The Rosetta Ion and Electron Sensor (IES) Measurement of the Development of Pickup Ions from Comet 67P/Churyumov-Gerasimenko
Thursday, 18 December 2014
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 20 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. IES is part of the 5 instrument Rosetta Plasma Consortium (RPC). IES has been measuring solar wind ions intermittently (because of S/C pointing issues) since exiting from hibernation in May 2014. On August 5, when Rosetta was ~160 km from comet 67P, IES began to see ions at its upper energy range, ~20 keV. We identify these energetic ions as ions created from neutral species emitted by the comet nucleus, photoionized by solar UV radiation and then "picked up" by the interplanetary magnetic field (IMF). These picked up ions were seen intermittently until abstract submission time on August 7, while also measuring solar wind protons at ~600 eV. The solar wind, as expected, was from the direction of the sun, whereas the energetic ions were away from the solar direction. This is also expected for pickup ions. IES continued to follow changes in the solar wind and the development of the pickup ion structure, which will be reported in this paper.