, and become comparable or lower at high latitudes than those near the equator at low M ‐shells. Pitch angle distributions of energetic protons are field‐aligned, isotropic, and weak pancake‐like from high to low M ‐shells. Proton phase space density shows a weak M ‐shell dependence at M > 30 and a large positive slope at M < 30, suggesting their potential source and loss processes. Plain Language Summary: Jupiter has a strongly magnetized magnetosphere, which traps electrons and ions with a broad energy range. Before the arrival of Juno at Jupiter, there were limited observations of particles at high latitudes. By taking advantage of high‐quality energetic proton observations from Juno, we evaluate the global distribution of energetic protons at Jupiter. The statistical results suggest that energetic proton flux is mostly comparable or even higher at high latitudes compared to that near the equator, which is consistent with their equatorial pitch angle distributions showing mostly field‐aligned and isotropic, except for a weak pancake feature at low M ‐shells. Furthermore, the radial proton phase space density profile shows a weak M ‐shell dependence at M > 30 and a large positive slope at M < 30. The underlying mechanisms related to the observed statistical pattern of proton distributions are discussed. Key Points: A statistical survey of energetic proton flux at various M ‐shells ( M < 50) and magnetic latitudes is performed using Juno observations Pitch angle distribution of energetic protons is mostly field aligned at M > 25 and tends to become pancake‐shaped at smaller M‐ shells Phase space density of equatorial protons increases with increasing M ‐shell at M ∼7–30 and keeps almost the same beyond M ∼ 30