Phosphine in Venus' atmosphere: Detection attempts and upper limits above the cloud top assessed from the SOIR/VEx spectra

L. Trompet , S. Robert , A. Mahieux , F. Schmidt (1) , J. Erwin , A. C. Vandaele

1 GEOPS - Géosciences Paris Saclay

Context. Recent detection of phosphine (PH₃) was reported from James Clerk Maxwell Telescope and Atacama Large Millimetre/submillimetre Array observations. The presence of PH₃ on Venus cannot be easily explained in the Venus atmosphere and a biogenic source located at or within the clouds was proposed.
Aims: We aim to verify if the infrared spectral signature of PH₃ is present in the spectra of Solar Occultation at Infrared (SOIR). If it is not present, we then seek to derive the upper limits of PH₃ from SOIR spectra.
Methods: We analyzed the SOIR spectra containing absorption lines of PH₃. We searched for the presence of PH₃ lines. If we did not find any conclusive PH₃ spectral signatures, we computed the upper limits of PH₃.
Results: We report no detection of PH₃. Upper limits could be determined for all of the observations, providing strong constraints on the vertical profile of PH₃ above the clouds.
Conclusions: The SOIR PH₃ upper limits are almost two orders of magnitude below the announced detection of 20 ppb and provide the lowest known upper limits for PH₃ in the atmosphere of Venus.

Keywords: planets and satellites: atmospheres; infrared: planetary systems; techniques: spectroscopic; methods: data analysis

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

L. Trompet, S. Robert, A. Mahieux, F. Schmidt, J. Erwin, et al.. Phosphine in Venus' atmosphere: Detection attempts and upper limits above the cloud top assessed from the SOIR/VEx spectra. Astronomy and Astrophysics - A&A, 2021, 645, ⟨10.1051/0004-6361/202039932⟩. ⟨insu-03745274⟩