Astronomers have found apparent signs of phosphine gas in the cloud decks of Venus, a chemical marker that may be associated with the presence of life on Earth’s closest planetary neighbour.

In a paper published in the journal Nature Astronomy on September 14, 2020, researchers — who include Canadian Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology — state signs of phosphine gas have been detected in in Venus’s atmosphere, “where any phosphorus should be in oxidized forms.”

The new paper also references a January article in the journal Astrobiology that proposed “any phosphine detected in a rocky planet’s atmosphere is a promising sign of life.”

“Trace PH₃ in Earth’s atmosphere (parts per trillion abundance globally) is uniquely associated with anthropogenic activity or microbial presence — life produces this highly reducing gas even in an overall oxidizing environment,” the paper states. “PH₃ is found elsewhere in the Solar System only in the reducing atmospheres of giant planets, where it is produced in deep atmospheric layers at high temperatures and pressures, and dredged upwards by convection.”

But don’t prepare your messages to Venusians just yet. The September paper also notes the presence of phosphine gas is not “robust evidence for life,” adding that there are substantial conceptual problems for the idea of life in Venus’s clouds, as their environment is “extremely dehydrating and hyperacidic.” The writers suggest the answer could come from a mission to Venus for in situ measurements or an aerosol return.

“If no known chemical process can explain PH₃ within the upper atmosphere of Venus, then it must be produced by a process not previously considered plausible for Venusian conditions,” the paper states. “This could be unknown photochemistry or geochemistry, or possibly life. Information is lacking — as an example, the photochemistry of Venusian cloud droplets is almost completely unknown.”