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So #phosphine/phosphane/PH3 was found in the atmosphere of Venus and people are speculating whether this implies the existence of microbial life in Venus& #39;s atmosphere. What& #39;s the chemistry behind this? I& #39;ll try to explain in a way that& #39;s also understandable for non-chemists 1/13
One Earth, the most common phosphorus (P) compounds contain oxygen, like phosphate, which is present in many minerals and also seawater and fresh water. P compounds without oxygen are pretty reactive in an oxygen atmosphere. 2/13
Elementary P and also PH3 have the hazard warnings flammable, toxic, corrosive, and environmental hazard. Dangerous stuff for most Earthlings! 3/13
How do we synthesize PH3? Under oxygen-free conditions, you can put elementary P (or certain other P-containing compounds) and molecular hydrogen (H2) together. Above a certain temperature (>800 K), the chemical equilibrium favors the formation of PH3. 4/13
This happens, for example, in the atmospheres of Jupiter and Saturn, where PH3 was also detected. There& #39;s more than enough H2 and at a certain altitude, the temperature is high enough. 5/13
BUT: On Earth, we can also find traces of PH3 in certain oxygen-poor environments where it is produced by anaerobic bacteria from environmental phosphorus at reasonable temperatures. How do they do it? 6/13
Nobody knows yet, but this is very interesting from a biochemical point of view: Remember that PH3 is very flammable in an oxygen atmosphere? The reaction, leading to phosphoric acid, releases a lot of energy. The reverse reaction *requires* this energy to proceed. 7/13
The generation of PH3 requires either a lot of energy or high temperatures in most (all?) cases we know of, except for that bacterial metabolism. Those bacteria seem to have found another way. 8/13
There are also other photochemical/atmospheric-chemical pathways, but none favor the production of PH3 under the environmental conditions in Venus& #39;s atmosphere. It is simply not hot enough. 9/13
So: All non-bio chemical pathways we know that generate PH3 don& #39;t really work under the conditions in Venus& #39;s atmosphere. The only one we know that is left is the metabolism of anaerobic bacteria. But does that mean that we found an indication for microbial life on Venus? 10/13
All science is based on experience and it& #39;s hard to imagine something we have never experienced. There might be chemical pathways leading to PH3 that we just don& #39;t know yet. But this is a great opportunity for atmospheric chemistry to explore possible alternative pathways! 11/13
It is also a great opportunity for biochemistry to investigate the bacterial metabolism in more detail and figure out the reaction mechanism. This and a thorough investigation of Venus& #39;s atmosphere will allow us to determine whether the PH3 was produced by bacteria or not. 12/13
All in all, this is an exciting discovery, not only for astronomy but also for chemistry! I am looking forward to all the upcoming research inspired by this 
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Sources/further reading:
"Phosphine gas in the cloud decks of Venus": https://www.nature.com/articles/s41550-020-1174-4
"Phosphine">https://www.nature.com/articles/... as a Biosignature Gas in Exoplanet Atmospheres": https://www.liebertpub.com/doi/10.1089/ast.2018.1954
https://www.liebertpub.com/doi/10.10... href=" https://arxiv.org/abs/1910.05224 ">https://arxiv.org/abs/1910....
"Phosphine gas in the cloud decks of Venus": https://www.nature.com/articles/s41550-020-1174-4
"Phosphine">https://www.nature.com/articles/... as a Biosignature Gas in Exoplanet Atmospheres": https://www.liebertpub.com/doi/10.1089/ast.2018.1954
