Is There Life On Venus? Extra-Terrestrial ‘Aerial’ Organisms May Exist In Its Clouds, Say Scientists
by Jamie Carter
There could be microbial life in the clouds of Venus.
Traces of phosphine (PH3)—a gas thought to be a sign of life—has been inferred in the atmosphere of Venus by scientists performing an experiment out of pure curiosity.
It’s possible evidence for the presence of some kind of acid-resistant microbial “aerial” life on another planet. The other explanation is that there is some weird chemistry going on in the cloud tops of Venus that we just don’t understand.
The news—published today in Nature Astronomy—was made by scientists at Cardiff University and the University of Manchester in the UK, and the Massachusetts Institute of Technology (MIT) in the US.
Despite the cautious nature of the news, it’s a big story for anyone interested in the hunt for life beyond Earth. If life arose on two planets in the Solar System then it may be commonplace in the Universe.
“I thought we’d just be able to rule out extreme scenarios, like the clouds being stuffed full of organisms,” said team leader Jane Greaves of Cardiff University in the UK, who first spotted signs of phosphine in observations from the James Clerk Maxwell Telescope (JCMT), operated by the East Asian Observatory, in Hawaiʻi.
“When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”
What is phosphine?
Phosphine, consisting of hydrogen and phosphorus, is a colorless, smelly, flammable, toxic gas on Earth.
Some bacteria on Earth make phosphine, taking up phosphate from minerals or biological material, adding hydrogen, and expelling phosphine.
Phosphine can therefore be described as a potential sign of extraterrestrial life. Where it’s found on Earth—in swamps, penguin dung heaps and the bowels of some badgers and fish—it’s said to smell like rotting fish or garlic.
However, the pure form of phosphine is odorless. In man-made liquified gas form it’s often used as a fumigant.
How did the researchers find phosphine?
A team led by Greaves searched for molecules in the atmosphere of Venus that shouldn’t be there and unexpectedly found a signal of phosphine.
Since these molecules float in the high clouds of Venus (though not around the polar caps), they absorb some of the millimeter waves that are produced at lower altitudes. So by observing Venus in the millimeter wavelength astronomers could see the tell-tale signs of phosphine absorption in their data—essentially as a dip in the light from Venus.
After seeing signs of it in observations from the JCMT at a wavelength of about 1 millimetre, the scientists confirmed their discovery required using 45 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) —currently the largest radio telescope in the world. It’s more sensitive than the JCMT.
How rigorous is the science?
Despite the surprising find, the researchers are confident in their find. “To our great relief, the conditions were good at ALMA for follow-up observations while Venus was at a suitable angle to Earth,” said team member Anita Richards of the UK ALMA Regional Centre and the University of Manchester. “Processing the data was tricky, though, as ALMA isn’t usually looking for very subtle effects in very bright objects like Venus.
“In the end, we found that both observatories had seen the same thing — faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below,” said Greaves.
The researchers emphasize that the detection of phosphine is not robust evidence for life, only for anomalous and unexplained chemistry.
How much phosphine was found in the clouds of Venus?
The researchers found that phosphine exists in Venus’ clouds at a small concentration of twenty molecules in every billion.
These molecules float in the windblown clouds of Venus at altitudes of 35 to 50 miles/55 to 80km.
That may not sound like much, but it’s actually more than could be expected to occur form non-biological sources.
Where could the phosphine come from?
Could the traces of phosphine come from non-biological abiotic (i.e. lifeless) mechanisms on Venus? There’s so much of it in the clouds of Venus that it’s more likely from another source. So the researchers did the math on how much phosphine could be produced by:
- sunlight
- minerals blown upwards from the surface
- volcanoes
- lightning
However, their calculations indicate that these non-biological sources couldn’t make enough phosphine to account for what the telescopes detected. Only one ten thousandth, in fact.
So although phosphine can be produced by abiotic mechanisms, there’s so much of it in the clouds of Venus that it’s more likely to come from another source.
Is there some ‘weird chemistry’ at Venus?
Possibly. “The non-biological production of phosphine on Venus is excluded by our current understanding of phosphine chemistry in rocky planets' atmospheres,” said Leonardo Testi, European Southern Observatory (ESO) astronomer and ALMA European Operations Manager, who did not participate in the new study. “Confirming the existence of life on Venus's atmosphere would be a major breakthrough for astrobiology ... it is essential to follow-up on this exciting result with theoretical and observational studies to exclude the possibility that phosphine on rocky planets may also have a chemical origin different than on Earth.”
Could there really be organisms in the clouds of Venus?
The researchers say organisms on Venus would only need to work at about 10% of their maximum productivity to produce the levels of phosphine the telescopes detected.
That means organisms at Venus—though likely to be very different to anything found on Earth cousins—could be the source of phosphine in its atmosphere.
However, despite the high clouds of Venus having temperatures up to a pleasant 86 ºF/30ºC degrees Celsius, they about 90% sulphuric acid, which would make it difficult for microbes trying to survive there.
In fact, the paper reads: “There are substantial conceptual problems for the idea of life in Venus’ clouds—the environment is extremely dehydrating as well as hyper-acidic.”
If the theory holds about where phosphine must originate from, then we’re talking anaerobic, acid-resistant bacteria.
“The discovery raises many questions, such as how any organisms could survive,” said team member Clara Sousa Silva of the Massachusetts Institute of Technology in the US. “On Earth, some microbes can cope with up to about 5% of acid in their environment — but the clouds of Venus are almost entirely made of acid.”
Why is the detection of phosphine on Venus so exciting?
Earlier this year a paper was published that posited that if NASA’s James Webb Space Telescope detected phosphine in the atmosphere of a rocky planet it would be an unmistakable sign of extraterrestrial life.
In the search for exoplanets that could host life, astronomers look for “biosignature gases”—and phosphine is one of them. Oxygen is also one, of course because of its role on supporting life on Earth. However, the MIT researchers found that phosphine is produced by anaerobic organisms, such as bacteria and microbes, which don’t require oxygen.
So phosphine comes from organisms—albeit extremophiles—which makes phosphine a pure biosignature. It’s also relatively easy to spot in the signature pattern of light from exoplanets, at least from 16 light-years distance.
Is Venus potentially habitable?
Certainly not its surface. It’s hot enough down there to melt metal and its surface often gets coated in sulfuric acid rain. However, the habitability of Venus' clouds has discussed for decades, most recently in a paper published in 2018.
A belt of clouds about 50 km above Venus have long been thought of as a place just as likely as anywhere else in the Solar System to host life. In this lower cloud layer there are favorable-ish conditions for microbial life, including moderate temperatures and pressures.
What happens next?
Confirming the presence of “life” at Venus needs a lot more work, primarily using telescopes, but the researchers say that ultimately it would be helpful to take in-situ measurements or “aerosol return”.
Although the space agency has ignored Venus since its Magellan mission in the 1990s that mapped its surface, NASA now has has two missions on the drawing board:
- VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy): will map Venus' surface to determine the planet's geologic history.
- DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus): will analyze Venus’ atmosphere to understand how it formed and evolved and determine whether Venus ever had an ocean.
Wishing you clear skies and wide eyes.