Water study may wash out hopes for life on Venus

Hopes of finding life on Venus had already been dashed, but now a new study may have hammered the last nail into the coffin. New modeling of water activity on different solar system planets has found that Venus would be too dry for even the most extreme forms of life – but there may be other contenders in our solar system that we hadn’t considered.

At a glance, Venus sure doesn’t look like a good choice for a home planet. Beneath clouds of sulfuric acid swirling in an atmosphere of 96 percent carbon dioxide, temperatures at the surface soar to 464 °C (867 °F) and the air pressure crushes like you’re 900 m (3,000 ft) beneath the sea.

It sounds like an open-and-shut case, but it’s long been hypothesized that life could find refuge up in the Venusian clouds. At altitudes of around 48 km (30 miles), there’s a layer where temperatures and pressures are much more comfortable, potentially housing clouds of microbes. In fact, mysterious dark patches in these distant skies have had astronomers wondering if we’ve already spotted aliens.

The story received a big boost last September, when a team of scientists reported the detection of phosphine, a gas that can be a biomarker for microbial life, high in the atmosphere of Venus. However, this was refuted by a later study that found that the more likely culprit was sulfur dioxide.

And now, a new study has dealt yet another blow to the idea that Venus could be habitable. Research led by scientists at Queen’s University Belfast have found that the planet’s atmosphere wouldn’t have anywhere near enough water for any kind of life as we know it to survive.

The team started by analyzing data from probes that have visited Venus in the past, examining the water vapor abundance and temperature of the atmosphere. From that, they were able to calculate how much water would be available for any potential life to take advantage of.

“The search for extraterrestrial life has sometimes been a bit simplistic in its attitude to water,” says Philip Ball, co-author of the study. “As our work shows, it’s not enough to say that liquid water equates with habitability. We’ve got to think too about how Earth-like organisms actually use it – which shows us that we then have to ask how much of the water is actually available for those biological uses.”

The team calculated that water activity as a value that could be compared to that required by the hardiest forms of life on Earth. If water activity of 0.585 is the limit for known life, Venusian clouds are two orders of magnitude drier, with a water activity value of just 0.004.

That seems to put a damper on life on Venus, but this approach may have intriguing implications for other planets in our solar system – and beyond. The team calculated that the atmosphere of Mars comes in just under the apparent habitable range, with a water activity value of 0.537.

Jupiter, meanwhile, just squeezes over the line. The team says that some regions may even have the right temperature, but other factors, like the composition of the gas itself, may limit any potential habitability.

“While our research doesn’t claim that alien (microbial-type) life does exist on other planets in our solar system, it shows that if the water activity and other conditions are right, then such life could exist in places where we haven’t previously been looking,” says John Hallsworth, lead author of the study.

We may not have to wait too long to find more definitive answers. NASA, ESA and private firm Rocket Labs have all announced plans to send probes to Venus in the next decade or so, which should help us better understand our turbulent neighbor – and check if anybody’s home.

The research was published in the journal Nature Astronomy.

Source: Queen’s University Belfast

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