PhD defense by Brieuc Collet :Understanding the microphysics of Jupiter’s auroral radio emissions with Juno.

September 22, 2025, at 2 p.m. in the amphitheater of the Marseille Astrophysics Laboratory. The defense will be in French, but the supporting presentation will be in English.

Jupiter is the most intense source of auroral radio emissions in the Solar System. These emissions are emitted perpendicular to the magnetic field in a hollow cone at a frequency close to the cyclotron frequency.
These emissions have been observed and characterized by ground- and space-based observations and are now divided into four categories: the decametric emissions (DAM), including those induced by the Galilean moons (Moon-DAM), the hectometric emissions (HOM), and the broadband kilometer emissions (bKOM). They are produced in the polar regions of Jupiter’s magnetosphere, a unique laboratory due to its size and internal processes. These emissions are generated by a wave-plasma instability: the Cyclotron Maser Instability (CMI). It requires a depleted and magnetized plasma and an electronic population inversion.

The aim of this thesis is to confirm CMI as the generation mechanism for Jovian auroral radio emissions.
To do this, I use in situ radio, plasma, and magnetic measurements from Juno, the first polar orbiter to cross Jupiter’s auroral regions.
From radio spectra, I have compiled a catalog of candidate radio source crossings, which were then confirmed by a growth rate analysis based on Juno’s electron measurements and a new expression of the growth rate.
I found that HOM and DAM sources were generated mainly by electron distributions showing a loss cone, and marginally by conics, and shells which I identified for the first time at Jupiter.
The bKOM sources were produced by conics and shells, and can be located in auroral cavities reminiscent of those observed in Earth’s radio auroral emissions source regions.
These results confirm the universality of CMI for the generation of auroral radio emissions and could be applied to other magnetized planets.