Indicator of Life on Venus May Just Have Been Sulfur Dioxide

An image of Venus compiled in 1974 using data from the Mariner 10 spacecraft NASA / JPL-Caltech

Last September, the astronomical community was shaken by research that suggested that there might be signs of life on Venus. The researchers found indicators of a gas called phosphine in the Venusian atmosphere, which, to our knowledge, is only produced by anaerobic (non-oxygen-dependent) bacteria.

Since then, scientists have argued back and forth about this finding and whether it was reliable. A new study now suggests that the gas detected was not phosphine but sulfur dioxide, a far more common gas with no special relationship to life.

The new study by researchers at the University of Washington used a computer model of Venus’ atmospheric conditions to understand what might have been giving off the signal that was believed to be phosphine. They think there is a more prosaic explanation for the readings.

“Instead of phosphine in the clouds of Venus, the data agrees with an alternative hypothesis: They detected sulfur dioxide,” co-author Victoria Meadows, a UW professor of astronomy, said in a statement. “Sulfur dioxide is the third most abundant chemical compound in Venus’ atmosphere and is not considered a sign of life.”

The team also says the signal coming from sulfur dioxide is more in tune with what we know about the Venusian environment than phosphine. The surface of Venus is hidden under thick clouds of sulfuric acid, with an atmosphere that is blown by high wind speeds.

The difficulty of finding out whether there is actually phosphine in the atmosphere arises from the methods used to study the planet. Since we cannot directly collect a sample of the Venusian atmosphere, researchers use radio telescopes to view the planet. These radio telescopes show absorption in the radio waves at a certain wavelength – 266.94 gigahertz – which is around the frequency that is absorbed by both phosphine and sulfur dioxide. It is difficult to say which of the chemicals is causing the absorption, which is why there has been debate and a number of studies since attempting to solve this mystery.

This new finding does not definitively refute the hypothesis of phosphine on Venus, but it does make it appear less likely. We will have to wait for more debate and data to come to a definitive answer on our mysterious planetary neighbor and the possibility of life there.

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