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The atmosphere of Venus contains traces of a molecule that only microbial and human activities generate on our planet., and that it smells rotten in association with other compounds. The discovery, made with the James Clerk Maxwell and ALMA telescopes, points to the existence of unknown geological or chemical processes on our neighboring planet, although a possible biological source is not ruled out either.
The phosphine or phosphane o Phosphorous trihydride (PH3) is a colorless, flammable, toxic and odorless gas in its pure state, although it often smells like garlic or rotten fish when it is presented together with other similar compounds. This substance is found in environments such as bogs or feces.
On Earth, only some anaerobic microorganisms produce phosphine, in addition to that which is generated artificially in industrial processes. It is used, for example, in the manufacture of semiconductors to introduce phosphorus into silicon crystals.
But this week an international team of researchers led by ProfessorJane Greaves from Cardiff University (UK) reports in the magazineNature Astronomy who have detected phosphine in an unexpected place: theatmosphere of venus.
The finding has aroused expectations as to whether some form of life was behind the existence of this gas on our neighboring planet, although the authors point out more possibilities: “PH3 could originate from unknown photochemical or geochemical processes or, by analogy with its biological production on Earth, due to the presence of life ”.
In the Earth's atmosphere (with an abundance of parts per trillion on a global scale) this molecule is exclusively associated with anthropogenic or microbial activity, and in the solar system it is found only in thereducing atmospheres of giant planets, where it occurs in deep atmospheric layers at high pressures and temperatures, to then rise upwards by convection.
However, the solid surfaces of therocky planetsThey, like Venus, present a barrier to their interior, and phosphine should be rapidly destroyed in their highly oxidizing crusts and atmospheres.
A marker of possible life
In fact, PH3 has been proposed as a biosignature whose detection could indicate the potential existence of some form of life on these planets, although its observation is complicated since many of its spectral characteristics are strongly absorbed by the Earth's atmosphere.
To solve it, Greaves and his colleagues observed Venus with two of the telescopes best equipped to record submillimeter radiation: theJames Clerk Maxwell telescope and the Atacama Large Millimeter / submillimeter Array (SOUL), in 2017 and 2019 respectively.
In this way they detected a spectral signature that is unique to phosphine and estimated an abundance of 20 parts per billion in the clouds of Venus.
In principle the conditions on the surface of Venus arehostile to life, but the environment of its upper cloud layer, about 53 to 62 km above the surface, is temperate. However, the composition of the cloud masses isvery acidic and, under those conditions, phosphine should also be destroyed very quickly; but there it appears.
'Airborne' microbes on Venus?
Astronomers have speculated for decades about the possible existence of microbes in the high clouds of Venus, microorganisms that would float free from the scorching surface but would need a very high tolerance to acidity. The detection of phosphine could point to such extraterrestrial 'airborne' life as a possibility.
The authors have analyzed different ways that PH3 could be produced, including possible sources on the planet's surface, volcanism, micrometeorites, lightning or chemical processes that are occurring within the clouds. At the moment they have not been able to determine what generates the traces of phosphine.
Although they do not totally rule it out in their study, the authors argue that its detectiondoes not constitute solid evidence of microbial life and it only indicates that potentially unknown geological or chemical processes are occurring in our neighbor.
The team points out that more observations and models are needed to study the origin of this gas in the atmosphere of Venus and that other spectral characteristics of PH3 should be sought, in addition to suggesting that a samplingin situ in its clouds and surface it would allow to closely examine the sources of this gas and solve the mystery.
Jane Graves et al. "Phosphine gas in the cloud decks of Venus".Nature Astronomy, September 14, 2020.