Greaves, Jane S., Anita M. S. Richards, William Bains, Paul B. Rimmer, Hideo Sagawa, David L. Clements, Sara Seager, et al. 2020. Phosphine Gas in the Cloud Decks of Venus. Nature Astronomy, September. https://doi.org/10.1038/s41550-020-1174-4.
Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine (PH 3) gas in Venuss atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15 Ã) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH 3 at ~20 ppb abundance is inferred. The presence of PH 3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venuss atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. PH 3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH 3 on Earth, from the presence of life. Other PH 3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas.
In reality, as Nick Bostrom pointed out though he in turn adopted the idea from Robin Hanson the finding that life exists on another planet would not be very good news, as it would shift the balance of probabilities to the Great Filter being ahead of us.
But I hope that our Mars probes discover nothing. It would be good news if we find Mars to be sterile. Dead rocks and lifeless sands would lift my spirit.
Conversely, if we discovered traces of some simple, extinct life-formsome bacteria, some algaeit would be bad news. If we found fossils of something more advanced, perhaps something that looked like the remnants of a trilobite or even the skeleton of a small mammal, it would be very bad news. The more complex the life-form we found, the more depressing the news would be. I would find it interesting, certainlybut a bad omen for the future of the human race.
Though in fairness, at least in this case, the severity of such a finding would be mitigated by:
Said life forms probably being prokaryotes, which are far simpler than the eukaryotes which are the prerequisite for the appearance of complex multicellular organisms. (My own view is that it is the prokaryote to eukaryote transition which is by far the best candidate for a past Great Filter). Substantial chance that it arose as a result of biota transfer from Earth (regionalized version of panspermia hypothesis). Freak chance, sure, but there have been ~4 billion years for it to happen.
Nonetheless, even considering that said shift in the weight we assign to the Great Filter being in the future will be very modest, given the literally existential implications of these findings, there should be much more research to:
Ascertain that the phosphites really are produced by life. Get samples of these organisms. Establish whether they evolved independently, or got there from Earth.
This could also be the spur to embark on construction of a Venus space base.
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