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Solar Wind Protons forming Partial Ring Distributions at Comet 67P
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  • Anja Moeslinger,
  • Gabriella Stenberg Wieser,
  • Hans Nilsson,
  • Herbert Gunell,
  • Hayley N. Williamson,
  • Kristie LLera,
  • Elias Odelstad,
  • Ingo Richter
Anja Moeslinger
Swedish Institute of Space Physics

Corresponding Author:[email protected]

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Gabriella Stenberg Wieser
Swedish Institute of Space Physics
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Hans Nilsson
Swedish Institute of Space Physics
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Herbert Gunell
Umeå University
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Hayley N. Williamson
Swedish Institute of Space Physics
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Kristie LLera
Southwest Research Institute
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Elias Odelstad
Swedish Institute of Space Physics
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Ingo Richter
Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig
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Abstract

We present partial ring distributions of solar wind protons observed by the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. The formation of ring distributions is usually associated with high activity comets, where the spatial scales are larger than multiple ion gyroradii. Our observations are made at a low-activity comet at a heliocentric distance of 2.8 AU on April 19th, 2016, and the partial rings occur at a spatial scale comparable to the ion gyroradius. We use a new visualisation method to simultaneously show the angular distribution of median energy and differential flux. A fitting procedure extracts the bulk speed of the solar wind protons, separated into components parallel and perpendicular to the gyration plane, as well as the gyration velocity. The results are compared with models and put into context of the global comet environment. We find that the formation mechanism of these partial rings of solar wind protons is entirely different from the well-known partial rings of cometary pickup ions at high-activity comets. A density enhancement layer of solar wind protons around the comet is a focal point for proton trajectories originating from different regions of the upstream solar wind. If the spacecraft location coincides with this density enhancement layer, the different trajectories are observed as an energy-angle dispersion and manifest as partial rings in velocity space.