Venus. A particular gas, phosphine, which on Earth is linked to anaerobic life forms, has been detected in the clouds that make up Venus’ atmosphere. Jane Greaves and colleagues, as stated in our press release accompanying the research, observed Venus with the James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array in 2017 and 2019, respectively. They detected a unique spectral signature of phosphine and estimated an abundance of 20 parts per billion of phosphine in Venus’ clouds at an altitude of 53 km, at a temperature of 30°C and a pressure of 1 bar. Conditions on Venus’ surface are hostile to life, but the environment where it has been observed is the upper part of the clouds—about 53–62 km above the surface—where conditions would be more temperate. However, the composition of the clouds is highly acidic, and in such conditions, phosphine would be destroyed very quickly. Then, in early 2021, it was shown that the data were consistent with an alternative hypothesis to phosphine in Venus’s clouds: the researchers were likely detecting sulfur dioxide, explains a study by the University of Washington, NASA’s Jet Propulsion Laboratory, Goddard Space Flight Center, the Georgia Institute of Technology, NASA Ames Research Center, and the University of California, Riverside. In their study, the scientists show that sulfur dioxide—at levels plausible for Venus—not only can explain the observations but is also more consistent with what astronomers know about the planet’s atmosphere and its harsh chemical environment, which includes clouds of sulfuric acid. Furthermore, the signal on which the 2020 work was based would not have originated in the planet’s cloud layer but far above it, in an upper layer of Venus’s atmosphere where phosphine molecules would have been destroyed within seconds. This further evidence also supports the hypothesis that sulfur dioxide produced the signal.
