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Loss of Energetic Ions Comprising the Ring Current Populations of Jupiter's Middle and Inner Magnetosphere
Journal article   Open access   Peer reviewed

Loss of Energetic Ions Comprising the Ring Current Populations of Jupiter's Middle and Inner Magnetosphere

B. H. Mauk, F. Allegrini, F. Bagenal, S. J. Bolton, G. Clark, J. E. P. Connerney, D. J. Gershman, D. K. Haggerty, V. Hue, M. Imai, …
Journal of geophysical research. Space physics, Vol.127(5), e2022JA030293
05/2022
DOI: 10.1029/2022JA030293
url
https://doi.org/10.1029/2022JA030293View
Published (Version of record) Open Access

Abstract

The low‐altitude, polar orbit of the Juno mission allows the Jupiter Energetic Particle Detector Instrument to view into, and resolve, the loss cone of energetic ions comprising the low‐altitude extension of Jupiter's ring current ions. For regions mapping from just inside Ganymede's orbit to well beyond Ganymede's orbit, energetic ions (>50 keV H+ and >130 keV Oxygen and Sulfur ions) are strongly scattered into the loss cone and lost to the magnetosphere at the “strong diffusion limit” at essentially all times. We conclude, by arguing against magnetic curvature scattering, that the cause is waves, perhaps associated with Alfvénic variations previously documented in this equatorial region. Scattering is generally weak or nonexistent near the orbits of the moons Europa and Io, except for the regions just downstream of the corotating plasmas. For Io, we sometimes observe moderate, but not saturated, scattering within roughly 60° downstream. Significantly, scattering is weak or nonexistent just upstream of Io's position, an asymmetry echoed in some previous wave observations. A preliminary accounting of the total (longitude‐averaged) scattering losses near Io's orbit yields loss rates of order 4%–5% of the strong diffusion limit for H+ and 5%–7% for heavy ions (O + S). We conclude that near Io's orbit, charge exchange losses likely dominate over scattering losses for heavy ions and for the lower energy H+ ions (roughly <200 keV). Plain Language Summary The space environments (magnetospheres) of magnetized planets are populated by energetic charge particles (ionized atoms, or ions, and electrons) encircling the planets. These particles carry a ring‐like electric current that distorts the magnetic field away from its nominal “dipole” configuration, familiar from classroom experiments with magnets and iron filings. Here, we examine the loss of these ring current charged particles in Jupiter's middle and inner magnetosphere. The Juno spacecraft, now orbiting Jupiter with a polar, cloud‐skimming trajectory allows us, for the first time, to look upward from low altitude and measure the quantity of charged particles that are lost by precipitating onto Jupiter's atmosphere. We find that in the middle magnetosphere, between the orbits of the moons Ganymede and Callisto, the ions are surprisingly lost at the maximum possible rate for precipitation, a rate called the “strong diffusion limit.” In the regions closer to Jupiter, in the vicinity of the moons Europa and Io, the ions are lost from precipitation at a much lower rate. But in addition, the local interactions between these two moons and the space environments close to the moons have profound influences on how fast the ions are being lost due to precipitation. Key Points Jupiter ring current energetic ions near and outside Ganymede's orbit are scattered into the loss cone at the strong diffusion limit Near the Io and Europa orbits, scattering into the loss cone is very low except within ∼60° of the downstream positions of the moons Near Io's orbit, charge exchange losses dominate over losses from scattering for heavy ions and lower energy (<∼200 keV) protons
 Precipitation energetic particles Jupiter losses magnetosphere ring current

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