Recovering Phosphine in Venus' Atmosphere from SOFIA Observations

TL;DR

This study reanalyzed SOFIA spectral data to detect phosphine in Venus' atmosphere, revealing a potential higher abundance than previous reports and suggesting active processes or sources that merit further investigation.

Contribution

It demonstrates that correcting calibration artefacts in SOFIA data can lead to a candidate detection of phosphine at about 3 ppb, challenging prior lower estimates.

Findings

Candidate phosphine detection at ~3 ppb above clouds

Phosphine abundance shows an inverted trend with altitude

Sunlight exposure influences observed phosphine levels

Abstract

Searches for phosphine in Venus' atmosphere have sparked a debate. Cordiner et al. 2022 analyse spectra from the Stratospheric Observatory For Infrared Astronomy (SOFIA) and infer <0.8 ppb of PH3. We noticed that some spectral artefacts arose from non-essential calibration-load signals. By-passing these signals allows simpler post-processing and a 5.7{\sigma} candidate detection, suggesting approx. 3 ppb of PH3 above the clouds. Compiling six phosphine results hints at an inverted abundance trend: decreasing above the clouds but rising again in the mesosphere from some unexplained source. However, no such extra source is needed if phosphine is undergoing destruction by sunlight (photolysis), to a similar degree as on Earth. Low phosphine values/limits are found where the viewed part of the super-rotating Venusian atmosphere had passed through sunlight, while high values are from views moving into sunlight. We suggest Venusian phosphine is indeed present, and so merits further work on models of its origins.