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  • First Report of Electron Me...
    Allegrini, F.; Gladstone, G. R.; Hue, V.; Clark, G.; Szalay, J. R.; Kurth, W. S.; Bagenal, F.; Bolton, S.; Connerney, J. E. P.; Ebert, R. W.; Greathouse, T. K.; Hospodarsky, G. B.; Imai, M.; Louarn, P.; Mauk, B. H.; McComas, D. J.; Saur, J.; Sulaiman, A. H.; Valek, P. W.; Wilson, R. J.

    Geophysical research letters, 28 September 2020, Letnik: 47, Številka: 18
    Journal Article

    We report the first in situ observations of electron measurements at a Europa footprint tail (FPT) crossing in the auroral region. During its 12th science perijove pass, Juno crossed magnetic field lines connected to Europa's FPT. We find that electrons in the range ~0.4 to ~25 keV, with a characteristic energy of 3.6 ± 0.5 keV, precipitate into Jupiter's atmosphere to create the footprint aurora. The energy flux peaks at ~36 mW/m2, while the peak ultraviolet (UV) brightness is estimated at 37 kR. We estimate the peak electron density and temperature to be 17.3 cm−3 and 1.8 ± 0.1 keV, respectively. Using magnetic flux shell mapping, we estimate that the radial width of the interaction at Europa's orbit spans roughly 3.6 ± 1.0 Europa radii. In contrast to typical Io FPT crossings, the instrument background caused by penetrating energetic radiation (> ~5–10 MeV electrons) increased during the Europa FPT crossing. Plain Language Summary Jupiter's moons interact with Jupiter's space environment, or magnetosphere, and create auroral spots and tails in Jupiter's ionosphere. Io's aurora footprint on Jupiter is the strongest and most persistent of all moons, but Ganymede, Callisto, and Europa's auroral footprints are also routinely observed by remote platforms. NASA's Juno mission and its instrument suite occasionally fly through regions that are connected to the moon‐magnetosphere interactions. During these crossings, Juno samples the electrons and ions that create the aurora. This paper is the first report of electron measurements taken during a Juno crossing of Europa's tail. These measurements confirm previous results based on remote observations. Most importantly, they provide a sample of the conditions in the regions associated with Europa's footprint aurora in Jupiter's magnetosphere. Key Points This is the first report of in situ electron measurements of a Europa footprint tail crossing Precipitating electron energies range from ~0.4 to ~25 keV with a characteristic energy of 3.6 keV, consistent with a low color ratio of the auroral emissions The instrument background caused by > ~5–10 MeV penetrating electrons increased during the crossing, opposite to what is observed at Io