Properties of Saturn kilometric radiation measured within its source region
Schippers, P.; André, N.; Gurnett, D. A.; Coates, A. J.; Dougherty, M. K.; Kurth, W. S.; Cecconi, B.; Lamy, L.; Louarn, P.; Zarka, P.; Arridge, C. S.; Mutel, R. L.
United Kingdom, United States, France
Abstract
On 17 October 2008, the Cassini spacecraft crossed the southern sources of Saturn kilometric radiation (SKR), while flying along high-latitude nightside magnetic field lines. In situ measurements allowed us to characterize for the first time the source region of an extra-terrestrial auroral radio emission. Using radio, magnetic field and particle observations, we show that SKR sources are surrounded by a hot tenuous plasma, in a region of upward field-aligned currents. Magnetic field lines supporting radio sources map a continuous, high-latitude and spiral-shaped auroral oval observed on the dawnside, consistent with enhanced auroral activity. Investigating the Cyclotron Maser Instability (CMI) as a mechanism responsible for SKR generation, we find that observed cutoff frequencies are consistent with radio waves amplified perpendicular to the magnetic field by hot (6 to 9 keV) resonant electrons, measured locally.