While it’s far too soon to claim that life has been discovered beyond our planet, a new scientific discovery provides a tantalizing clue that Venus may be the best place to search for extraterrestrial life. The Royal Astronomical Society announced today that phosphine molecules have been observed from Earth in the atmosphere of Venus.

Why does that matter? The phosphine molecule is created either artificially on Earth or “by microbes that thrive in oxygen-free environments,” as RAS describes.

An international team of astronomers, led by Professor Jane Greaves of Cardiff University, today announced the discovery of a rare molecule — phosphine — in the clouds of Venus. […]

Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes — floating free of the scorching surface, but still needing to tolerate very high acidity. The detection of phosphine molecules, which consist of hydrogen and phosphorus, could point to this extra-terrestrial ‘aerial’ life. 

While the surface of Venus is far too hot to support life as we know it on Venus, scientists haven’t ruled out life in the clouds of Venus being the source of the phosphine molecules. What scientists have ruled out thus far are other sources for the molecules like lightning, sunlight, and volcanic activity due to the amount of molecules observed.

But before we can begin to claim that the atmosphere of Venus is the first known environment to support life beyond Earth, a tremendous amount of investigation is required. NASA has two potential missions focused on studying Venus, and small satellite launch provider Rocket Lab has already expressed interest in a commercial mission in the next three years.

From the paper:

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 phos- phine (PH3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH3 at ~20 ppb abundance is inferred. The presence of PH3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and sub- surface, or from lightning, volcanic or meteoritic delivery. PH3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH3 on Earth, from the presence of life. Other PH3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas.

The full paper is available to read for free on Nature Astronomy.

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