Authors: Jane S. Greaves, Anita M. S. Richards, William Bains, Paul B. Rimmer, Hideo Sagawa, David L. Clements, Sara Seager, Janusz J. Petkowski, Clara Sousa-Silva, Sukrit Ranjan, Emily Drabek-Maunder, Helen J. Fraser, Annabel Cartwright, Ingo Mueller-Wodarg, Zhuchang Zhan, Per Friberg, Iain Coulson, E’lisa Lee, Jim Hoge
Studying the atmosphere of the planets in the Solar system can have many applications. Not only does it simply provide information about the features of each planet and what chemical processes take place there, but it can also help us understand the geochemistry of our own planet. Another application of such atmosphere analysis is the search for the possible presence of life outside the Earth. There are multiple indicators of the presence of organic forms or living organisms. Most well known are the traces of carbon compounds or traces of water. Another useful indicator is the phosphine gas, PH3. This gas is usually produced by certain microorganisms, and can rarely be produced without their presence. It can also be quickly destroyed on the planet’s surface. It was previously found outside Earth in the deep layers of atmospheres of giant planets, where very high pressures are present.
A team of astronomers at Cambridge has developed an approach to detect PH3 in an atmosphere of the planet, called PH3 1-0 mm rotational transition at the 1, 123 mm wavelength. To calibrate their approach, the astronomers analysed Venus' atmosphere with the help of the James Clerk Maxwell Telescope (JCMT), in June 2017. The researchers did not expect to find any phosphine gas at all. Instead, they have detected PH3 at considerable amounts.
At first, the researchers thought their findings to be an artifact, possibly caused by another molecule with similar parameters. To confirm this suspicion, they have used another tool called the Atacama Large Millimeter/submillimeter Array (ALMA) in 2019. They have taken multiple measures to decrease the possible contamination or cross-detection of other molecules.
Surprisingly, analysis with the ALMA has confirmed that there was indeed phosphine gas present, though in considerably lower amounts compared to Earth's atmosphere. No other molecules could cause a similar result. It was also found that PH3 is particularly abundant in the middle altitudes, in the cloud decks of the atmosphere. The levels of the gas were significantly lower in the polar regions of the planet. Incidentally, PH3 can be also found in similar areas on Earth, as some microbial communities that produce phosphine gas can be found there.
At our current knowledge, no possible ways to produce phosphine gas are present in Venus. The specialists propose that PH3 was either produced through a chemical process currently unknown to our science, or there is indeed a life form that can generate it. Only more thorough analysis and possibly the use of probes could provide a clearer answer to this mystery.
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