Lewis, Z M; Beth, A; Altwegg, K; Galand, M; Goetz, C; Heritier, K; O’Rourke, L; Rubin, M; Stephenson, P (2023). Origin and trends in NH4+ observed in the coma of 67P. Monthly notices of the Royal Astronomical Society, 523(4), pp. 6208-6219. Oxford University Press 10.1093/mnras/stad1787
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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.
Item Type: |
Journal Article (Original Article) |
|---|---|
Division/Institute: |
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences 08 Faculty of Science > Physics Institute |
UniBE Contributor: |
Altwegg, Kathrin, Rubin, Martin |
Subjects: |
500 Science > 520 Astronomy 500 Science > 530 Physics 600 Technology > 620 Engineering |
ISSN: |
0035-8711 |
Publisher: |
Oxford University Press |
Language: |
English |
Submitter: |
Dora Ursula Zimmerer |
Date Deposited: |
27 Oct 2023 07:13 |
Last Modified: |
27 Oct 2023 07:13 |
Publisher DOI: |
10.1093/mnras/stad1787 |
BORIS DOI: |
10.48350/187475 |
URI: |
https://boris.unibe.ch/id/eprint/187475 |
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