Letter to the Editor

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

¹ Planetary Aeronomy, Royal Belgian Institute for Space Aeronomy, Brussels, Belgium
e-mail: loic.trompet@aeronomie.be
² Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium
³ The University of Texas at Austin, Austin, TX, USA
⁴ Université Paris-Saclay, CNRS, GEOPS, 91405 Orsay, France

Received: 17 November 2020
Accepted: 10 December 2020

Abstract

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.