title: Detection of a strongly negative surface potential at Saturn's moon Hyperion.
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.
authors.affiliation: Mullard Space Science Laboratory, University College London Dorking, UK ; Centre for Planetary Sciences at UCL/Birkbeck London, UK.
authors.forename: T A
authors.initials: TA
authors.lastname: Nordheim
authors.affiliation: Mullard Space Science Laboratory, University College London Dorking, UK ; Centre for Planetary Sciences at UCL/Birkbeck London, UK.
authors.forename: G H
authors.initials: GH
authors.lastname: Jones
authors.affiliation: Max Planck Institute for Solar System Research Göttingen, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Roussos
authors.affiliation: Institute for Theoretical Physics, Braunschweig University of Technology Braunschweig, Germany ; Now at SDSE, LLC Silver Spring, Maryland, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Leisner
authors.affiliation: Mullard Space Science Laboratory, University College London Dorking, UK ; Centre for Planetary Sciences at UCL/Birkbeck London, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Coates
authors.affiliation: Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA.
authors.forename: W S
authors.initials: WS
authors.lastname: Kurth
authors.affiliation: Institute of Geophysics and Planetary Physics, University of California Los Angeles, California, USA.
authors.forename: K K
authors.initials: KK
authors.lastname: Khurana
authors.affiliation: Max Planck Institute for Solar System Research Göttingen, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Krupp
authors.affiliation: Blackett Laboratory, Imperial College London London, UK.
authors.forename: M K
authors.initials: MK
authors.lastname: Dougherty
authors.affiliation: Southwest Research Institute San Antonio, Texas, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Waite
keywords: Cassini; Hyperion; Saturn's moons; surface charging