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

Abstract

Published in: ScienceLink to article, DOI: 10.1126/science.aam5928 Publication date: 2017 Document VersionPeer reviewed version Link back to DTU Orbit Citation (APA): Connerney, J. E. P., Adriani, A., Allegrini, F., Bagenal, F., Bolton, S. J., Bonfond, B., ... Waite, J. (2017). Jupiter's magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits. Science, 356(6340) Abstract: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 ~4,000 kilometers above the cloudtops 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.One Sentence Summary: Juno's instruments provide complete polar maps of Jovian UV aurorae, spatially resolved images of the IR southern aurorae, and in-situ direct measurements of precipitating charged particle populations exciting the aurora. only one bow shock upon approach suggests that the magnetosphere was expanding in size, a conclusion bolstered by the multiple BS encounters experienced outbound during the 53.5 day capture orbit at radial distances of 92-112 Rj before apojove on DOY 213 (~113 Rj), and at distances of 102-108 Rj thereafter . Apojove during the 53.5day orbits occurred at a radial distance of ~113 Rj, so Juno resides at distances of >92 Rj for little more than half of its orbital period (~29 days). Thus on the first two orbits, Juno encountered the MP boundary a great many times at radial distances of ~81-113 Rj.Juno's traverse through the well-ordered portion of the Jovian magnetosphere is illustrated in The magnetic field observed in the previously unexplored region close to the planet (radius<1.3Rj) was dramatically different from that predicted by existing spherical harmonic models, revealing a planetary magnetic field rich in spatial variation, possibly due to a relatively large dynamo radius [1]. Perhaps the most perplexing observation was one that was missing: the expected magnetic signature of intense field aligned currents (Birkeland currents) associated with the main aurora. We did not identify large magnetic perturbations associated with Juno's traverse of field lines rooted in the main auroral oval (supplementary material).Juno's Waves instrument made observations of radio and plasma wave phenomena throughout the first perijove ( Figure 2). These observations were obtained at low altitudes whilst crossing magnetic field lines...

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

“…The previous work discussed earlier focused on ions with incident energies between 1 and 2 MeV/u, as these high ion energies are responsible for X‐ray emissions. However, we now know that ions with a wide range of energies precipitate into the polar cap, as confirmed by National Aeronautics and Space Administration (NASA)'s Juno spacecraft (Clark, Mauk, Haggerty, et al, ; Clark, Mauk, Paranicas, et al, ; Connerney et al, ; Haggerty et al, ; Szalay et al, ). Hence, we now model a much broader range of incident ion energies than previously considered (i.e., from 10 keV/u to 5 MeV/u).…”

Bar Code Events in the Juno‐UVS Data: Signature ∼10 MeV Electron Microbursts at Jupiter

“…As it cruised through the large-scale magnetopause boundary layer, its instruments measured intense bursts of radio emissions and energetic particles (both electrons and protons), with timescales ranging from 2 to 80 min (Karanikola et al, 2004;MacDowall et al, 1993;McKibben et al, 1993;Zhang et al, 1995). The instrument suite and the polar orbit of the Juno spacecraft are well suited to perform this investigation Bolton et al, 2017;Connerney et al, 2017). At the onset of the electron and proton bursts, the pitch angle distributions were field aligned and monodirectional, with the particles originating from Jupiter's aurora.…”

Constraining Jupiter's internal flows using Juno magnetic and gravity measurements

“…The strong magnetic field of Jupiter (around 6 Gauss at the surface) could affect the flow field at depth with modestly high electrical conductivity [Liu et al, 2008;Heimpel and Gómez Pérez, 2011;Gastine et al, 2014;Jones, 2014;Connerney et al, 2017]. The strong magnetic field of Jupiter (around 6 Gauss at the surface) could affect the flow field at depth with modestly high electrical conductivity [Liu et al, 2008;Heimpel and Gómez Pérez, 2011;Gastine et al, 2014;Jones, 2014;Connerney et al, 2017].…”