Probing Jupiter-satellite interactions from the beaming of their decametric emissions: the case of Europa and Ganymede

Abstract

In a recent study, we accurately measured the beaming of Io-Jupiter decametric emissions, whose uncertainty is controlled by that on the position of the active Io ux tube (IFT) hosting the radiosources. The active IFT was positioned by 3 different methods using either simultaneous radio/UV measurements, either bi-point radio measurements, or independent models of equatorial lead angle. We found largely oblique beaming angles θ within 70 - 80° from the local magnetic field vector, decreasing with increasing frequency. Assuming that Io-Jupiter radio emissions are driven by the electron cyclotron maser from loss cone electron distribution functions, we then derived the kinetic energy of unstable electrons E_e- associated to each time-frequency measurement of Io-Jupiter decametric arcs, ranging from 3 to 16 keV. Both θ and E_e- were found to significantly vary as a function of the altitude along the field line and, independently, as a function of time. In this follow-up study, we employ the same approach to study a sample of the recently discovered Europa- and Ganymede-Jupiter decametric emissions, as observed from the Nançay Decameter Array (NDA) and NenuFAR in Nançay. Interestingly, we measure θ and E_e- which strikingly compare to those obtained for the Io-Jupiter decametric events, promoting common acceleration and radio emission processes for the three planet-moon interactions.