Transient aurora on Jupiter from injections of magnetospheric electrons

Jupiter's X-Ray and UV Dark Polar Region

We present 14 simultaneous Chandra X-ray Observatory (CXO)-Hubble Space Telescope (HST) observations of Jupiter's Northern X-ray and ultraviolet (UV) aurorae from 2016 to 2019. Despite the variety of dynamic UV and X-ray auroral structures, one region is conspicuous by its persistent absence of emission: the dark polar region (DPR). Previous HST observations have shown that very little UV emission is produced by the DPR. We find that the DPR also produces very few X-ray photons. For all 14 observations, the low level of X-ray emission from the DPR is consistent (within 2-standard deviations) with scattered solar emission and/or photons spread by Chandra's Point Spread Function from known X-ray-bright regions. We therefore conclude that for these 14 observations the DPR produced no statistically significant detectable X-ray signature.

Revealing the source of Jupiter's x-ray auroral flares

Jupiter's rapidly rotating, strong magnetic field provides a natural laboratory that is key to understanding the dynamics of high-energy plasmas. Spectacular auroral x-ray flares are diagnostic of the most energetic processes governing magnetospheres but seemingly unique to Jupiter. Since their discovery 40 years ago, the processes that produce Jupiter's x-ray flares have remained unknown. Here, we report simultaneous in situ satellite and space-based telescope observations that reveal the processes that produce Jupiter's x-ray flares, showing surprising similarities to terrestrial ion aurora. Planetary-scale electromagnetic waves are observed to modulate electromagnetic ion cyclotron waves, periodically causing heavy ions to precipitate and produce Jupiter's x-ray pulses. Our findings show that ion aurorae share common mechanisms across planetary systems, despite temporal, spatial, and energetic scales varying by orders of magnitude.

Juno Observations of Heavy Ion Energization During Transient Dipolarizations in Jupiter Magnetotail

Transient magnetic reconnection and associated fast plasma flows led by dipolarization fronts play a crucial role in energetic particle acceleration in planetary magnetospheres. Despite large statistical observations on this phenomenon in the Earth's magnetotail, many important characteristics (e.g., mass or charge dependence of acceleration efficiency and acceleration scaling with the spatial scale of the system) of transient reconnection cannot be fully investigated with the limited parameter range of the Earth's magnetotail. The much larger Jovian magnetodisk, filled by a mixture of various heavy ions and protons, provides a unique opportunity for such investigations. In this study, we use recent Juno observations in Jupiter's magnetosphere to examine the properties of reconnection associated dipolarization fronts and charged particle acceleration. High-energy fluxes of sulfur, oxygen, and hydrogen ions show clear mass-dependent acceleration with energy ~ m 1/3. We compare Juno observations with similar observations in the Earth's magnetotail and discuss possible mechanism for the observed ion acceleration.

Jovian Injections Observed at High Latitude

The polar orbit of Juno at Jupiter provides a unique opportunity to observe high-latitude energetic particle injections. We measure energy-dispersed impulsive injections of protons and electrons. Ion injection signatures are just as prevalent as electron signatures, contrary to previous equatorial observations. Included are previously unreported observations of high-energy banded structures believed to be remnants of much earlier injections, where the particles have had time to disperse around Jupiter. A model fit of the injections used to estimate timing fits the shape of the proton signatures better than it does the electron shapes, suggesting that electrons and protons are different in their abilities to escape the injection region. We present ultaviolet observations of Jupiter's aurora and discuss the relationship between auroral injection features and in situ injection events. We find, unexpectedly, that the presence of in situ particle injections does not necessarily result in auroral injection signatures.

Jupiter's magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits

The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno's capture orbit spanned the jovian magnetosphere from bow shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno's passage over the poles and traverse of Jupiter's hazardous inner radiation belts. Juno's energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator.