Observed deviations from the typical, plasma-absorbing interaction region profile may explain some differences. These deviations do not necessarily mean the main interaction mode at Rhea is not plasma absorption. For instance, Simon et al. (2012) demonstrates that the combination of low magnetosonic Mach number and the high plasma beta values of Rhea’s space environment amplifies interaction features which for other plasma absorbers (e.g. Tethys, Dione, Earth’s Moon) are barely detectable. One of these features is a stronger, flow-aligned magnetic field component perturbation, which gives rise to mass-loading-like interaction signatures. Such structures may also complicate electron drifts, but to what extent it is uncertain. Similarly, the high plasma beta makes surface charging more important for Rhea compared to the other Saturnian moons (Roussos et al., 2010). Furthermore, recent developments in the study of Earth’s Moon interaction with the solar wind indicate that the standard picture for a lunar-type interaction may be too simplified: processes, such as the entry of exospheric pick-up ions in the center of the wake, backscattering on the surface and self-pick up of ambient plasma ions, appear to also have an impact on the wake dynamics (Halekas et al., 2011). For instance, the self-pick up process has been shown to lead to enhanced ULF wave activity in the lunar, at least 10% of the time (Nakagawa et al., 2012). Whether a similar process is important the inferred instability at Rhea is questionable, as the latter appears to operate continuously.
features
One
enhanced ULF wave activity in the lunar
self-pick up process has been shown to lead to
at least 10%
%