Enceladus auroral hiss observations: Implications for electron beam locations

摘要

The Cassini spacecraft has made 20 close flybys of the icy moon Enceladus between its arrival at Saturn in 2004 and 2012. Of those 20, strong whistler mode emissions (often called auroral hiss) were clearly observed on seven encounters. The propagation paths of these emissions are determined by the background magnetic field, which allows their source regions to be studied using simple ray-tracing codes. In this paper, we trace the auroral hiss observations from Cassini's trajectories to possible source locations near Enceladus. We find that all of the detected emissions could be generated by field-aligned electron beams in one of two regions around the moon: upstream of the Saturnward terminator and downstream of the anti-Saturnward terminator. These results suggest that electron beam acceleration near the solid body is a quasi-time-stationary feature of the plasma interaction and that the auroral hiss generated by these beams may be used to remotely study plasma processes in regions separated from the spacecraft.