Abstract
By analysing a database of 26 yr of observations of Jupiter with the Nançay Decameter Array, we unambiguously identify the radio emissions caused by the Ganymede–Jupiter interaction. We study the energetics of these emissions via the distributions of their intensities, duration, and power, and compare them to the energetics of the Io–Jupiter radio emissions. This allows us to demonstrate that the average emitted radio power is proportional to the Poynting flux from the rotating Jupiter’s magnetosphere intercepted by the obstacle. We then generalize this result to the radio-magnetic scaling law that appears to apply to all plasma interactions between a magnetized flow and an obstacle, magnetized or not. Extrapolating this scaling law to the parameter range corresponding to hot Jupiters, we predict large radio powers emitted by these objects, that should result in detectable radio flux with new-generation radiotelescopes. Comparing the distributions of the durations of Ganymede–Jupiter and Io–Jupiter emission events also suggests that while the latter results from quasi-permanent Alfvén wave excitation by Io, the former likely results from sporadic reconnection between magnetic fields Ganymede and Jupiter, controlled by Jupiter’s magnetic field geometry and modulated by its rotation.
Highlights
4000 exoplanets have been discovered in the past two decades1, but little is known yet on their interior and their rotation
The non-Io emissions, which include auroral radio emissions as well as emissions possibly caused by satellites other than Io, display time–frequency shapes and polarizations that can be classified in A, B, C, and D categories similar to I–J ones
A first analysis showed that no emission event with frequency >33 MHz is detected in regions of enhanced probability in the central meridian longitude (CML)−ΦGa plane for non-Io-A and non-Io-B emissions
Summary
4000 exoplanets have been discovered in the past two decades, but little is known yet on their interior and their rotation. 4, we combine the results obtained for I–J and G–J emissions to the scaling laws relating radio powers to incident kinetic or magnetic energy fluxes, and we show that the radio-magnetic scaling law provides a general frame for all radio emissions resulting from a flow– obstacle interaction. We extrapolate this scaling law to the hot Jupiters regime and predict radio powers – and flux densities – 103−7 times stronger than Jupiter’s.
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