A team led by @jgreaves6 have found what might be signs of life high in Venus' atmosphere. They have detected phospine, a gas which on Earth is produced only by life, in quantities they say are too large to be produced any other way. (1/17)

The discovery was made by using sub-mm (microwave) telescopes @eao_jcmt and @almaobs; phosphine is detected roughly 50km above the surface; parts of the atmosphere have temperature and pressure similar to sea level on Earth (2/17)

The phosphine exists at about 20 parts per billion, which doesn't sound much but which the team's modelling says is ten thousand times more than can be produced by volcanic activity or atmospheric chemistry. Their conclusion - this could be life. (3/17)

Is this real? Firstly, I'm told there has been much skepticism, including from journal referees, about the detection. JCMT and Alma were not made to look at things as bright as Venus and this is a difficult observation. (4/17)

However, we have detections from two seperate telescopes, and the team who led the data reduction - @jgreaves6 and Anita Richards at @UoMPhysics - know JCMT and Alma very well. I'd bet the detection is real. (5/17)

(Side note - @planetarycolin reminded me yesterday that the Russian Vega descent probes found - confusingly - that the lower clouds of Venus had lots of Phosphorus. They didn't test its form, and people assumed it would be phosphoric acid, not phosphine) (6/17)

Is phospine a sign of life? It's only produced by life - in strange places like penguin guts - on Earth, and though its seen in the atmospheres of Jupiter and Saturn there its created by pressure-driven chemistry that can't be happening on Venus. (7/17)

The team - particularly William Bains, along with Helen Fraser at the OU and others - have built a model that tries to keep track of the many chemical reactions that might produce phospine. They can't get it to account for what's seen. (8/17)

The details of that model are in a second paper which has not yet been accepted by the journal, and it will be heavily scrutinised when it comes out! There are two possibilities. Either the team have missed something obvious or made a mistake... (9/17)

..Or studying the chemistry of Venus' atmosphere just became a very hot topic. Reactions in a sulphuric acid rich environment are, I suspect, not well understood. It will be fascinating to watch what happens. My bet is on chemistry ( #itsneveraliens) but who knows! (10/17)

(Worth noting that my go-to expert on solar system chemistry @PlanetDr is highly skeptical, and posted this earlier, which is wise: https://twitter.com/PlanetDr/status/1305181092522201094) (11/17)

If it is life, it must be very unusual life. There are microorganisms adapted to very acidic environments on Earth, but nothing like this. There are also ideas about how a life cycle could work, published by @profsaraseager's team: https://www.discovermagazine.com/the-sciences/how-floating-microbes-could-live-in-the-acid-clouds-of-venus (12/17)

If it is life, then the prospects of life being widespread in the cosmos increases rapidly. If life can evolve and survive on Venus, I suspect we should expect it in a much wider range of environments than previously thought. (13/17)

So what's next? I'm sure there will be repeated observations. Understanding if the detection is real, and whether the amount of phospine changes with time will be crucial. (14/17)

What about spacecraft? None of the planned orbiters will have instruments which will help. Proposed entry probes (American DAVINCI+, Russian Venera-D) will measure the composition but will plunge through the atmopshere fast. (15/17)

What's needed is something like the proposed Venus Flagship Mission which would have a balloon floating in the atmosphere, capable of looking for biomolecules. Balloning on Venus (though probably in the 2030s)! https://vfm.jpl.nasa.gov  (16/17).

So there's much work to do to understand what this result means, but it's fascinating. If you're in the UK, you can hear the full story from @jgreaves6 and her team on #skyatnight, BBC4, 10.30pm tonight (17/17)

One final thing - I've been trying to think how this compares to other moments. I think what's different here is that the team went looking for phospine in order to search for life - and found it. That's a remarkable result whichever way you look at it (18/17)

(A certain vintage of British astronomer will be pleased to know that one version of the story of how this discovery came about features conversations in Uncle Billy's in Hilo). (19/17)

I'm looking forward to the flood of people with theories about making phosphine - mine is chemistry kicked off by high energy particles from the solar wind, which can penetrate into the dense Venusian atmosphere.