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ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet
SW Res Inst, Div Space Sci, San Antonio, TX 78228 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
Univ Bern, Inst Phys, CH-3012 Bern, Switzerland..
Univ Bern, Inst Phys, CH-3012 Bern, Switzerland..
LATMOS, F-94100 St Maur, France..
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2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, A2Article in journal (Refereed) PublishedText
Abstract [en]

Context. The Rosetta encounter with comet 67P/Churyumov-Gerasimenko provides a unique opportunity for an in situ, up-close investigation of ion-neutral chemistry in the coma of a weakly outgassing comet far from the Sun. Aims. Observations of primary and secondary ions and modeling are used to investigate the role of ion-neutral chemistry within the thin coma. Methods. Observations from late October through mid-December 2014 show the continuous presence of the solar wind 30 km from the comet nucleus. These and other observations indicate that there is no contact surface and the solar wind has direct access to the nucleus. On several occasions during this time period, the Rosetta/ROSINA/Double Focusing Mass Spectrometer measured the low-energy ion composition in the coma. Organic volatiles and water group ions and their breakup products (masses 14 through 19), COP, and CO, (masses 28 and 44) and other mass peaks (at masses 26, 27, and possibly 30) were observed. Secondary ions include H3O+ and HCO+ (masses 19 and 29). These secondary ions indicate ion-neutral chemistry in the thin coma of the comet. A relatively simple model is constructed to account for the low H3O /H2O+ and HCO /CO+ ratios observed in a water dominated coma. Results from this simple model are compared with results from models that include a more detailed chemical reaction network. Results. At low outgassing rates, predictions from the simple model agree with observations and with results from more complex models that include much more chemistry. At higher outgassing rates, the ion-neutral chemistry is still limited and high HCO /CO+ ratios are predicted and observed. However, at higher outgassing rates, the model predicts high H3O /H2O+ ratios and the observed ratios are often low. These low ratios may be the result of the highly heterogeneous nature of the coma, where CO and CO2 number densities can exceed that of water.

Place, publisher, year, edition, pages
2015. Vol. 583, A2
Keyword [en]
comets: individual: 67P/Churyumov-Gerasimenko, solar wind, plasmas, molecular processes, methods: data analysis
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-270603DOI: 10.1051/0004-6361/201526210ISI: 000365072200070OAI: oai:DiVA.org:uu-270603DiVA: diva2:890260
Swedish National Space Board
Available from: 2016-01-01 Created: 2016-01-01 Last updated: 2016-01-01Bibliographically approved

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Vigren, Erik
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Swedish Institute of Space Physics, Uppsala Division
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