On Monday, astronomers announced that traces of a rare molecule known as phosphine have been found in Venus’s hellish, highly acidic atmosphere, providing a tempting clue that life may exist. The phosphine molecules found on Earth are primarily the result of human activity or microbes that thrive in an oxygen-free environment.

The researchers do not claim that life was discovered on the second planet from the Sun. But observations suggest at least the possibility of microbial activity in the upper atmosphere of Venus, far from the inhospitable surface of the planet.

“We have discovered a rare gas called phosphine in the atmosphere of our neighboring planet Venus,” said Jane Greaves, a professor at Cardiff University in the United Kingdom and lead author of the report published in Nature Astronomy… “And the reason for our excitement is that phosphine gas on Earth is produced by microorganisms that live in an oxygen-free environment. And so there is a chance that we have found some kind of living organism in the clouds of Venus. “

However, the team says much more research is required to confirm any such claim, however extraordinary it may be.

“To make this rather unusual claim that there can be life, we really have to exclude everything, and therefore we are very careful in saying that we are not claiming that there is life, but we are claiming that there is something truly unknown and it could be life, ”said team member William Baines, a researcher at the Massachusetts Institute of Technology.

Sara Seeger, an MIT researcher who studies exoplanet atmospheres, agreed, saying “we are not claiming to have found life on Venus.”

“We are claiming a reliable discovery of a phosphine gas, the existence of which remains a mystery,” she said. “Phosphine can be produced by some (non-biological) processes on Venus, but only in incredibly tiny amounts that are not enough to explain our observations. Thus, we are left with another exciting, tempting opportunity: perhaps there is some kind of life in the clouds of Venus. “

Mars has long been considered the best candidate for a solar system outside of Earth, where microbial life lived in the distant past or even now, as evidenced by background methane levels. NASA, the European Space Agency, China, India, Russia and the United Arab Emirates are all striving exploration of the red planet in one form or another.

NASA is also planning a flagship mission to explore satellites of Jupiter… Scientists believe that this is one of the largest and most famous satellites of the planet, Europeheated by tidal stresses and gravitational interactions with other moons, hides a salty, possibly habitable ocean under its icy crust. Other frozen moons outside the solar system, possibly “water worlds”, are also candidates for study.

But Venus is the victim of a runaway greenhouse effect, in which thick clouds in an atmosphere made up mostly of carbon dioxide trap sunlight, creating surface temperatures that reach nearly 900 degrees, hot enough to melt lead.

However, in the upper layers of the planet’s atmosphere, temperatures are much more favorable. Despite the acidic nature of clouds, scientists have suggested that alien microbes may exist.

“The surface conditions there today are really hostile, the temperature is enough to melt our lander,” Greaves said. “But it is believed that much earlier in the history of Venus, the surface was much cooler and wetter, and life could arise.

“There is a long-standing theory that some of the smallest life forms could have evolved up into high clouds. The conditions there are definitely not pleasant, they are very sour and very windy, but on the other hand, if you are talking about an altitude of 50 to 60 kilometers, then the pressure is very similar to the pressure on the Earth’s surface, and the temperature is pretty good, maybe up to about 85 degrees Fahrenheit. So it was hypothesized that this is a living environment today. “

Greaves’ team studied the spectra of the atmosphere of Venus with the James Clerk Maxwell Telescope in Hawaii and 45 antennas of the Atacama Large Millimeter / Submillimeter Array radio telescope in Chile, and were surprised to find unmistakable indications of phosphine. “It was a shock,” Greaves said.

The discovery was rewarded with additional observation time on the ALMA array, and “we eventually found that both observatories saw the same, weak absorption at the correct wavelength to be phosphine, where the molecules were illuminated from behind by warmer clouds below. Greaves said in a statement.

Only trace amounts were observed, about 20 molecules per billion. But additional research has shown that natural sources of phosphine – volcanoes, lightning, minerals emitted into the atmosphere, exposure to sunlight – only produce one ten-thousandth of the amount actually found.

Scientists can rule out many nonbiological ways of producing observed levels of phosphine, but that doesn’t mean life is the only explanation. Venus’s atmosphere is 90% sulfuric acid, which raises “a lot of questions, like how any organisms can survive,” said MIT researcher Kara Sousa Silva.

“On Earth, some microbes can handle about 5% of the acid in their environment, but Venus’s clouds are almost entirely acid,” she said.

Greaves’ team is awaiting additional time at the telescope to look for signs of other gases associated with biological activity and to determine the temperature of clouds containing phosphine for more information. Ultimately, future visits to spacecraft are likely to be required to fully resolve the issue.

“There can always be something we missed,” Seeger said. “In the end, the only thing that will answer this question for us – whether there is life or not – is actually a flight to Venus and taking more detailed measurements of the signs of life and, possibly, life itself.”