Open AccessFlow directions of low-energy ions in and around the diamagnetic cavity of comet 67P
Author(s) -
Sofia Bergman,
Gabriella Stenberg Wieser,
Martin Wieser,
Hans Nilsson,
Erik Vigren,
Arnaud Beth,
Kei Masunaga,
Anders Eriksson
Publication year - 2021
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1093/mnras/stab2470
Subject(s) - comet , physics , ion , diamagnetism , spacecraft , atomic physics , solar wind , plasma , astrophysics , astronomy , magnetic field , nuclear physics , quantum mechanics
The flow direction of low-energy ions around comet 67P/Churyumov–Gerasimenko has previously been difficult to constrain due to the influence of the spacecraft potential. The Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA) on Rosetta measured the distribution function of positive ions with energies down to just a few eV/q throughout the escort phase of the mission. Unfortunately, the substantial negative spacecraft potential distorted the directional information of the low-energy data. In this work, we present the flow directions of low-energy ions around comet 67P, corrected for the spacecraft potential using Particle-In-Cell simulation results. We focus on the region in and around the diamagnetic cavity, where low-energy ions are especially important for the dynamics. We separate between slightly accelerated ‘burst’ features and a more constant ‘band’ of low-energy ions visible in the data. The ‘bursts’ are flowing radially outwards from the nucleus with an antisunward component while the ‘band’ is predominantly streaming back towards the comet. This provides evidence of counter-streaming ions, which has implications for the overall expansion velocity of the ions. The backstreaming ions are present also at times when the diamagnetic cavity was not detected, indicating that the process accelerating the ions back towards the comet is not connected to the cavity boundary.