Juno Reveals New Insights Into Io-Related Decameter Radio Emissions

The Juno mission is providing stunning new information about Jupiter and its environment. A new magnetic field model (JRM09) with much improved accuracy near the planet provides the basis for a better understanding of Io-related decametric radio emissions (DAM) and implications for auroral processes. Here, we selected Io-related DAM events observed by the Juno Waves instrument to shed light into the beaming angle, the resonant electron energy, and radio source location by forward modeling. We use the JRM09 model to better constrain the location and observability of DAM and characterize the loss cone-driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs with calculated beaming angles ranging from 33° to 85° and resonant electron energies up to 23 times higher than previously proposed. In addition, through a quantitative analysis, we provide an explanation regarding the higher likelihood of observing groups of arcs of Io DAM originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator.