Method to Derive Ion Properties From Juno JADE Including Abundance Estimates for O⁺ and S²⁺

Abstract

The Jovian Auroral Distributions Experiment Ion sensor (JADE‐I) on Juno is a plasma instrument that measures the energy‐per‐charge (E/Q) distribution of 0.01 to 46.2 keV/q ions over a mass‐per‐charge (M/Q) range of 1– 64 amu/q. However, distinguishing O+ and S2+ from JADE‐I's measurements is a challenging task due to similarities in their M/Q (∼16 amu/q). Because of this, O+ and S2+ have not been fully resolved in the in situ measurements made by plasma instruments at Jupiter (e.g., Voyager PLS and Galileo PLS) and their relative ratios has been studied using physical chemistry models and ultraviolet remote observations. To resolve this ambiguity, a ray tracing simulation combined with carbon foil effects is developed and used to obtain instrument response functions for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+. The simulation results indicate that JADE‐I can resolve the M/Q ambiguity between O+ and S2+ due to a significant difference in their charge state modification process and a presence of a large electric potential difference (∼8 kV) between its carbon foils and MCPs. A forward model based on instrument response functions and convected kappa distributions is then used to obtain ion properties at the equatorial plasma sheet (∼36 RJ) in the predawn sector of magnetosphere. The number density ratio between O+ and S2+ for the selected plasma sheet crossings ranges from 0.2 to 0.7 (0.37 ± 0.12) and the number density ratio between total oxygen ions to total sulfur ions ranges from 0.2 to 0.6 (0.41 ± 0.09).

Energetic Oxygen and Sulfur Charge States in the Outer Jovian Magnetosphere: Insights From the Cassini Jupiter Flyby

“…Total 95.9 keV/e oxygen ion flux (O + + O 2+ ) was 56% of the combined 95.9 keV/e oxygen and sulfur ion flux making the O n+ to S n+ ratio~1.3. This agrees well with early results at higher energies from Voyager 1 and 2 in the outer magnetosphere (Hamilton et al, 1981), comparable to neutral cloud models (matching ultraviolet emissions) at thermal energies near 9 R J (Delamere et al, 2005), but is greater than the Juno kappa fits from Kim et al (2019) at~35 R J .…”

“…This is higher than estimated by Kim et al () near 35 R J of 53% at Juno compared to 26% at Cassini, suggesting the relative abundance of O + and S 2+ (m/q = 16 amu/ e ) particles changes as the plasma is transported to the outer magnetosphere. Total 95.9 keV/ e oxygen ion flux (O + + O 2+ ) was 56% of the combined 95.9 keV/ e oxygen and sulfur ion flux making the O n+ to S n+ ratio ~1.3. This agrees well with early results at higher energies from Voyager 1 and 2 in the outer magnetosphere (Hamilton et al, ), comparable to neutral cloud models (matching ultraviolet emissions) at thermal energies near 9 R J (Delamere et al, ), but is greater than the Juno kappa fits from Kim et al () at ~35 R J .…”

“…Panels C and D illustrate the percentage of flux in each charge state for sulfur (oxygen). Panel E shows the relative flux abundance of 95.9 keV/ e oxygen and sulfur from this study (green) and from Kim et al () (pink). Previously published relative densities are shown in Panel F. Error bars are included for surveys of multiple events to denote the maximum and minimum of the relative abundance within that study.…”

“…Most outer magnetospheric 95.9 keV/e oxygen is O + (96% of oxygen ions), with the remaining oxygen ions being O 2+ (4% of oxygen ions). This dominance of O + is different from the inner and middle magnetosphere (e.g., Clark et al, 2016;Geiss et al, 1992;Kim et al, 2019). This could suggest either preferential acceleration of O + to 95.9 keV/e or processes such as charge exchange and ionization and modify the relative abundance of oxygen charge states as the plasma is transported outward.…”

“…This could suggest a charge‐dependent heating and/or energization effects in the outer magnetosphere or an energy dependence of the charge state abundance. Most outer magnetospheric 95.9 keV/ e oxygen is O + (96% of oxygen ions), with the remaining oxygen ions being O 2+ (4% of oxygen ions). This dominance of O + is different from the inner and middle magnetosphere (e.g., Clark et al, ; Geiss et al, ; Kim et al, ). This could suggest either preferential acceleration of O + to 95.9 keV/ e or processes such as charge exchange and ionization and modify the relative abundance of oxygen charge states as the plasma is transported outward. The flux of 95.9 keV/ e O + was ~3 times higher than for S 2+ .…”