Similar LF/VLF Radio Emissions Observed at Jupiter and Saturn

Both Jupiter and Saturn emit various kinds of nonthermal radio emissions into interplanetary space. These emissions can provide important information on the plasma environment of their source region and on the magnetospheric dynamics of the planet. It is well known that the auroral cyclotron maser emissions dominate the radio spectra observed at both planets. In the low frequency (LF) and the very low frequency (VLF) range, similar narrowbanded features are also observed at both planets. At Saturn, narrowband emissions are observed between 3 and 70 kHz, with occurrence probability and wave intensity peaking around 5 kHz and 20 kHz. At Jupiter, narrowband emissions are observed at higher frequencies, with the narrowband kilometric radiation (nKOM) observed around 100 kHz and the escaping continuum around 10 kHz. In this paper, we present Cassini RPWS observations of Jovian nKOM and escaping continuum radiation and discuss the similarities between them and the Saturn narrowband emissions. For example, all these emissions are modulated at the rotation period of the planets. The nKOM is a rotating beam whereas the 5 kHz Saturn narrowband emission and the Jovian escaping continuum behave like a flashing light. Their polarizations are also similar. The nKOM and the 20 kHz Saturn narrowband emissions are both highly circularly polarized in the sense of L-O mode emission. The Jovian escaping continuum and the 5 kHz Saturn narrowband emissions are mostly unpolarized when they are observed at low latitudes. Previous studies on the Jupiter low frequency radio emissions can help us understand the source mechanism of the Saturn narrowband emissions.