First report of electron measurements at Europa and Ganymede auroral footprint tail crossings
Abstract
Juno's polar orbit carries the Jovian Auroral Distributions Experiment (JADE) across field lines mapping to the Jovian ionospheric footprints of satellites Europa and Ganymede. When the longitudinal separation between Juno and the instantaneous satellite footprint is relatively small (up to tens of degrees down the "tail"), JADE measures a clear signature of the satellite electrodynamic interaction in keV electrons and ions. We identified multiple crossings but focus on measurements taken during the perijove 12 pass on April 1st, 2018 (DOY 091). For this Europa tail crossing, the pitch angle distribution shows a clear loss cone for electrons moving away from Jupiter and a slightly enhanced distribution of precipitating electrons. The energy distribution is a power law just before and after the crossing, and has a clear enhancement of electrons between 400 eV and 20 keV during the crossing. The Ganymede foot point crossing is puzzling at first glance because the predicted longitude of Ganymede's foot point was ahead of Juno's foot point, which means that Juno crossed ahead of the "nose" rather than the tail. This is likely due to a neglect of the magnetospheric azimuthal field not accounted for in our mapping of field lines to the middle magnetosphere. Nevertheless, the signature is clear in the electron data and shows a more remarkable surprise: JADE measures two distinct signals about 5s apart. There is a clear field-aligned electron beam precipitating into Jupiter's atmosphere and an empty upward loss cone. The energy distribution is power-law like with an enhancement of 70 eV to 2 keV electrons during the crossing. We also report an estimate of the energy flux of precipitating electrons for both crossings.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSM31A..09A
- Keywords:
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- 2704 Auroral phenomena;
- MAGNETOSPHERIC PHYSICSDE: 2756 Planetary magnetospheres;
- MAGNETOSPHERIC PHYSICSDE: 5719 Interactions with particles and fields;
- PLANETARY SCIENCES: FLUID PLANETSDE: 6220 Jupiter;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS