Chemical signature of phosphine, a gas that on Earth is only associated with life, has been spotted in Venusian clouds.
Astronomers have found a potential sign of life high in the atmosphere of neighbouring Venus: Hints there may be bizarre microbes living in the sulfuric acid-laden clouds of the hothouse planet.
Two telescopes in Hawaii and Chile spotted in the thick Venusian clouds the chemical signature of phosphine, a noxious gas that on Earth is only associated with life, according to a study in Monday’s Nature Astronomy journal.
Several outside experts – and the study authors themselves – agreed this is tantalising but said it is far from the first proof of life on another planet.
As astronomers plan for searches for life on planets outside our solar system, a major method is to look for chemical signatures that can only be made by biological processes, called biosignatures.
Three astronomers in Hawaii decided to look at the closest planet to Earth: Venus. They searched for phosphine, which is three hydrogen atoms and a phosphorous atom.
On Earth, there are only two ways phosphine can be formed, study authors said. One is in an industrial process. (The gas was produced for use as chemical warfare agent in World War I).
The other way is as part of some kind of poorly understood function in animals and microbes. Some scientists consider it a waste product, others do not.
Phosphine is found in “ooze at the bottom of ponds, the guts of some creatures like badgers and perhaps most unpleasantly associated with piles of penguin guano”, Clements said.
Study co-author Sara Seager, an MIT planetary scientist, said researchers “exhaustively went through every possibility and ruled all of them out: volcanoes, lightning strikes, small meteorites falling into the atmosphere … Not a single process we looked at could produce phosphine in high enough quantities to explain our team’s findings”.
That leaves life.
The astronomers hypothesise a scenario for how life could exist on the inhospitable planet where temperatures on the surface are about 425 degrees Celsius (800 degrees Fahrenheit) with no water.
“Venus is hell. Venus is kind of Earth’s evil twin,” Clements said. “Clearly something has gone wrong, very wrong, with Venus. It’s the victim of a runaway greenhouse effect.”
But that is on the surface.
Seager said all the action may be 50km (30 miles) above ground in the thick carbon-dioxide layer cloud deck, where it is about room temperature or slightly warmer.
It contains droplets with tiny amounts of water but mostly sulfuric acid that is a billion times more acidic than what is found on Earth.
The phosphine could be coming from some kind of microbes, probably single-cell ones, inside those sulfuric acid droplets, living their entire lives in the 16km-deep (10-mile-deep) clouds, Seager and Clements said.
When the droplets fall, the potential life probably dries out and could then get picked up in another drop and reanimate, they said.
More proof needed
Life is definitely a possibility, but more proof is needed, several outside scientists said.
Cornell University astronomer Lisa Kaltenegger said the idea of this being the signature of biology at work is exciting, but she said we do not know enough about Venus to say life is the only explanation for the phosphine.
“I’m not sceptical, I’m hesitant,” said Justin Filiberto, a planetary geochemist at the Lunar and Planetary Institute in Houston who specialises in Venus and Mars and is not part of the study team.
Filiberto said the levels of phosphine found might be explained away by volcanoes. He said recent studies that were not taken into account in this latest research suggest that Venus may have far more active volcanoes than originally thought.
But Clements said an explanation would make sense only if Venus were at least 200 times as volcanically active as Earth.
NASA has not sent anything to Venus since 1989, though Russia, Europe and Japan have dispatched probes.
The US space agency is considering two possible Venus missions. One of them, called DAVINCI+, would go into the Venutian atmosphere as early as 2026.
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