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An experimental study of the mixing of CO₂ and N₂ under conditions found at the surface of Venus

Lebonnois, Sébastien and Schubert, Gerald and Kremic, Tibor and Nakley, Leah M. and Phillips, Kyle G. and Bellan, Josette and Cordier, Daniel (2020) An experimental study of the mixing of CO₂ and N₂ under conditions found at the surface of Venus. Icarus, 338 . Art. No. 113550. ISSN 0019-1035.

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Based on the only reliable temperature profile available in the deepest ∼10 km layer above Venus’ surface (obtained by the VeGa-2 landing probe), the mixing conditions of the main constituents of Venus’s atmosphere, CO₂ and N₂, have been questioned. In this work, we report the results of a series of experiments that were done in the GEER facility at Glenn Research Center to investigate the homogeneity of CO₂/N₂ gas mixtures at 100 bars and temperatures ranging from ∼296 K to ∼735 K. When the gas mixtures are initially well-mixed, separation of the two gases based on their molecular mass does not occur over the time scales observed; although, small systematic variations in composition remain to be fully interpreted. However, when N₂ is injected on top of CO₂ (layered fill), the very large density ratio makes it more difficult to mix the two chemical species. Timescales of mixing are of the order of 10² hours over the height of the test vessel (roughly 60 cm), and even longer when the gas mixture is at rest and only molecular diffusion is occurring. At room temperature, close to the critical point of the mixture, large pressure variations are obtained for the layered fill, as N₂ slowly mixes into CO₂. This can be explained by large density variations induced by the mixing. For conditions relevant to the near-surface atmosphere of Venus, separation of CO₂ and N₂ based on their molecular mass and due to physical properties of the gas mixture is not demonstrated, but can not be firmly excluded either. This suggests that if the compositional vertical gradient deduced from the VeGa-2 temperature profile is to be trusted, it would most probably be due to some extrinsic processes (not related to gas properties, e.g. CO₂ volcanic inputs) and large mixing time constants.

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Bellan, Josette0000-0001-9218-7017
Additional Information:© 2019 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. Received 30 April 2019, Revised 5 September 2019, Accepted 11 November 2019, Available online 23 November 2019. This work was funded by the NASA Solar System Workings Program, grant 80NSSC17K0774. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Subject Keywords:Super-critical fluid; Venus; Atmosphere; Composition; CO2/N2 mixtures; VeGa-2 temperature profile
Record Number:CaltechAUTHORS:20191127-092423364
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Official Citation:Sébastien Lebonnois, Gerald Schubert, Tibor Kremic, Leah M. Nakley, Kyle G. Phillips, Josette Bellan, Daniel Cordier, An experimental study of the mixing of CO2 and N2 under conditions found at the surface of Venus, Icarus, Volume 338, 2020, 113550, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100092
Deposited By: Tony Diaz
Deposited On:27 Nov 2019 18:24
Last Modified:10 Dec 2019 20:55

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