Venus is common called Earth’s sister planet, a neighboring twin of similar density and size. But the similarity stops there. As the warmest planet in our solar system, the suffocating Venus atmosphere is full of carbon dioxide that coats the heat and clouds dense with sulfuric acid that cover its dry volcanic terrain.
So, this is one of the last places one might think of looking for life outside our planet.
So it came as a shock last September when a group of scientists, led by Jane Greaves of Cardiff University, announced that they had found a possible sign of extraterrestrial life in a Venusian atmosphere. U study, published in Astronomy of nature, reported the discovery of a colorless, poisonous gas called phosphine in the planet ‘s clouds and concluded that no known chemical or geological process could explain its presence. Phosphine could point to life, they argued, noting recent work astrophysicist Clare Sousa-Silva of MIT who suggests that gas could be a signature. On Earth, phosphine is often found in places that host anaerobic life, including lakes, swamps, rice paddies, and sludge in landfills.
But when the news reached Jonathan Lunine, an astronomer at Cornell University, he and graduate student Ngoc Truong were immediately skeptical. “It’s problematic to refer to phosphine as a biosignature on Venus, simply because the environment on Venus is completely different from the environment on Earth,” Truong says. Even on our planet, he says, there is some confusion about whether phosphine is associated with life, and he believes this should be confirmed before we extrapolate these observations to environments as much as ours.
Truong and Lunine were not alone in their suspicions: after the announcement of phosphine, the Internet exploded with discussions about the discovery. Scientists weighed themselves on Twitter threads, argued on Facebook posts and rushed arXiv.org, an overprint server for scientific research, to set up other theories about which nonbiological processes can produce phosphine.
Truong, who had until then studied the oceans on Saturn’s moons, convinced Lunine that they needed to further explore one potential source of phosphine, especially volcanoes. Their research culminated in new study published Monday in the journal Proceedings of the National Academy of Sciences. In it, Truong and Luna paint how phosphine could enter Venus’ atmosphere. Traces of phosphide (negatively charged phosphorus ions bound to metals such as iron) found deep in Venus’s mantle could be extracted to the surface by volcanic activity. When volcanoes erupt, these phosphides can be released into the atmosphere and chemically react with sulfuric acid in the clouds to form phosphine.
“Our research only suggests a roadmap for estimating volcanic eruption levels” on Venus, Truong says. Two conditions are required for this to be a viable explanation. First, the planet must be volcanically active. (Although thousands of volcanoes have been spotted on radar images of Venus, scientists lack data to confirm recent eruptions, because so far, landers can only withstand the raging heat and damping pressure of the venus surface for about an hour.) “And not just active in terms of” Hawaiian-style volcanism, “says Lunine, who usually produces lava flows without much explosiveness. Explosive volcanism is crucial, because there must be a mechanism for releasing phosphide into the atmosphere.
Second, scientists should check to see if phosphine is actually there – and it is is currently a major point of contention. Without this evidence, Lunine says, volcano theory “becomes an empty postulate, not a hypothesis.”