@article{822e3c0d0a10474a936b7b503fd7f30f,
title = "Direct Simulation Monte Carlo modelling of the major species in the coma of comet 67P/Churyumov-Gerasimenko",
abstract = "We analyse the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) - the Double FocusingMass 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/Churyumov- Gerasimenko (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.Athree-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 ROSINAincluding 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.",
keywords = "Comets: general, Comets: individual: 67P/Churyumov-Gerasimenko, Space vehicles, Space vehicles: instruments",
author = "{the VIRTIS and the ROSINA teams} and Nicolas Fougere and K. Altwegg and Berthelier, {J. J.} and A. Bieler and D. Bockel{\'e}e-Morvan and U. Calmonte and F. Capaccioni and {R. Combi}, M. and {De Keyser}, J. and V. Debout and S. Erard and B. Fiethe and G. Filacchione and U. Fink and Fuselier, {S. A.} and Gombosi, {T. I.} and Hansen, {K. C.} and M. H{\"a}ssig and Z. Huang and {Le Roy}, L. and C. Leyrat and A. Migliorini and G. Piccioni and G. Rinaldi and M. Rubin and Y. Shou and V. Tenishev and G. Toth and Tzou, {C. Y.}",
note = "Funding Information: This work was supported by contracts JPL1266313 and JPL 1266314 from the US Rosetta Project and NASA grant NNX14AG84G from the Planetary Atmospheres Program. Work at UoB was funded by the State of Bern, the Swiss National Science Foundation, and the European Space Agency PRODEX Program. Work at Southwest Research institute was supported by subcontract 1496541 from the Jet Propulsion Laboratory. Work at BIRA-IASB was supported by the Belgian Science Policy Office via PRODEX/ROSINA PEA C4000107705 and an Additional Researchers Grant (Ministerial Decree of 2014-12-19), as well as by the Fonds de la Recherche Scientifique grant PDR T.1073.14 'Comparative study of atmospheric erosion'. ROSINA would not give such outstanding results without the work of the many engineers, technicians, and scientists involved in the mission, in the Rosetta spacecraft, and in the ROSINAinstrument team over the last 20 years whose contributions are gratefully acknowledged. The authorswould like to thank ASI, Italy; CNES, France; DLR, Germany; and NASA, USA for supporting this research. VIRTIS was built by a consortium formed by Italy, France, and Germany under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Italy, which also guides the scientific operations. The consortium also includes the Laboratoire d'?tudes spatiales et d'instrumentation en astrophysique of the Observatoire de Paris, France, and the Institut f?r Planetenforschung of DLR, Germany. The authors wish to thank the Rosetta Science Ground Segment and the Rosetta Mission Operations Centre for their continuous support. The authors thank the NASA Supercomputer Division at AMES for enabling them to perform the simulations presented in this paper on Pleiades supercomputers. Publisher Copyright: {\textcopyright} 2017 The Authors.",
year = "2016",
doi = "10.1093/mnras/stw2388",
language = "English (US)",
volume = "462",
pages = "S156--S169",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
}