The cloud layer of the planet Venus seen by the Japanese probe Akatsuki.

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JAXA

It is a discovery which is debated in the scientific community.

Researchers have established the "apparent presence" of phosphine, a gas existing on Earth, in the cloud layers of Venus, and wonder about its origin, according to a study published Monday in

Nature astronomy

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If a biological origin is possible - and for some holds the rope - it is too early to rule out an unknown phenomenon of photochemistry or geochemistry due to conditions of extreme pressure and temperature.

This is the first time that this compound has been discovered in one of the four terrestrial planets of our solar system, "the Earth apart," Jane S. Greaves, professor of astronomy at AFP, told AFP. Cardiff University, which led the study.

The phosphine was detected by observing the Venusian atmosphere using two radio telescopes - which theoretically rules out an instrument error.

It "could come from unknown processes of photochemistry or geochemistry, or, by analogy with the biological production of phosphine on Earth, thanks to the presence of life", explains the study.

This compound is found in the gas giant planets of the solar system, but it is not of biological origin.

Microorganisms in temperate clouds?

The presence of phosphine, a highly toxic compound, does not mismatch in the hellish atmosphere of the second planet closest to the sun.

Also known as the Shepherd's Star, its atmosphere of carbon dioxide, at 97%, bathes in a surface temperature of around 470 ° C with a pressure more than 90 times greater than ours.

But it is in the thick layer of hyper acidic clouds, covering the planet up to around 60 km of altitude, that the team of Prof. Greaves supposes that the molecules of phosphine can be found.

"There the clouds are 'tempered around 30 degrees Celsius", according to the study, which does not exclude that the gas forms at a lower and warmer altitude before rising.

But where does it come from?

Prof. Greaves "hopes to have taken into account all the processes likely to explain its presence in the atmosphere of Venus".

Unless you identify a new one, there remains the hypothesis of a form of life.

In this hypothesis, "we think that it should be small, to float freely," explains the scientist, whose study "insists that the detection of phosphine is not robust proof of life, only abnormal and unexplained chemistry ”.

This study notes that "the photochemistry of droplets from Venusian clouds (of sulfuric acid) is completely unknown".

This is why Pr. Greaves and his colleagues argue for a more in-depth observation of the phenomenon, first to confirm it.

Ideally free of the "filter" of the Earth's atmosphere, thanks to a space telescope.

And why not with a new visit, by probe, of Venus or its atmosphere.

Previous false alarms

"Between an unknown chemistry, an unknown geology and an unknown biology, biology will always be the last hypothesis far behind the other two", tempers on Twitter the NASA astronomer Jessie Christiansen.

According to her, even if "the telluric planets are different from the gas giants, we are very far from having ruled out chemistry and geology as possible sources" of this phosphine.

Okay, here's what I told folks who asked about the detection of phosphine (PH3) in the atmosphere of Venus: If you give me the options of unknown chemistry, unknown geology, or unknown biology, then biology is always going to be a distant third behind the other two options.

- 🪐🛰 Dr. Jessie Christiansen 🪐 (@aussiastronomer) September 14, 2020

Sarah Hörst, planetologist from Johns Hopkins University, recalls that in the 1980s, the detection of carbon monoxide on Titan had stirred up the scientific community.

But it wasn't until 2008 that geysers on neighboring Enceladus were discovered to be ejecting water into Saturn's atmosphere which then interacted with Titan's chemistry.

Come on, future missions to Venus could provide a better understanding of this mysterious phenomenon.

  • Astronomy

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