Low Levels of Sulphur Dioxide Contamination of Phosphine Spectra from Venus' Atmosphere

Left panel, (a): ALMA wideband spectrum of SO2 133,11-132,12 (red histogram) for half the planetary disc, as described in the text. The black curve is an upper-limit model, for 15 ppb of SO2 at all altitudes ≥80 km, and without any baseline-fitting. Right panel, (b): spectrum at the PH3 1-0 frequency (blue histogram) for the same planetary area. The black curve is the corresponding 15 ppb upper-limit model for the SO2 309,21–318,24 transition.

New analysis is presented of the 1.1 mm wavelength absorption lines in Venus' atmosphere that suggested the presence of phosphine.

We confirm that ALMA detected absorption at the PH3 1-0 wavelength in 2019, from an optimised spectrum covering half of the planetary disc. Sulphur dioxide line-contamination was then <10%, from modelling of a simultaneous ALMA spectrum of SO2. We retrieve an SO2 observation from the JCMT archive that was simultaneous within a few days of the PH3 1-0 spectrum obtained in June 2017, and demonstrate that contamination was also <10%.

The contamination-subtracted ALMA and JCMT spectra (of 6-7 sigma confidence) are now consistent with similar levels of absorption. The variation is ~25% around -1.5 10-4 of the continuum, albeit not for identical planetary areas. This similarity suggests the abundance that can be attributed to phosphine in Venus' atmosphere was broadly similar in 2017 and 2019.

Jane S. Greaves, Paul B. Rimmer, Anita M. S. Richards, Janusz J. Petkowski, William Bains, Sukrit Ranjan, Sara Seager, David L. Clements, Clara Sousa Silva, Helen J. Fraser

Comments: Submitted to The Astrophysical Journal Letters on 8/18/2021
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2108.08393 [astro-ph.EP] (or arXiv:2108.08393v1 [astro-ph.EP] for this version)
Submission history
From: Janusz Petkowski
[v1] Wed, 18 Aug 2021 21:15:12 UTC (299 KB)
Astorbiology, Astrochemistry,

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