Observations of Modulation of Ion flux in the Coma of Comet
67P/Churyumov-Gerasimenko
Abstract
In early June 2015 the Ion and Electron Sensor (IES) on board the
Rosetta spacecraft (SC) observed troughs in the ion measurements at
about 200 km from the comet. The troughs coincided with measurement
results of two other instruments on board Rosetta: the peaks of the
neutral gas density measured by the Rosetta Orbiter Spectrometer for Ion
and Neutral Analysis (ROSINA) and the peaks of the electron density
measured by the Langmuir and Mutual Impedence Probe Instruments, (LAP
and MIP) and the most negative levels of the Spacecraft potential also
measured by LAP. We propose that the dips in the ion measurements are
the result of charge exchange reactions between the ions and the neutral
population emitted by the comet nucleus. Measurements from the Ion
Composition Analyzer (ICA) on board Rosetta show that these ions are
mostly water ions.