A false-color photo of Venus in ultraviolet light taken by Japan's Akatsuki spacecraft shows textures in the planet's permanently cloudy atmosphere. Unlike clouds on Earth, which are made of water droplets, those on Venus are mostly sulfuric acid. Jaxa-ISAS-DARTS-Damia-Bouic
A false-color photo of Venus in ultraviolet light taken by Japan's Akatsuki spacecraft shows textures in the planet's permanently cloudy atmosphere. Unlike clouds on Earth, which are made of water droplets, those on Venus are mostly sulfuric acid. Jaxa-ISAS-DARTS-Damia-Bouic

Are you kidding? With a surface temperature nearly twice as hot as your highest oven setting, clouds composed of battery acid (sulfuric acid) and a toxic carbon dioxide atmosphere bearing down on the planet with a pressure 90 times that of Earth, Mars looks like the promised land in comparison.

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The Russian Venera landers took these photos of Venus's barren, rocky surface and yellow sky in the early 1980s.Reprocessed by Don Mitchell
The Russian Venera landers took these photos of Venus's barren, rocky surface and yellow sky in the early 1980s.Reprocessed by Don Mitchell

But science is nothing if not full of surprises. An international team of astronomers announced this week the discovery of a rare gas called phosphine in the clouds of Venus. This pyramid-shaped molecule contains three hydrogen atoms bound to a single phosphorus atom and stinks to high heaven. Some describe it as smelling like rotting fish, but I like the more poetic description by this chemistry blogger: "Like rancid gasoline combinedwith rotten watermelons, with undertones of stale sweat,pig carcass,a hint of garlic,moldy oranges, Russian-made aftershaveand a cheaphouseholdair freshener."

On Earth, phosphine gas is made industrially for use in the semi-conductor industry and in fumigants, but microbes that thrive in oxygen-free environments like landfills, swamps and animal intestines produce it naturally. They take up phosphate from minerals or biological material, add hydrogen, and expel phosphine.

Decades ago, astronomer Carl Sagan proposed that the clouds of Venus, where temperatures are more Earth-like ( up to 86 F / 30 C), might be home to similar bacteria that thrive in extremely hot and acidic environments like those found in hot springs at Yellowstone National Park. 30 miles (50 km) up, Venusian clouds would not only provide more clement temperatures but there would also be abundant sunlight, carbon dioxide and possibly water vapor to allow photosynthesis to occur. Or the bacteria could munch on sulfuric acid cloud droplets and material belched into the atmosphere by still-active volcanoes.

"When we got the first hints of phosphine in Venus's spectrum, it was a shock!", says team leader Jane Greaves of Cardiff University in the UK, who first spotted signs of the material in observations from the James Clerk Maxwell Telescope (JCMT) in Hawai?i. The team confirmed the discovery using 45 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Extraterrestrial phosphine isn't new. It was first discovered in the swirly clouds of Jupiter and Saturn several decades ago. The high pressure and heat within their interiors naturally cook up the stinky molecule which rises to the cloud tops where our instruments can detect it. But Venus? While hot and oppressive it doesn't possess anywhere near the crushing heat and pressure found in the gas giant planets. So, what's making this stuff?

The moon hovers above a rapidly growing cumulus cloud that features a cap or pileus of ice crystals. Since 2013, scientists have discovered more than 300 species of bacteria that literally live in Earth's clouds. Bob King
The moon hovers above a rapidly growing cumulus cloud that features a cap or pileus of ice crystals. Since 2013, scientists have discovered more than 300 species of bacteria that literally live in Earth's clouds. Bob King

Although the team only found 20 molecules for every billion that's still 10,000 times the amount that might arise from the non-biological processes they investigated including sunlight,minerals blown upwards from the surface, volcanoes and lightning.To create the observed amount of phosphine on Venus, terrestrial organisms would only need to work at about 10 percent of their maximum productivity, according to the team.

Before we know anything definitive, Greaves and her team will have to confirm their observation by looking for additional signatures of phosphine in other parts of Venus's spectrum, the light reflected by the planet. Though primitive life may explain the current data it's equally if not more likely that another unknown chemical process manufactures the molecule. That would also be a wonderful discovery and add to our knowledge of its origin.

But the best way to find out would be to send a probe to Venus, grab samples from its clouds and return them to Earth, a mission that space-faring nations are fully capable of doing. A couple are under consideration right now.

In science, observation prompts new questions, which lead to further observations, and the road goes ever on.