Phosphine gas found in Venus's atmosphere may be ‘a possible sign of life.’ Venus clouds appear to contain a smelly, toxic gas that could be produced by bacteria, a new study suggests. Phosphine is a chemical compound made up of one atom of phosphorus and three atoms of hydrogen, and scientists have also spotted it on Earth, Jupiter and Saturn. The discovery that the atmosphere of Venus absorbs a precise frequency of microwave radiation has just turned planetary science on its head. An international team of scientists used radio telescopes in Hawaii and Chile to find signs that the clouds on Earth’s neighboring planet contain tiny quantities of a molecule called phosphine. On Earth, phosphine is only produced by microbial life (and by various industrial processes) – and the concentration in our atmosphere is in the parts per trillion range. The much higher concentration on Venus cannot be ignored. To determine whether the phosphine on Venus is really produced by life, chemists and geologists will be trying to identify other reactions and processes. Meanwhile, biologists will be trying to better understand the microbes that live in Venus-like conditions on Earth – high temperatures, high acidity, and high levels of carbon dioxide – and also ones that produce phosphine. When Earth microbes produce phosphine, they do it via an “anaerobic” process, which means it happens where no oxygen is present. It has been observed in places such as activated sludge and sewage treatment plants, but the exact collection of microbes and processes is not well understood. Biologists will also be trying to work out whether the microbes on Earth that produce phosphine could conceivably do it under the harsh Venusian conditions. If there is some biological process producing phosphine on Venus, it may be a form of “life” very different from what we know on Earth.