The generation of whistler-mode waves and their interactions with energetic electrons in Jupiter’s polar regions, including applications beyond the giant planet

Abstract:

Jupiter is an ideal laboratory for understanding fundamental plasma physics processes not only because Jupiter’s aurora is the most powerful in the solar system, but because the Jovian polar regions are home to a plethora of wave-particle interactions and associated auroral activity. Juno is the first mission to pass directly over the low altitude polar and auroral regions of Jupiter, making observations in regions where particle acceleration is present and radio and plasma wave emissions are known to be generated. The Juno spacecraft observed intense broadband upward-propagating whistler-mode waves associated with upward-traveling energetic electrons over the entire Jovian polar region. Whistler-mode auroral hiss is known to be generated by electron beams via an instability at the Landau resonance. We discuss the mechanisms by which the waves are produced and how they interact with the electrons by altering their energies and pitch angles. The interaction begins with a downward field-aligned current over the polar cap, resulting in strong downward parallel electric fields and upward-traveling electron beams. The beams then produce broadband upward-traveling whistler-mode auroral hiss by a beam-plasma instability at the Landau resonance. As the waves propagate upwards, their phase velocity increases, which has the potential to carry trapped electrons to high energies. We show evidence that they participate in pitch angle scattering and acceleration of resonant electrons. Numerical calculations of wave growth rates show that electron beams can produce the observed wave intensities. This study brings a new understanding of fundamental physics processes that are common to all planetary systems with strong magnetic fields. We also discuss how this physics is applicable to other areas of the heliosphere, such as wave-particle interactions in the solar wind.