Venus' atmosphere holds so little water that even Earth's most drought-resistant microbes couldn't survive, a new study reveals. Yet, Jupiter offers a faint glimmer of possibility.
Last year, astronomers detected phosphine in Venus' atmosphere—a gas sometimes linked to life—sparking excitement. While the planet's scorching surface rules out biology, its clouds at 35-50 km altitude mimic Earth's pressure and temperatures, keeping the idea alive. However, recent research identified that phosphine signal as likely sulfur dioxide. Now, a peer-reviewed paper in Nature delivers a definitive blow: Venusian clouds lack the water needed for any known life forms.
Microbiologist John Hallsworth and colleagues at Queen's University Belfast analyzed probe data on temperature, humidity, and pressure within Venus' sulfuric acid clouds. They calculated "water activity"—a key metric for life's viability, scored from 0 to 1. Earth's extremophiles survive down to 0.585, but Venus clouds register just 0.004.
"The water concentration in these clouds is over 100 times too low for even Earth's toughest organisms to endure," Hallsworth states. "It's an insurmountable barrier."
Co-author Chris McKay, an astronomer, emphasizes the data's solidity: "This comes straight from measurements, not models. Upcoming NASA and ESA missions will confirm the same temperatures and pressures—Venus hasn't changed in that timeframe."
The team extended their analysis to other worlds. Mars' clouds hit 0.537 water activity—below viable levels—plus freezing temperatures, high UV radiation, and inhospitable conditions for microbes.
Jupiter's clouds, however, at temperatures from -40°C to 10°C, reach the critical 0.585 threshold. "Unexpectedly, Jupiter offers the right temperature and water activity for active life," Hallsworth notes. "Nutrients remain uncertain, but water checks out."
