Astronomers have detected phosphine within the upper atmosphere of Venus and known phenomena can’t explain its origin. This has left researchers with two very exciting possibilities: either there is a completely unknown mechanism that can produce this gas, or the source is biological.
Reported in Nature Astronomy, scientists have seen a spectral signature that is unequivocally phosphine, a gas that on Earth, as far as we know, can only be produced by decaying organic matter or artificially in the lab. They estimated an abundance of 20 parts-per-billion of the gas in Venus’s clouds. The atmosphere of Venus is highly acidic so phosphine should be destroyed unless there was a mechanism to continuously produce it.
The team considered known chemical processes that could be producing the chemical such as volcanos, lightning, or even micrometeorites but models of all of these cannot reproduce what it has been witnessed on Venus.
This fact led to the exciting conclusion that whatever is going on Venus must be something not considered before. It is too early to tell what that is but astronomers are seriously considering every hypothesis. And while proving that the source is biological will be difficult, the team’s work shows that it cannot be discounted.
“We did a lot of calculations of rates at which the molecule could form and be destroyed,” lead author Professor Jane Greaves, from the University of Cardiff, told IFLScience. “For the biotic route, we added an "unknown production source" of the same productivity as organisms on Earth, and tracked the phosphine destruction. We found the hypothetical organisms on Venus would not have to be unrealistically super-productive, for the net amount of phosphine to be what we observed.”
Venus doesn’t look like the most hospitable of worlds; it's not for nothing called Earth's evil twin. Its surface has a temperature of 470°C (880°F), and a pressure equivalent to being 900 meters (2,950 feet) underwater. Temperature and pressure decrease as altitude increases, and between 50-60 kilometers (31-37 miles) above the surface you get in the range of what we experience on Earth.
This important discovery comes from observations by James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array in 2017 and 2019, respectively. Phosphine has been proposed as a good biosignature to spot life on rocky planets beyond the Solar System. The team was using the observation to provide a benchmark for future observations of exoplanets. They did not expect to see phosphine on Venus.
“I was just stunned... I thought we were going to get a null result of modest interest to a few astrobiologists!” Professor Greaves shared with us.
Discussions surrounding life on Venus are set to become very popular but to have certainty on what is producing this phosphine gas, the researchers will need new and deeper studies of the atmosphere of the planet.
“We are trying to do more observations,” Professor Greaves told IFLScience. “Obviously the priority is that people can use telescopes safely, during pandemic conditions. But we hope over the next year or so to get a more detailed map of where the phosphine is – what heights, geographic distribution... and if it changes over time.”
It must be noted, phosphine on Venus is not a detection of alien life but it is an extremely exciting possibility.
“What is obviously intriguing is that phosphine is a potential biosignature of life, as this molecule is a by-product of some microbial metabolism on Earth,” said Dr Brendan Burns, Deputy Director of the Australian Centre for Astrobiology, who was not involved in the study. “As the authors admit themselves the phosphine could simply originate from some unknown geochemical or photochemical reactions. Thus, far more work is needed to follow up these observations, but even a slim possibility of a biosignature of life existing outside Earth has the profound potential to alter our understanding of our very place in the universe."
Over the last few decades, serious efforts have gone into expanding our search for life beyond Earth. Our eyes have been focused on frigid worlds like Mars, ocean moons like Europa and Enceladus, and even methane-rich ones like Titan. Now, it appears extreme worlds like Venus may be in the running too.
“We should explore Venus a bit further, say with new spacecraft,” Professor Greaves concluded. “Also maybe we should keep searching – critically but also maybe optimistically – all these other habitats that could exist!”