The most recent, restless search for new insight began last September, when scientists announced that they had discovered evidence of a gas called phosphine floating in Venus’s clouds. It was quite the surprise: Based on what’s known about phosphine, the gas isn’t supposed to survive for very long in the planet’s atmosphere. On Earth, phosphine has been found in the intestines of animals, us included, and in swampy communities of microorganisms. The group of scientists concluded that something must be replenishing Venus’s supply—perhaps a mysterious Venusian life-form.

Venus instantly became one of the most exciting targets in the search for life beyond Earth. But the phosphine detection was a flicker of evidence, not definitive proof, and the flashy discovery transformed into a slow-burning debate as other scientists joined in. Some researchers said their own analyses turned up empty for phosphine. Others found hints of phosphine buried in decades-old observations. Still others argued that the signal corresponded to an entirely different gas. The original team held on to its conclusions, even after an error in telescope data forced the researchers to revise down the amount of phosphine they had detected. New scientific papers have regularly cropped up since, swinging the discussion in one direction or the other.

The latest entry suggests a rather explosive explanation: If there’s phosphine in Venus’s clouds, it’s probably not because of aliens, but because of volcanoes.