Ion and Electron Sensor Observations on Photoelectrons and Coma Development at Comet 67P/Churyumov-Gerasimenko

Thursday, 18 December 2014
James L Burch1, Raymond Goldstein1, Pat Mokashi1, Craig J Pollock2, Tom Broiles1, Kathleen Mandt1, Thomas Cravens3, Marilia Samara2, Anders I Eriksson4, Chris Carr5, Jean-Pierre Lebreton6, Pierre Henri6, Karl-Heinz Glassmeier7, Hans Nilsson8 and Christoph Koenders7, (1)Southwest Research Institute, San Antonio, TX, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)University of Kansas, Lawrence, KS, United States, (4)IRF Swedish Institute of Space Physics Uppsala, Uppsala, Sweden, (5)Imperial College London, London, United Kingdom, (6)Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Orléans Cedex 2, France, (7)Technical University of Braunschweig, Braunschweig, Germany, (8)IRF Swedish Institute of Space Physics Kiruna, Kiruna, Sweden
The Ion and Electron Sensor (IES) on Rosetta measures 3D fluxes of electrons and total ions over an energy/charge range from 4 eV to 30 keV. The field of view is swept electrostatically over 2.8 pi steradians with energy resolution of 4% and angular resolution of 5 x 22.5 deg. for electrons and 5 x 45 deg. for ions except over the 45-deg. sector that typically views the solar wind, within which the resolution is 5 x 5 deg. As Rosetta approached to and within 100 km of the comet, enhanced fluxes of electrons were observed at energies below a few hundred eV. In one case on Aug. 2, 2014, the enhanced fluxes were observed during a time when the comet activity (gas and/or dust ejections) was observed by the multispectral imager (OSIRIS), suggesting the start of coma development. In another instance on Aug. 7, 2014, a large enhancement of electron fluxes was at energies in the tens of eV range, indicative of possible photoelectrons emitted from the nucleus. These, and expected subsequent observations, are described in this paper.