Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations

TL;DR

This study used SOFIA to search for phosphine in Venus's atmosphere, setting a strict upper limit on its abundance and challenging previous ground-based detections.

Contribution

First to use SOFIA for a targeted search of Venusian phosphine, providing more stringent upper limits and refining our understanding of atmospheric composition.

Findings

No detection of phosphine in Venus's atmosphere.

Established a more stringent upper limit of 0.8 ppb for phosphine.

Results challenge previous ground-based detection claims.

Abstract

The presence of phosphine (PH$_3$) in the atmosphere of Venus was reported by Greaves et al. (2021a), based on observations of the J=1-0 transition at 267 GHz using ground-based, millimeter-wave spectroscopy. This unexpected discovery presents a challenge for our understanding of Venus's atmosphere, and has led to a reappraisal of the possible sources and sinks of atmospheric phosphorous-bearing gases. Here we present results from a search for PH$_3$ on Venus using the GREAT instrument aboard the SOFIA aircraft, over three flights conducted in November 2021. Multiple PH$_3$ transitions were targeted at frequencies centered on 533 GHz and 1067 GHz, but no evidence for atmospheric PH$_3$ was detected. Through radiative transfer modeling, we derived a disk-averaged upper limit on the PH$_3$ abundance of 0.8 ppb in the altitude range 75-110 km, which is more stringent than previous ground-based studies.