Lack of water rules out life on Venus

A study measuring water concentration in Venus's atmosphere has concluded that life as we know it is not possible among the sulphuric acid droplets that make up the planet's famously cloudy skies.

The search for life on our nearest neighbour has so far proved fruitless, although a 2020 paper rekindled hopes for Venus when it claimed to have detected phosphine gas - known to be produced by bacteria on Earth - in the planet's clouds.

The authors have since called their own findings into question.

But the claim inspired scientists led by Queen's University Belfast to test the theory from a different angle: whether there is enough water in Venus's atmosphere to make life possible.

In 2017, microbiologist John Hallsworth discovered a terrestrial fungus that can survive at 58.5 percent relative humidity - the driest conditions at which biological activity has ever been measured.

"We bent over backwards to argue that the most extreme, tolerant microbes on Earth could potentially have activity on Venus," said Hallsworth at a press conference.

But he said nothing could cope with the miniscule amount of water in the planet's atmosphere, which is equivalent to a relative humidity of 0.4 percent.

"It's more than 100 times too low. It's almost at the bottom of the scale, at an unbridgeable distance from what life requires to be active."

To calculate the concentration of water, scientists used existing measurements from seven US and Soviet probes and one orbiter mission sent to Venus in the late 1970s and early 1980s.

Chris McKay, a NASA planetary scientist and co-author of the research published in Nature Astronomy, noted that the conclusions of the study were based on the limited direct observations available,...