Detection of a strongly negative surface potential at Saturn's moon Hyperion
Coates, A. J.; Krupp, N.; Dougherty, M. K.; Jones, G. H.; Roussos, E.; Khurana, K. K.; Kurth, W. S.; Waite, J. H.; Leisner, J. S.; Nordheim, T. A.
United Kingdom, Germany, United States
Abstract
On 26 September 2005, Cassini conducted its only close targeted flyby of Saturn's small, irregularly shaped moon Hyperion. Approximately 6 min before the closest approach, the electron spectrometer (ELS), part of the Cassini Plasma Spectrometer (CAPS) detected a field-aligned electron population originating from the direction of the moon's surface. Plasma wave activity detected by the Radio and Plasma Wave instrument suggests electron beam activity. A dropout in energetic electrons was observed by both CAPS-ELS and the Magnetospheric Imaging Instrument Low-Energy Magnetospheric Measurement System, indicating that the moon and the spacecraft were magnetically connected when the field-aligned electron population was observed. We show that this constitutes a remote detection of a strongly negative (~ -200 V) surface potential on Hyperion, consistent with the predicted surface potential in regions near the solar terminator.