[cygx]

abiotic pathways ruled out

To the best of the reasearchers' knowledge: All known pathways to produce phosphane couldn't explain the observation (they were talking several orders of magnitude off). Abiotic 'exotic' chemistry is still an option (ie the 'unknown unknown' hasn't been ruled out).

[jandrese]

Humans don't have nearly as much experience dealing with conditions like we find on Venus, so it's entirely possible this is a yet-unknown chemical reaction. Most chemists don't like dealing with blazing hot highly pressurized strong acids all day long.

[tantalor]

You don't need to state the obvious.

It's impossible to rule out an "unknown unknown" by definition, because if you did then it wouldn't be "unknown" anymore.

[cygx]

No-go theorems exist (conservation of energy for example, hence no perpetual motion machines). Instead, they tediously had to exclude any process they could think of one by one.

[formerly_proven]

> No-go theorems exist

That's K-K, not U-U.

[cygx]

There are known abiotic pathways. They've been ruled out.

There are unknown biotic pathways known to exist (from the press conference, biotic phosphane production on earth apparently still has some large question marks attached?).

There might be unknown abiotic pathways ('unknown unknowns'). In principle, there could be some clever way to rule them out based on the constraints of the Venusian environment.