Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA

Hans Nilsson, Gabriella Stenberg Wieser, Etienne Behar, Herbert Gunell, Martin Wieser, Marina Galand, Cyril Simon Wedlund, Markku Alho, Charlotte Goetz, Masatoshi Yamauchi, Pierre Henri, Elias Odelstad, Erik Vigren

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Abstract

Rosetta has followed comet 67P from low activity at more than 3.6 au heliocentric distance to high activity at perihelion (1.24 au) and then out again. We provide a general overview of the evolution of the dynamic ion environment using data from the RPC-ICA ion spectrometer. We discuss where Rosetta was located within the evolving comet magnetosphere. For the initial observations, the solar wind permeated all of the coma. In 2015 mid-April, the solar wind started to disappear from the observation region, to re-appear again in 2015 December. Low-energy cometary ions were seen at first when Rosetta was about 100 km from the nucleus at 3.6 au, and soon after consistently throughout the mission except during the excursions to farther distances from the comet. The observed flux of low-energy ions was relatively constant due to Rosetta's orbit changing with comet activity. Accelerated cometary ions, moving mainly in the antisunward direction gradually became more common as comet activity increased. These accelerated cometary ions kept being observed also after the solar wind disappeared from the location of Rosetta, with somewhat higher fluxes further away from the nucleus. Around perihelion, when Rosetta was relatively deep within the comet magnetosphere, the fluxes of accelerated cometary ions decreased, as did their maximum energy. The disappearance of more energetic cometary ions at close distance during high activity is suggested to be due to a flow pattern where these ions flow around the obstacle of the denser coma or due to charge exchange losses.
Original languageEnglish
Pages (from-to)S252–S261
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume469
Issue numberSuppl
DOIs
Publication statusPublished - 2017
MoE publication typeA1 Journal article-refereed

Keywords

  • plasmas
  • methods: data analysis
  • comets: individual: 67P

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