False joy: the signs of a possible extraterrestrial life, it will not be this time.
Since they claimed, with great noise, last September, to have found a trail around Venus, astronomer Jane S. Greaves and her colleagues have been deceived several times.
Today, researchers at the University of Washington are retracing the events that would have led to what they consider to be a mistake.
Their thesis: what we would have found in the clouds of Venus would not be phosphine, the compound on which the supposed discovery is based, but vulgar sulfur dioxide.
On Earth,
phosphine
is a molecule known to be produced by anaerobic microbes, that is, living in environments without oxygen.
Detecting the presence of this supposed biological marker in the clouds of Venus would be encouraging but would not be enough to claim that life is there.
Living things as they are conceived also need water.
However, the latter rapidly evaporates in the atmosphere of the planet.
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?
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The
sulfur dioxide
, for its part, is "not considered a sign of life," says Victoria Meadows in an article published Wednesday on the website of the University of Washington.
It is the third most common chemical compound in the atmosphere of Venus, but in negligible amounts when compared to carbon dioxide.
How can we confuse two molecules?
You should know that to identify the composition of a star, we study the waves it emits and more precisely the wavelength spectra.
This is because chemical compounds absorb waves at lengths that are distinct from each other.
A line (or a combination of lines) on the spectrum is the signature of an element, signaling its presence.
In 2017, Jane S. Greaves' team, using the James Clerk Maxwell Telescope (JCMT) in Hawaii, discovered a line at a frequency close to waves absorbed by phosphine and sulfur dioxide.
To decide between the two, in 2019 she used another telescope, ALMA, in Chile.
From the analysis of the frequencies corresponding to sulfur dioxide, she concluded that this compound was present in too small an amount in the Venusian atmosphere.
It could only be phosphine.
Problem: Even the best instruments in the world have flaws.
At the time of the 2019 sighting, ALMA was configured in such a way that it underestimated the levels of sulfur dioxide in the Venusian atmosphere, confusing researchers, as revealed by the new study to appear in Astrophysical Newspaper.
Lack of luck or of caution?
Would the work directed by Jane S. Greaves have paid for the vagaries of a telescope?
“Each instrument has its own strengths and weaknesses.
It is the art of the experimenter to ensure that he is not overinterpreting a signal, ”explains Francis Rocard, head of the Solar System exploration program at the National Center for Space Studies. (Cnes).
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In the case of the pseudo-discovery of phosphine, another element could have put the chip in the ears of scientists: the disputed line between this gas and sulfur dioxide shows an absorption not in the clouds of Venus, but 80 km above, in a part of the atmosphere called the mesosphere.
At this altitude, "harsh chemicals and ultraviolet radiation would shred phosphine molecules in seconds," according to the authors of the new article, who did not respond to our requests for clarification.
“One of the arguments that has been put forward by those who are skeptical about this detection is that there is only one line that has been detected.
To prove the existence of a molecule, it's a bit weak.
We prefer to have at least two, ”continues Francis Rocard.
After the publication of the controversial study, French astrophysicist Thérèse Encrenaz set out to search for a second line that could correspond to phosphine in data from the Maunakea Observatory in Hawaii.
She never found one.
For Francis Rocard, a scientist should not forget the precept stated by the famous American astronomer Carl Sagan: “
Extraordinary discoveries require extraordinary proof
.
It takes solid arguments to say things that are exceptional.
For an extraordinary discovery to be confirmed, two independent teams, with different instruments, would have to find the same measurements.
After the first criticisms of her work, Jane S. Greaves' team had written several articles while partially maintaining their results.
Contacted about the latest arguments contradicting her theory, the Cardiff University researcher cracked an email as sympathetic as it was concise: “We are in discussion with the authors to better understand their methods.
Thank you !
"