Could Venus possibly harbor life?

Two recently published papers, including one in Nature Astronomy (about the discovery itself) and this one in Astrobiology (describing a possible life cycle), report the existence of phosphine in the upper atmosphere of Venus, a gas that cannot be easily generated by non-biological processes in the conditions believed to exist in that planet. Phosphine may, indeed, turn out to be a biosignature, an indicator of the possible existence of micro-organisms in a planet that was considered, up to now, barren. Search for life in our solar system has been concentrated in other bodies, more likely to host micro-organisms, like Mars of the icy moons of outer planets.

The findings have been reported in many media outlets, including the NY Times and The Economist, raising interesting questions about the prevalence of life in the universe and the possible existence of life in one of our nearest neighbor planets. If the biological origin of phosphine were to be confirmed, it would qualify as the discovery of the century, maybe the most important discovery in the history of science! We are, however, far from that point. A number of things may make this finding another false alarm. Still, it is quite exciting that what has been considered a possible sign of life has been found so close to us and even a negative result would increase our knowledge about the chemical processes that generate this compound until now believed to be a reliable biomarker.

This turns out to be a first step, not a final result. Quoting from the Nature Astronomy paper:

Even if confirmed, we emphasize that the detection of PH3 is not robust evidence for life, only for anomalous and unexplained chemistry. There are substantial conceptual problems for the idea of life in Venus’s clouds—the environment is extremely dehydrating as well as hyperacidic. However, we have ruled out many chemical routes to PH3, with the most likely ones falling short by four to eight orders of magnitude (Extended Data Fig. 10). To further discriminate between unknown photochemical and/or geological processes as the source of Venusian PH3, or to determine whether there is life in the clouds of Venus, substantial modelling and experimentation will be important. Ultimately, a solution could come from revisiting Venus for in situ measurements or aerosol return.

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