Sign of life in the clouds of Venus? Perhaps, but evidence is lacking

Astronomers think they have discovered a gas in the clouds of Venus that may indicate life high up in the planets atmosphere. Their research has appeared in the journal Nature Astronomy.

Evidence for life is certainly not perception, the scientists stress. They speak of abnormal and inexplicable chemistry and say that the gas can be produced by unknown chemical processes or – as on earth – by life.

Venus is a hellish world. At the surface the temperature is about 500 degrees, the air pressure is crushing and the atmosphere consists almost entirely of carbon dioxide. Russian landers who descended into the atmosphere last century lasted for no more than two hours.

High above the surface it is about 30 degrees Celsius, but there are clouds full of caustic sulphuric acid. These make the conditions for potential life difficult; but few terrestrial microbes would tolerate these conditions.

Phosphine

In those sulphuric acid clouds, an international team of astronomers think theyve discovered a rare substance: the molecule of phosphine. On Earth, that molecule is only made by industrial processes and by bacteria that thrive in an oxygen-free environment.

When the astronomers pointed a telescope on the cloud cover of Venus in Hawaii and processed the data, they were totally surprised. It was a shock when we caught the first glimpse of phosphine, says team leader Jane Greaves of British Cardiff University.

To be more sure of observation, 45 large dishes from the ALMA telescope in Chile were aimed at the Venusian cloud cover. This measurement also indicated the presence of phosphine in the high atmosphere of Venus.

The researchers estimate that this is about twenty phosphine molecules per billion molecules. In theory, sunlight, volcanoes or lightning can influence chemical processes that produce phosphine. In addition, the molecule can also arise on the surface.

However, according to the researchers, such non-biological processes cannot produce more phosphine than a ten-thousandth of the estimated amount found. They therefore suspect that the phosphine on Venus is produced by unknown chemical processes or by life.

Scientists disagree about the significance of the research. Astrobiologist Inge Loes ten Kate calls it a very spectacular, but also speculative result. I hope that this will lead to new research into the production of phosphine, so that we can really appreciate this discovery

Not convinced

Sijbren Otto of the University of Groningen tries to create life through chemical processes in his lab. He, too, finds it an intriguing discovery that calls for further research. Yet I am not convinced that there is life on Venus. The fact that there is no direct chemical explanation for the phosphine gas is not such a strong argument in my opinion

It is complicated at all to prove at a distance that there is life on a planet, Otto says. Suppose we were to look at the Earth from space, on the basis of which can you say with certainty that there is life here? You see all kinds of molecules in the atmosphere, but how do you prove that they come from living organisms and not from chemical processes? That is incredibly complicated

Cows and bacteria

Planet researcher Daphne Stam of Delft University of Technology compares the observation with the discovery of methane in the atmosphere of Mars. That gas, too, is a so-called biomarker; a substance that can be produced by living organisms, but also by something else. Cows and bacteria produce methane, but methane is also produced in geological processes

An example of a geological process that is not mentioned in the article in Nature Astronomy is the rustling of iron containing phosphorus. Several scientific publications state that this can release phosphine under acidic conditions. However, according to Stam, there is little iron in Venus atmosphere. There may be more on the surface, but if phosphine is produced there, it is extremely difficult to get into the high atmosphere because of the high atmospheric pressure on the planet

If microbes are already floating in the clouds around our sister planet, they will be hard to find, Stam thinks. We first need to find out where the phosphine is and whether that changes over time. Now all we know is that there is probably phosphine and that it may be a little more around the equator, but we need more details to identify a possible source

Incidentally, the idea that there may be life in the clouds of Venus is not new. That has been suggested for much longer, says Stam. There is also something in the atmosphere that absorbs UV radiation. Organisms can be responsible for that too. And although theres a lot of sulphuric acid in the clouds, bizarre bacteria have also been found on Earth that live under extreme conditions

Meanwhile, Stam is pleased that Venus is back in the spotlight. When it comes to life, the focus is mainly on Mars or Jupiters ice moon Europe. But Venus is also a very interesting planet