Does phosphine on Venus indicate life?

There is ongoing scholarly debate about whether phosphine exists on Venus. If it does exist, then this may be an indicator of biological processes. Obviously, it is of significant interest to humanity to learn whether life has emerged on other planets. To learn more about the potential presence of phosphine on Venus and its implications, we spoke to Priya Hasan. She is a professor in the Department of Physics at Maulana Azad National Urdu University in India.

What is currently known about phosphine’s presence on Venus?

Per the scientific method, independent analysis of the data used in a scientific paper should lead to similar results. Two teams at the University of Washington in Seattle and at the University of Leiden in the Netherlands analyzed data published in the original paper claiming phosphene existed on Venus. The papers concluded that what the original team thought was phosphine is actually sulfur dioxide (SO2). The two papers’ results have been refuted by the original paper’s authors. Hence, as of now, the presence of phosphine on Venus is debatable. There is a possibility phosphene exists on Venus, but it is not confirmed. The answer to the question is thus “I’m not sure.” To definitively say whether phosphene exists on Venus requires further observations from ground-based telescopes or planned missions to the planet. Data analysis and techniques must include a wide range of caveats and debatable methodologies. The spirit of science lies in the questioning and verification of results.

Why might the presence of phosphine indicate that Venus hosts life?

Phosphine is similar to ammonia, made of a single atom of phosphorous and three atoms of hydrogen. On Earth, we have a phosphine abundance of one part per trillion. In an oxidizing environment, phosphine will immediately react with oxygen to form phosphorous acid or phosphoric acid. On Venus, the original paper’s authors found a phosphine abundance of 20 parts per billion. That’s 1,000 times more prevalent than on Earth.

Phosphine is exclusively associated with life; on our planet, it is not generated by other natural processes involving geology or the atmosphere. Phosphine’s presence in an oxidizing atmosphere indicates constant generation caused by biological processes exceeding the rate of oxidation. That’s why it’s considered a reliable biomarker. If we can prove that phosphine on Venus, if it exists, is produced through biotic instead of abiotic pathways, this would imply significant biomass in the Venusian atmosphere.

What future research areas could more definitively determine the implications of phosphine’s presence on Venus?

Fresh observations are being planned at frequencies different from those in the original paper to confirm the detection of phosphine. For example, observations using the NASA Infrared Telescope Facility (NASA IRTF), a three-meter telescope in Hawaii, are being planned. This work requires original observation techniques as most telescopes are designed to look at faint sources. In this case, Venus is very bright and hence methods need to be planned to adapt to this brightness to avoid saturation of the detectors. The James Webb Space Telescope can look for such signals on faraway planets, but in this case, Venus is too bright for its detectors.

There are also new missions for making in-situ measurements of the Venusian atmosphere to help build more realistic models. The orbiter and atmospheric balloon mission Shukrayaan-1 by the Indian Space Research Organisation is under development and planned for 2023. The orbiter and lander Venera-D by Roscosmos is under development and planned for 2026. NASA has proposed a secondary payload VAMP for the Venera-D lander. Recently, NASA announced it has selected two more missions – DAVINCI+ and VERITAS – to visit Venus in the 2028-2030 timeframe.