Intriguing ‘life’ signal on Venus was ancient sulfur dioxide, new research finds

Scientists stunned the world last timeear pretending to have discovered traces of phosphine in the Venusian clouds. New research suggests this gas – which,, is produced by microbes– was not really responsible for the detected signal. Instead, it was probably sulfur dioxide, a not-so-exciting chemical.

Extraordinary research published in Nature last September is challenged by an article due for publication in The Astrophysical Journal, a pre-print of which is currently available to arXiv. This is not the first article to criticism the apparent discovery of phosphine on Venus, and it probably won’t be the last.

The fact that phosphine was present on Venus was a revelation that blew us away, and that’s because living organisms are one of the only known sources of the stinky gas. The team responsible for the apparent discovery, led by Cardiff University astronomer Jane Greaves, found evidence in spectral signals collected by two radio antennas: the James Clerk Maxwell Telescope (JCMT) and the Large Millimeter Array / Atacama submillimeter (ALMA). Spectral lines at certain wavelengths indicate the presence of specific chemicals, and in this case implied the presence of phosphine in the Venusian cloud layer.

The authors of the Nature study did not claim that life exists on Venus. Rather, they asked the scientific community to explain their rather bizarre sighting. In fact, it was an exceptional claim, as it implied that Venus – one of the most inhospitable planets in the solar system – might in fact be habitable, with microscopic organisms floating through the clouds.

Alas, this does not appear to be the case.

“Instead of phosphine in the clouds of Venus, the data is consistent with an alternative hypothesis: they detected sulfur dioxide,” said Victoria Meadows, co-author of the new study and professor of astronomy at the ‘University of Washington, in a declaration. “Sulfur dioxide is the third most common chemical compound in the atmosphere of Venus, and it is not considered a sign of life.”

Meadows, along with researchers from NASA, the Georgia Institute of Technology, and the University of California at Riverside, came to this conclusion by modeling the conditions inside the Venusian atmosphere, which they did to reinterpret the radio data collected by the original team.

“It’s called a radiative transfer model, and it incorporates data from decades of Venus observations from several sources, including observatories here on Earth and space missions like Venus Express,” he said. explained Andrew Lincowski, researcher at UW. Department of Astronomy and the main author of the article, in the statement.

Equipped with the model, the researchers simulated spectral lines produced by phosphine and sulfur at several atmospheric altitudes on Venus, as well as how these signatures were received by ALMA and JCMT. The results showed that the shape of the signal, detected at 266.94 gigahertz, likely originated from the Venusian mesosphere – an extreme height where sulfur dioxide can exist but phosphine cannot due to the harsh conditions there, according to the report. researches. In fact, this environment is so extreme that the phosphine would not last more than a few seconds.

As the authors argue, the original researchers underestimated the amount of sulfur dioxide in the Venusian atmosphere and instead attributed the 266.94 gigahertz signal to phosphine (phosphine and sulfur dioxide absorb radio waves around this frequency). This happened, the researchers said, due to an “unwanted side effect” known as spectral line dilution, explained Alex Akins, study co-author and NASA JPL scientist. .

“They deduced a weak detection of sulfur dioxide due to [an] ALMA’s artificially weak signal, ”added Lincowski. “But our modeling suggests that the diluted online ALMA data would always have been consistent with typical or even significant amounts of sulfur dioxide from Venus, which could fully explain the observed JCMT signal.”

This new result could prove devastating for the Nature article, and it will be interesting to hear how the authors respond to this latest criticism. That said, some scientists believe the writing is already on the wall, or more accurately, the trash.

“Already soon after the publication of the original work, we and others put strong doubts on their analysis,” wrote Ignas Snellen, professor at Leiden University, in an email. “Now I personally think this is the final nail in the coffin of the phosphine hypothesis. Of course, one can never prove that Venus is completely phosphine-free, but at least there is now no evidence remaining to suggest otherwise. I’m sure others will keep looking.

In December, Snellen and his colleagues took issue with the Nature study, arguing that the method used by Greaves’ team resulted in a high signal-to-noise ratio “false” and that there was “no statistical evidence” for it. phosphine on Venus.

The apparent absence of phosphine on Venus, and therefore the absence of any trace of microbial life, is much less interesting than the other way around, but that’s how it sometimes happens. Science does not claim or promise the best interests of all things, and we, as defenders of the scientific method, must come to accept our developing universe as we find it.