TY - JOUR
T1 - Solar wind charge exchange in cometary atmospheres: III. Results from the Rosetta mission to comet 67P/Churyumov-Gerasimenko
AU - Wedlund, Cyril Simon
AU - Behar, Etienne
AU - Nilsson, Hans
AU - Alho, Markku
AU - Kallio, Esa
AU - Gunell, Herbert
AU - Bodewits, Dennis
AU - Heritier, Kevin
AU - Galand, Marina
AU - Beth, Arnaud
AU - Rubin, Martin
AU - Altwegg, Kathrin
AU - Volwerk, Martin
AU - Gronoff, Guillaume
AU - Hoekstra, Ronnie
N1 - Funding Information:
cA knolw edgements. The work at the University of Oslo was funded by the Norwegian Research Council grant No. 240000. Work at the Royal Belgian Institute for Space Aeronomy was supported by the Belgian Science Policy Office through the Solar-Terrestrial Centre of Excellence. Work at Umeå University was funded by SNSB grant 201/15 and SNSA grant 108/18. The work at NASA/SSAI was supported by NASA Astrobiology Institute grant NNX15AE05G and by the NASA HIDEE Program. Work at Imperial College London was supported by STFC of UK under grant ST/N000692/1 and by ESA under contract No. 4000119035/16/ES/JD. The authors thank the ISSI International Team “Plasma Environment of comet 67P after Rosetta” for fruitful discussions and collaborations. C.S.W. thanks M.S.W. for inspiring discussions and ideas to improve the manuscript and figures. Datasets of the Rosetta mission can be freely accessed from ESA’s Planetary Science Archive (http://archives.esac.esa.int/ psa).
Publisher Copyright:
© ESO 2019.
PY - 2019/10/1
Y1 - 2019/10/1
N2 - Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary. Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas. Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions. Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.
AB - Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary. Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas. Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions. Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.
KW - Comets: General
KW - comets: individual: 67P / Churyumov-Gerasimenko
KW - instrumentation: detectors
KW - solar wind, methods: analytical
KW - solar wind: charge-exchange processes
UR - http://www.scopus.com/inward/record.url?scp=85103742363&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201834881
DO - 10.1051/0004-6361/201834881
M3 - Article
SN - 0004-6361
VL - 630
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
M1 - A37
ER -