First Report of Electron Measurements During a Europa Footprint Tail Crossing by Juno
F. Allegrini, G. R. Gladstone, Vincent Hue, G. Clark, J. R. Szalay, W. S. Kŭrth, F. Bagenal, S. J. Bolton, J. E. P. Connerney, R. W. Ebert, T. K. Greathouse, G. B. Hospodarsky, Masafumi Imai, P. Louarn, B. H. Mauk, D. J. McComas, Joachim Saur, A. H. Sulaiman, P. W. Valek, R. J. Wilson
Abstract
Abstract 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/m 2 , 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.