Is phosphine in Venus' atmosphere evidence of finding life?

A planet covered in clouds: images of Venus taken by NASA's Mariner 10 spacecraft.

A team from Cardiff University in the United Kingdom recently discovered phosphine in the clouds of Venus in Hawaii using the James Clay Maxwell Telescope and the Atacama Large Millimeter/Submillimeter Array Telescope in Chile.

This is a very fascinating discovery, because phosphine is a gas produced on Earth only by microorganisms and not by other methods, so it is considered a strong sign of the existence of life activity. This discovery is perhaps the strongest evidence of life beyond Earth to date.

The idea of finding biometrics in other worlds by searching for phosphine was proposed in 2019 by astronomers led by Clara Sousa Silva of the Massachusetts Institute of Technology, a molecule derived from phosphorus that is an important part of RNA and DNA. On Earth, it is produced by anaerobic bacteria, which are microorganisms that do not need oxygen. They absorb phosphate minerals and combine them with hydrogen, releasing phosphine in the process. What's more important on Earth is that phosphine is not produced through any known geological processes.

Susa-Silva's work solves the problem of how astronomers can detect phosphine in the atmospheres of terrestrial planets. The current conclusion is that since there are no other processes on terrestrial planets that produce phosphine, the presence of phosphine will become a definitive biomarker.

But Venus's environment and Earth are completely different. Its surface temperature averages 460 degrees Celsius and has 90 times the air pressure of Earth. Venus' dense atmosphere is made up almost entirely of carbon dioxide, and it is filled with sulfuric acid clouds. Under these extreme conditions, certain unknown chemical reactions may produce phosphine.

However, one problem with the production of phosphine on Venus is the lack of hydrogen. Phosphine is formed from phosphorus atoms bonded to three hydrogen atoms. In the Solar System, Jupiter and Saturn are able to produce phosphine through inorganic processes. This is due to the fact that these planets have large amounts of hydrogen available under high temperatures and high pressure conditions deep inside. So producing phosphine is a relatively simple process, which can then be discharged into its upper atmosphere by convection. But Venus has almost no hydrogen, and it's hard to conceive of an abiotic way to produce phosphine. In addition, even if certain geological reactions occur, coupled with the presence of all possible sources, such as volcanoes and beneficial minerals, it will still be ten thousand times lower than the observed abundance of phosphine.

Although Venus is generally in a hellish state, its upper-end atmosphere is much better, including 47–60 km above the surface of Venus, with temperatures ranging from 0 to 100 degrees Celsius, and atmospheric pressures averaging about Earth's surface air pressure. But Venus's clouds are also dangerous to life: it's unclear how microbes survive at 95 percent sulfuric acid.

So far we need more observations, and there is a great need for other methods to confirm the presence of phosphine. It has been suggested that future missions to Venus could include balloons or winged vehicles to explore this potentially habitable atmospheric area. Meanwhile, NASA is considering two future flights to Venus, one to study planets from orbit, primarily using synthetic aperture radar for observations, and the other to a probe working in Venus's atmosphere. "Radar should be able to provide some clues about the presence of liquid water on the surface, and more critically, the probe may be able to sample cloud composition and look for the presence of phosphine," Limayer said. "If phosphine does prove to be of biological origin, it would mean, surprisingly, that Venus will be the first planet outside of Earth to be found to have life."