@article{Lewis:2023:mnras/stad1787,
author = {Lewis, ZM and Beth, A and Altwegg, K and Galand, M and Goetz, C and Heritier, K and ORourke, L and Rubin, M and Stephenson, P},
doi = {mnras/stad1787},
journal = {Monthly Notices of the Royal Astronomical Society},
pages = {6208--6219},
title = {Origin and trends in NH4+ observed in the coma of 67P},
url = {http://dx.doi.org/10.1093/mnras/stad1787},
volume = {523},
year = {2023}
}

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TY  - JOUR
AB  - The European Space Agency/Rosetta mission escorted comet 67P/Churyumov–Gerasimenko and witnessed the evolution of its coma from low activity (∼2.5–3.8 au) to rich ion-neutral chemistry (∼1.2–2.0 au). We present an analysis of the ion composition in the coma, focusing on the presence of protonated high proton affinity (HPA) species, in particular NH4+. This ion is produced through the protonation of NH3 and is an indicator of the level of ion-neutral chemistry in the coma. We aim to assess the importance of this process compared with other NH4+ sources, such as the dissociation of ammonium salts embedded in dust grains. The analysis of NH4+ has been possible thanks to the high mass resolution of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Double Focusing Mass Spectrometer (ROSINA/DFMS). In this work, we examine the NH4+ data set alongside data from the Rosetta Plasma Consortium instruments, and against outputs from our in-house ionospheric model. We show that increased comet outgassing around perihelion yields more detections of NH4+ and other protonated HPA species, which results from more complex ion-neutral chemistry occurring in the coma. We also reveal a link between the low magnetic field strength associated with the diamagnetic cavity and higher NH4+ counts. This suggests that transport inside and outside the diamagnetic cavity is very different, which is consistent with 3D hybrid simulations of the coma: non-radial plasma dynamics outside the diamagnetic cavity is an important factor affecting the ion composition.
AU  - Lewis,ZM
AU  - Beth,A
AU  - Altwegg,K
AU  - Galand,M
AU  - Goetz,C
AU  - Heritier,K
AU  - ORourke,L
AU  - Rubin,M
AU  - Stephenson,P
DO  - mnras/stad1787
EP  - 6219
PY  - 2023///
SN  - 0035-8711
SP  - 6208
TI  - Origin and trends in NH4+ observed in the coma of 67P
T2  - Monthly Notices of the Royal Astronomical Society
UR  - http://dx.doi.org/10.1093/mnras/stad1787
UR  - https://academic.oup.com/mnras/article/523/4/6208/7198117?
UR  - http://hdl.handle.net/10044/1/105248
VL  - 523
ER  - 

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