Hello, friends! When the news came out that phosphine gas had been discovered on Venus, I’m sure we were all thinking the same thing: So what? There’s phosphine on Jupiter and Saturn too. Everybody knows that (don’t they?), and nobody thinks that means Jupiter or Saturn have life.
Fortunately, the authors of this paper from Nature Astronomy address the obvious Jupiter/Saturn issue right away:
[Phosphine] is found elsewhere in the Solar System only in the reducing atmospheres of gas giant planets, where it is produced in deep atmospheric layers at high temperatures and pressures, and dredged upwards by convection. Solid surfaces of rocky planets present a barrier to their interiors, and PH3 would be rapidly destroyed in their highly oxidized crusts and atmospheres.
In other words, it’s very simple for astrophysicists to explain how Jupiter and Saturn make their phosphine. Gas giants with hydrogen-rich atmospheres can do this easily. But how does Venus do it? That’s a much harder question. The only other small, rocky planet with phosphine in its atmosphere is Earth, and we know where Earth’s phosphine comes from: life.
And that is why the discovery of phosphine on Venus is so exciting, while the presence of phosphine on Jupiter and Saturn is no big deal.