The Space Environment of Io and Europa

Bagenal, F.; Dols, V.

doi:10.1029/2019ja027485

Cited by 88 publications

(137 citation statements)

References 404 publications

(829 reference statements)

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“…The apparent strong focusing of the green lines just on the orbit of Io may mislead some viewers. One expects that the cloud of neutrals and possibly cold plasmas that serve to convert the trapped ions into ENAs have vertical and radial extents that may be as large as ±1 RJ (e.g., Bagenal & Dols, 2020). It is likely that the ENAs are coming from an extended region around the Io orbit that reflects the distribution of these components.…”

Section: Jedi Ena Viewing Analysismentioning

confidence: 99%

“…The O + S 144‐ to 209‐keV channel intensity close to Io from Figure 9 is (J (OS + ) ~ 3 × 10 3 1/(cm.s.sr.keV)). We combine that parameter with an Io neutral torus density of N = 35/cm 2 , a charge exchange cross section of σ = 7 × 10 −16 cm 2 (Figure S1 in the supporting information), and a neutral gas cloud thickness of s = 1–2 RJ (Io torus parameters reviewed by Bagenal & Dols, 2020). One finds with J (ENA) = ∫( σ N J (OS + ) d s , that J (ENA) is expected to be about 0.5 to 1/(cm.s.sr.keV).…”

Section: In Situ Characterizationmentioning

confidence: 99%

“…Smith et al (2019) showed for the Europa regions that cold ions can contribute to the neutralizing process even while neutral gases likely dominate. In Io's environment, the ratio of charged ions to neutral gases is much larger than it is for Europa (Bagenal & Dols, 2020). Hence, it may turn out to be true that charged ions, rather than neutral gases, play a dominant role in the neutralization process.…”

Section: In Situ Characterizationmentioning

confidence: 99%

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Juno Energetic Neutral Atom (ENA) Remote Measurements of Magnetospheric Injection Dynamics in Jupiter's Io Torus Regions

et al. 2020

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In planetary magnetospheres, singly charged energetic particles, trapped by the planet's magnetic field, can steal electrons from cold gas atoms and become neutralized. These now energetic neutral atoms (ENAs), no longer confined by the magnetic field, can travel out of the system similar to photons leaving a hot oven. ENAs have been used to image magnetospheric processes at Earth, Jupiter, and Saturn. At Jupiter, the opportunities to image the magnetosphere have been limited and always from the perspective of the near-equatorial plane at distance >139 RJ. The polar-orbiting Juno mission carries the Jupiter Energetic particle Detector Instrument that is serendipitously sensitive to ENAs with energies >50 keV, provided that there are no charged particles in the environment to mask their presence. Here we report on the first ENA observations of Jupiter's magnetosphere from a nonequatorial perspective. In this brief report we concentrate on emissions seen during Perijove 22 (PJ22) during very active conditions and compare them with emissions during the inactive Perijove 23 (PJ23). We observe, and discriminate between, distinct ENA signatures from the neutral gases occupying the orbit of Io (away from Io itself), the orbit of Europa (away from Europa), and from Jupiter itself. Strong ENA emissions from Io's orbit during PJ22 are associated with energetic particle injections observed near Io's orbit several hours earlier. Some injections occurred planetward of Io's L-shell (magnetic position), somewhat of a surprise given that injections are thought to be driven by outward transport of plasmas generated by Io.Plain Language Summary In the space environments of magnetized planets (magnetospheres), magnetic fields trap and confine energetic charged particles like protons and singly charged heavier ions. These ions can neutralize themselves by stealing electrons from cold gas atoms within the same environment. They become energetic neutral atoms (ENAs), and no longer confined by the magnetic field, can travel out of the system in a fashion similar to light leaving a hot oven. ENAs have been used to image magnetospheric processes at Earth, Jupiter, and Saturn. At Jupiter, the opportunities to image the magnetosphere have been limited and always from the perspective of the near-equatorial plane at large distances (>139 RJ). The polar-orbiting Juno mission carries the Jupiter Energetic particle Detector Instrument that is serendipitously sensitive to ENAs with energies >50 keV, provided that there are no charged particles in the environment to mask their presence. Here we report on the first ENA observations of Jupiter's magnetosphere from a nonequatorial perspective. That perspective allows us to observe distinct ENA signatures from the neutral gases occupying the orbit of the moon Io (away from Io itself), the gases in the orbit of the moon Europa (away from Europa), and from Jupiter itself.

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Section: Jedi Ena Viewing Analysismentioning

confidence: 99%

Section: In Situ Characterizationmentioning

confidence: 99%

Section: In Situ Characterizationmentioning

confidence: 99%

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Juno Energetic Neutral Atom (ENA) Remote Measurements of Magnetospheric Injection Dynamics in Jupiter's Io Torus Regions

et al. 2020

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“…A large fraction of these neutrals is ionized via various processes, mostly through electron impact ionization, creating a plasma torus around Jupiter in the vicinity of Io's orbit. The plasma mass loading from Io has an average rate of ∼1 ton/s (Thomas et al, ) and is the main source of plasma in Jupiter's magnetosphere (see review by Bagenal & Dols, ). The newborn iogenic ions are then picked up by Jupiter's magnetic field and immediately accelerated up to the corotation speed (∼74 km/s ) at Io's orbit via the azimuthal

\overset{normalJ}{true} \times \overset{normalB}{true}

force imposed by the outward‐propagating currents and the planet's magnetic field (Bagenal, ).…”

Section: Introductionmentioning

confidence: 99%

Survey of Ion Properties in Jupiter's Plasma Sheet: Juno JADE‐I Observations

et al. 2020

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This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE-I) sensor on Juno from 10-40 R J in the dawn to midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5-22, and the observations are separated by equatorial (|z mag [R J ]| ≤ 1.5) and off-equator (|z mag [R J ]| > 1.5) regions. Plasma parameters for H + , O + , O 2+ , O 3+ , Na + , S + , S 2+ , and S 3+ are derived by forward modeling JADE-I's energy-per-charge versus time-of-flight spectra using omnidirectional averaged convected kappa distributions and modeled instrument responses. O + and S 2+ are resolved via a ray-tracing simulation based on carbon-foil-effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to ∼20 R J . Ion number densities decrease with radial distance, the primary species being H + , O + , and S 2+ . The relative contribution of H + and S 2+ increases and decreases, respectively, in the off-equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O + to S 2+ and O n+ to S n+ number density ratios are variable, the 5 R J bin averages for O + to S 2+ ranging from ∼0.75-1.5 (equator) and ∼1.1-1.8 (off-equator) and O n+ to S n+ from ∼0.6-0.9 (equator) and ∼0.8-1.1 (off-equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 R J and range from ∼100 eV to 10 keV and 1 keV to a few tens of keV, respectively. Plain Language Summary The Jovian Auroral Distributions Experiment (JADE) on Juno hascontinuously investigated the plasma environment in Jupiter's magnetosphere since its arrival in August 2016. The polar-orbiting spacecraft enables JADE to explore both equatorial and off-equator regions of Jupiter's plasma sheet. In this study, we present plasma sheet ion characteristics such as ion composition, flow speed, and temperatures for H + , O + , O 2+ , O 3+ , Na + , S + , S 2+ , and S 3+ that are originating from the innermost Galilean satellite Io. A spatial dependence of ion characteristics is discussed and compared to previous observations. While the density profiles agree well with the Voyager-based studies, temperatures found in this study show at least an order of magnitude higher values. A new addition to this paper is that the latitudinal distribution of ions shows trend in the mass. Relative composition of protons increases compared to the heavier ions in the off-equator regions. These observations provide insights on how the ions are distributed throughout Jupiter's magnetosphere and improve our current understanding on ion dynamics in the plasma sheet. Key Points:• Ion flow speed, number density, temperature, and composition in Jupiter's plasma sheet show radial and/or latitudinal trends • H + , O + , and S 2+ are the primary ions, the contribution of H + and S 2+ increasing and decreasing, respectively, in the off-equator region • The O + to S 2+ density ratio is vari...

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“…Since Jupiter is likely not undergoing standard a Dungey cycle (McComas & Bagenal, 2007), it is also difficult to attribute magnetospheric protons to the solar wind, particularly in the inner‐most regions. Of the icy moons, Europa sustains a neutral torus of many species including hydrogen (e.g., Smith et al., 2019), which can charge exchange with the local plasma environment, however, at much lower quantities than necessary to source the magnetospheric proton population (e.g., Bagenal & Dols, 2020). The focus of this study is to constrain the ionospheric outflow source of protons.…”

Section: Introductionmentioning

confidence: 99%

Proton Outflow Associated With Jupiter's Auroral Processes

Szalay

Allegrini

Bagenal

et al. 2021

Geophysical Research Letters

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The source of protons in the Jovian magnetosphere has been historically difficult to determine experimentally. The volcanic moon Io is the primary source of plasma in the magnetosphere, inputting ∼10 3 kg s −1 of heavy ions (e.g., Bagenal & Delamere, 2011). Approximately 10% of the total magnetospheric number density is attributed to protons (e.g., Dougherty et al., 2017), which are not sourced by Io. The proton influx necessary to account for this population from 5 to 30 R J (Jovian radii) has been estimated to be 2.5-13 kg s −1 (Bodisch et al., 2017). There are at least three possible sources of protons in Jupiter's magnetosphere: solar wind, icy moons, and ionospheric outflow. Solar wind leakage across the magnetopause boundary is one possible source (e.g., Delamere et al., 2015), yet it is difficult to explain how such protons would be transported to the inner magnetosphere via this mechanism. Since Jupiter is likely not undergoing standard a Dungey cycle (McComas & Bagenal, 2007), it is also difficult to attribute magnetospheric protons to the solar wind, particularly in the innermost regions. Of the icy moons, Europa sustains a neutral torus of many species including hydrogen (e.g., Smith et al., 2019), which can charge exchange with the local plasma environment, however, at much lower quantities than necessary to source the magnetospheric proton population (e.g., Bagenal & Dols, 2020). The focus of this study is to constrain the ionospheric outflow source of protons. The outflow has been previously estimated to be 35 kg s −1 (Nagy et al., 1986) integrating over the entire polar region, and 18.7-31.7 kg s −1 (Martin et al., 2020) at high latitudes between Io's M-Shell and up to and including the auroral oval, with 4.3-8.5 kg s −1 estimated to specifically outflow from the auroral oval. Both theoretical estimates are sufficient to explain the source of protons in Jupiter's magnetosphere, but the mechanisms of ionospheric outflow have not been previously observed.

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The Space Environment of Io and Europa

Cited by 88 publications

References 404 publications

Juno Energetic Neutral Atom (ENA) Remote Measurements of Magnetospheric Injection Dynamics in Jupiter's Io Torus Regions

Juno Energetic Neutral Atom (ENA) Remote Measurements of Magnetospheric Injection Dynamics in Jupiter's Io Torus Regions

Survey of Ion Properties in Jupiter's Plasma Sheet: Juno JADE‐I Observations

Proton Outflow Associated With Jupiter's Auroral Processes

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