Direct Simulation Monte Carlo modelling of the major species in the coma of comet 67P/Churyumov-Gerasimenko

Fougere, Nicolas; Altwegg, Kathrin; Berthelier, J.-J.; Bieler, André; Bockelée-Morvan, D.; Calmonte, Ursina Maria; Capaccioni, F.; Combi, M. R.; De Keyser, J.; Debout, V.; Erard, S.; Fiethe, B.; Filacchione, G.; Fink, U.; Fuselier, S. A.; Gombosi, T. I.; Hansen, K. C.; Hässig, Myrtha; Huang, Z.; Le Roy, L.; ... (2016). Direct Simulation Monte Carlo modelling of the major species in the coma of comet 67P/Churyumov-Gerasimenko. Monthly notices of the Royal Astronomical Society, 462(Suppl 1), S156-S169. Oxford University Press 10.1093/mnras/stw2388

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We analyse the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) – the Double Focusing Mass Spectrometer data between 2014 August and 2016 February to examine the effect of seasonal variations on the four major species within the coma of 67P/ChuryumovGerasimenko (H₂O, CO₂, CO, and O₂), resulting from the tilt in the orientation of the comet’s spin axis. Using a numerical data inversion, we derive the non-uniform activity Distribution at the surface of the nucleus for these species, suggesting that the activity distribution at the surface of the nucleus has not significantly been changed and that the differences observed in the coma are solely due to the variations in illumination conditions. A three-dimensional Direct Simulation Monte Carlo model is applied where the boundary conditions are computed with a coupling of the surface activity distributions and the local illumination. The model is able to reproduce the evolution of the densities observed by ROSINA including the changes happening at equinox. While O₂ stays correlated with H₂O as it was before equinox, CO₂ and CO, which had a poor correlation with respect to H₂O pre-equinox, also became well correlated with H₂O post-equinox. The integration of the densities from the model along the line of sight results in column densities directly comparable to the VIRTIS-H observations. Also, the evolution of the volatiles’ production rates is derived from the coma model showing a steepening in the production rate curves after equinox. The model/data comparison suggests that the seasonal effects result in the Northern hemisphere of 67P’s nucleus being more processed with a layered structure while the Southern hemisphere constantly exposes new material.

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; Bieler, André; Calmonte, Ursina Maria; Hässig, Myrtha; Rubin, Martin and Tzou, Chia-Yu

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

0035-8711

Publisher:

Oxford University Press

Language:

English

Submitter:

Katharina Weyeneth-Moser

Date Deposited:

06 Jul 2017 10:12

Last Modified:

06 Jul 2017 10:12

Publisher DOI:

10.1093/mnras/stw2388

BORIS DOI:

10.7892/boris.97007

URI:

https://boris.unibe.ch/id/eprint/97007

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