The discovery of life outside the Earth will probably be one of the most important milestones in human history. Venus, our closest planet, has a suffocating temperature and its surface is an ocean of molten rock and a toxic atmosphere, so it doesn’t seem like the best place to find it.
Yes; there are organisms that survive in the most extreme hot and cold conditions. They have appropriately named Extremophiles, which can thrive in harsh environments. So can we hope to find life in a place like Venus?
An international team of astronomers, led by Professor Jane Greaves of Cardiff University, has just announced, as of 14 September, the discovery of a molecule, phosphine, in the clouds of Venus. On Earth, this gas is only produced industrially or by microbes that thrive in oxygen-free environments. That is, phosphine is considered a biomarker, a sign of life (even if it is microbial).
Does that mean we have found life on Venus? Has the most important milestone in the history of science been achieved? The opinions of the experts indicate, as almost always in terms of scientific findings, that we must be cautious.
We are going step by step to explain this discovery.
What is phosphine?
Phosphine is a molecule consisting of hydrogen and phosphorous, found on Earth and produced by microbes in oxygen-free environments. Terrestrial bacteria absorb phosphate minerals, add hydrogen to the process, and ultimately expel phosphine. This process costs energy, so it is not clear why they do it. Phosphine might just be a waste product, but other scientists have suggested other purposes for it, such as protecting itself from rival bacteria.
How did the discovery come about?
The new discovery is published in a paper published in Nature Astronomy and describes the 2017 detection of this molecule by the James Clerk Maxwell Telescope (JCMT) in Hawaii. This finding was followed up by 45 more telescopes from the Atacama Large Millimeter / submillimeter Array (ALMA) in Chile.
Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes, which would float away from the scorching surface, but would still need to tolerate too high an acidity for them to survive.
Professor Greaves, one of the study’s authors, admits that this was an experiment done out of curiosity: “When we got the first hints of phosphine in the Venus spectrum, it was a shock! ”After six months of data processing, the discovery was confirmed.
The study concluded that phosphine is present in the clouds of Venus, but it is scarce: in only about twenty molecules out of a billion.
Is this a confirmation of life on Venus?
No; this is still a very bold statement. The team believes their discovery is significant because they can rule out many alternative ways of making phosphine, but they acknowledge that confirming the presence of life takes much more work.
Although the high clouds on Venus have temperatures of up to a pleasant 30 degrees Celsius, they are incredibly acidic, around 90% sulfuric acid, posing significant problems for microbes to survive.
In the opinion of David Rothery, professor of planetary geosciences at The Open University: “Today’s announcement of the discovery of phosphine on Venus is not a demonstration that life exists in its clouds. The authors do not claim this, but there is a danger that some media will broadcast the discovery in this way.
What the work does show is that there is phosphine gas in Venus’s atmosphere at a concentration that, while low (around 20 parts per billion), is too high to explain simply.
Rothery has detailed for Science Media Center a possibility of the existence of life on Venus: “Phosphine should not survive long among acid clouds and bathed by ultraviolet rays. However, it could be produced by microbes suspended in the air, in the ‘sweet zone’, at about 50-60 km of altitude. There, the temperature is cold enough for life, at a rate sufficient to match its rate of inorganic decomposition. On the other hand, the surface of the planet, at about 460 ºC, is too hostile for life, and the high The atmosphere is probably the only place where hypothetical organisms could thrive, which could appear in the planet’s now-defunct oceans. If explosive volcanic eruptions continue today, which is starting to seem plausible, this would provide an easy way to deliver nutrients, because microbes cannot even be expected to survive on ‘fresh’ air alone. ”
Could phosphine have a non-organic origin?
The astronomers also performed calculations to see if the phosphine could come from natural processes on Venus. But they warn that some information is missing; in fact, the only other study of phosphorus on Venus came from a landing experiment, carried out by the Soviet Vega 2 mission in 1985.
Dr. William Bains, a scientist at the Massachusetts Institute of Technology, led the work on the evaluation. of inorganic natural ways to produce phosphine. Some ideas included the light of the sun, the minerals were thrown up from the surface, volcanoes or lightning but none of these could produce enough of them: natural sources produce at most one ten-thousandth of the amount of phosphine that the telescopes captured.
What could bacteria from Venus be like?
The discovery raises many questions. Mainly, if there are microbes on Venus, how could organisms survive in such an acidic environment? On Earth, some microbes can cope with about 5% acid in their environment, but the clouds on Venus are made up almost entirely of acid, according to the researchers.
Furthermore, to create the amount of phosphine observed on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity. Mind you, any microbe on Venus is likely to be very different from its terrestrial cousins to survive in hyperacid conditions.
On the other hand, Professor Sara Seager and Dr. Janusz Petkowski, both MIT researchers, are investigating how microbes could protect themselves and live within droplets suspended in the clouds of Venus.
Could there be more life in the solar system?
If the phosphine of Venus is an indicator of life, there may be other potential evidence of organic activity in our solar systems, such as methane from Mars and the escape of liquid water geysers from the icy moons Europa and Enceladus. On Venus, it has been suggested that the dark streaks where ultraviolet light is absorbed could come from colonies of microbes. The Akatsuki spacecraft, launched by the Japanese space agency JAXA, is currently mapping these dark stripes to understand more about this ‘unknown ultraviolet absorber’.
What is the next step?
The team now eagerly awaits more time from the telescope, for example, to establish whether phosphine is in a relatively warm part of the clouds and to search for other gases associated with life. The new space missions could also travel to our neighboring planet and sample clouds in situ to look for more signs of life.