Evidence for electrostatic and Alfvénic accelerations in the Europa footprint tail revealed by Juno in-situ measurements
- 1IRAP-CNRS, Université Toulouse III, Toulouse, France
- 2SwRI, San Antonio, TX, USA
- 3LAM, CNRS, CNES, Marseille, France
- 4Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA
- 5Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
- 6Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA
- 7Institute for Space Astrophysics and Planetology, National Institute for Astrophysics, Rome, Italy
- 8NASA Goddard Space Flight Center, Greenbelt, MD, USA
- 9Space Research Corporation, Annapolis, MD, USA
Moon-magnetosphere interactions result from the encounter between a magnetospheric plasma flow and moons, which act as obstacles to the plasma flow. In the Jovian magnetosphere, the Galilean moons orbit with a Keplerian velocity much slower than the plasma velocity, driven in near corotation by the planetary magnetic field. Therefore, they disturb the magnetospheric plasma flow, which in turn generates Alfvén waves in their close environments. These waves propagate along the magnetic field lines, accelerating particles and triggering auroral emissions in the giant planet atmosphere.
Since August 2016, the Juno mission has made it possible to characterize in-situ the moon-magnetosphere interactions. Several crossings of the flux tubes connected to the orbits of the Galilean moons have been reported, revealing a diversity of particle properties and acceleration processes. However, Europa-magnetosphere interaction, whose remote and in-situ signatures are weaker and more difficult to identify than those of Io, remain poorly known.
We characterize the precipitating electrons accelerated in the Europa-magnetosphere interaction by analyzing in-situ measurements and remote sensing observations recorded during 10 crossings of the flux tubes connected to Europa's auroral footprint tail by Juno. The electron downward energy flux exhibits an exponential decay as a function of down-tail distance from Europa's main auroral spot, with an e-folding factor of 7.2°. Electrons are accelerated at energies between 0.3 and 25 keV, with a characteristic energy that decreases down‐tail. We show that in the near tail (∆λFrac < 6°), acceleration is due, at least in part, to electrostatic processes while in the far tail (∆λFrac > 6°) broadband energy spectra are evidence for Alfvénic acceleration. The size of the interaction region at the equator is estimated to be 4.5 Europa radii, consistent with previous estimates based on theory and UV observations.
How to cite: Rabia, J., Hue, V., Szalay, J. R., André, N., Nénon, Q., Blanc, M., Allegrini, F., Bolton, S. J., Connerney, J. E. P., Ebert, R. W., Greathouse, T. K., Louarn, P., Mura, A., Penou, E., and Sulaiman, A. H.: Evidence for electrostatic and Alfvénic accelerations in the Europa footprint tail revealed by Juno in-situ measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7025, https://doi.org/10.5194/egusphere-egu23-7025, 2023.
