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Low levels of sulphur dioxide contamination of Venusian phosphine spectra

Greaves, Jane S ORCID:, Rimmer, Paul B, Richards, Anita M S, Petkowski, Janusz J, Bains, William, Ranjan, Sukrit, Seager, Sara, Clements, David L, Silva, Clara Sousa and Fraser, Helen J 2022. Low levels of sulphur dioxide contamination of Venusian phosphine spectra. Monthly Notices of the Royal Astronomical Society 514 (2) , pp. 2994-3001. 10.1093/mnras/stac1438

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New analysis is presented of the 1.1 mm wavelength absorption lines in Venus’ atmosphere that suggested the presence of phosphine. We retrieve a sulphur dioxide observation from the JCMT archive that was simultaneous within a few days of the PH3 1-0 spectrum obtained in 2017 June, and demonstrate via a radiative transfer calculation that contamination of PH3 by SO2 was ≈10 per cent. We also present ALMA 2019 spectra of PH3 1-0 and an SO2 transition acquired simultaneously, and infer that SO2 line-contamination was ≲2 per cent (for the least-noisy half of the planetary disc). The contamination-subtracted ALMA and JCMT spectra (of 6–8σ sigma confidence) are now consistent with similar absorption-depths at the two epochs. The two values span −1.9(±0.2) 10−4 of the continuum signal (which was re-estimated for ALMA), albeit for differing planetary areas. This suggests that the abundance attributed to phosphine in Venus’ atmosphere was broadly similar in 2017 and 2019.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 27 January 2023
Date of Acceptance: 20 May 2022
Last Modified: 03 May 2023 20:03

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