While most eyes are on Mars as the most likely place we might find life beyond Earth, perhaps we should be looking to our neighbor on the other side. High in the atmosphere of Venus, astronomers have made the startling discovery of a gas called phosphine – a strong contender for a sign of microbial life.
Phosphine is a molecule that’s relatively rare here on Earth, and when it does show up in nature it’s usually expelled by bacteria and other microbes that don’t breathe oxygen. Since it can’t be produced in any meaningful quantity by other known processes, last year MIT researchers suggested that phosphine could be a useful biosignature for life on other planets. And now it seems the hunt has already borne fruit, very close to home. A team of astronomers – including some of the same researchers from that previous study – have now found phosphine in the atmosphere of Venus.
With surface temperatures of up to 464 °C (867 °F) and atmospheric pressure that’s almost 100 times higher than the Earth’s, Venus is far from a paradise. But it’s long been hypothesized that microscopic life could find refuge high in the atmosphere, at altitudes between around 53 and 62 km (33 and 38.5 mi) where temperatures are much cooler. This new detection of phosphine adds weight to the hypothesis – but on the downside, the clouds up there are made of sulfuric acid, which could be a challenge for any kind of life as we know it.
“Finding phosphine on Venus was an unexpected bonus!” says Clara Sousa Silva, a researcher on the study. “The discovery raises many questions, such as how any organisms could survive. On Earth, some microbes can cope with up to about 5 percent of acid in their environment – but the clouds of Venus are almost entirely made of acid.”
Using the James Clerk Maxwell Telescope (JCMT) and the Atacama Large Millimeter/submillimeter Array (ALMA), the team spotted the spectral signature of phosphine, and estimated its concentration to be about 20 parts per billion.
Intriguingly, the team says that the sulfuric acid in those clouds should be constantly eating away at the phosphine, which means that some mechanism is regularly replenishing supplies. But could that be life?
The researchers explored a range of potential natural processes that could be producing phosphine, including sunlight, lightning, volcanic activity, or minerals drifting up from the surface. But by their calculations, none of these could account for the amount of the gas that was detected – there was 10,000 times more phosphine than would be expected from these processes.
On the other hand, the team estimated that organisms could produce this volume of phosphine while working at just 10 percent of their expected productivity.
As exciting as the discovery may be, it’s far from confirmation of aliens.
“This is huge: it could be the first detection of life beyond Earth,” says Danny Price, an Australian Project Scientist for Breakthrough Listen who wasn’t involved in the study. “If life can arise in hyperacidic clouds on Venus, it may be that life is widespread across the galaxy. But before we get too excited, we need to take a deep breath of that Venusian air and rule out less exciting ways that phosphine could be sneaking in.
“There could be some complex mechanisms replenishing phosphine in the atmosphere of Venus, that we haven’t seen happen here on Earth. We need to do intense follow-up observations to provide further evidence.”
And no doubt these kinds of investigations will follow. Hopefully we’ll have an answer to the age-old question soon.
The research was published in the journal Nature Astronomy.