Phosphine in Venus’ Atmosphere Could Indicate Life in the Clouds

The clouds of Venus where phosphine, a possible biosignature, was detected by Jane Greaves (Cardiff University) and colleagues using Earth-based telescopes. Credit: JAXA/ISAS/Akatsuki Project Team.

The present-day conditions on the surface of Venus are notably extreme with pressures of up to 100 bar — equivalent to being more than 900 meters (3000 feet) underwater on Earth — and temperatures rising up to 900°F (480°C). These conditions will eventually crush spacecraft and melt metal, so it is hard to imagine them supporting life. At altitudes of 60 kilometers and higher above the surface of Venus, though, the environment is more temperate. The pressure is a more relatable 0.5 bar with temperatures of around 85°F (30°C); however, these clouds are highly acidic and the atmosphere is severely dehydrating, hindering the survivability of life as we know it. Yet, a study led by Jane Greaves at the University of Cardiff has detected phosphine (PH3), an organic compound consisting of three hydrogen atoms bonded to a phosphorous atom, in Venus’ atmosphere. On Earth, phosphine is highly reducing and only associated with life that does not need oxygen to survive (anaerobic microbes), particularly when it is produced in an oxidizing environment that would otherwise break down the compound. Barring an uncharacterized abiotic mechanism operating under conditions similar to Venus’ atmosphere, phosphine is thought to only form in significant concentrations as a result of biological activity, making it a compelling potential biosignature.

The team used the James Clerk Maxwell Telescope to analyze the sunlight reflected by Venus for any characteristic dips in the spectrum that could relate to absorption by biosignature gases in its atmosphere. Follow-up observations using the Atacama Large Millimeter/submillimeter Array confirmed the detection of phosphine at a modeled abundance of approximately 20 parts per billion. The team argues that thermodynamic modeling of relevant chemical reactions over a wide range of pressures and temperatures encompassing the conditions found in Venus’ atmosphere, surface, and subsurface cannot produce phosphine in the volume observed. This suggests that either life or an unknown photochemical or geochemical process is producing the observed phosphine. In order to fully distinguish whether or not life is responsible for the atmospheric phosphine, future exploration and study of Venus’ clouds and surface will be required. Perhaps the next spacecraft to the second planet will be equipped to search for the source of the phosphine. READ MORE