WilliamBains.co.uk

Phosphine and Venus. Venus image courtesy Venus Ultraviolet Imager (UVI). JAXA / ISAS / Akatsuki Project Team

September 2020. Phosphine on Venus! (and why it matters)

On September 14^th Nature Astronomy published a paper by Prof. Jane Greaves and her collaborators, including me, on the discovery of phosphine in the atmosphere of Venus.

This is huge news. Phosphine is a colourless, highly poisonous gas found in tiny amounts (parts per trillion) in Earth's atmosphere. It is a gas that our MIT group has been interested in for some time (see here for a previous news item on this). It is a robust sign of life, as it cannot be made by any geological process: if phosphine is there, it is made by life. On Earth, anyway. See Here for the Greaves et al discovery paper.

So - phosphine on Venus?

We have spent the last two years trying to work out how a non-living process could produce phosphine in Venus' acid, oxygen-rich atmosphere. We calculated the rate at which it might be produced by reaction of atmospheric gases with each other, with sulfur haze, with cloud droplets, with surface rocks. We worked out if volcanoes or lighning or earthquakes or meteorites could account for what Jane saw. We drew a complete blank. There is no way that Venus can make phosphine, unless our understanding of Venus is seriously wrong. This manuscript is the draft of the paper where we go into detail about how we ruled out a wide range of chemical processes as a source of phosphine on the planet.

But life also seems impossible. Life on the surface it ruled out because at surface temperatres - over 400^oC - any organic chemicals are reduced to char. The clouds are cooler, but they are made of sulfuric acid, which destroys nearly every component of life as we know it. Any life on Venus must be radically different from life on Earth, and I do not mean "has pointed ears and green blodo" different. I mean does not use protein. Or DNA. Or maybe even water.

This is spectaculrly exciting because, as Isaac Asimov (probably) said, "The most exciting phrase to hear in science is not "Eureka" but "That's odd...". Something inexplicable, strange, can lead to momentous discoveries. Personally I still think the chance of life on Venus is small. I think the chance of life anywhere is small. But - wow! If that is life, if our nearest neighbour in the Universe, a planet completely unlike ours, hosts living organisms, that would be beyond amazing. The tinyest chance that there is life there is something that we have to follow it up, to go there and find out.

See here and here for the papers announcing the discovery and following up why it is really exciting and inexplicable.