> To do this, they spent the last several years running many species of phosphorous — phosphine’s essential building block — through an exhaustive, theoretical analysis of chemical pathways, under increasingly extreme scenarios, to see whether phosphorous could turn into phosphine in any abiotic way.
> The scientists found that phosphine has no significant false positives, meaning any detection of phosphine is a sure sign of life.
On a first pass through the paper that you linked, I see a couple of instances where they use parameters that directly match conditions on earth. I don't know how well some aspects about Venus are known (e.g. the exact rates at which trace gases are emitted by volcanic activity on Venus).
My personal take on this is that the big claim doesn't seem entirely watertight. And claims like that have been taken apart quite quickly in the past.
Phosphine was detected in Saturn's atmosphere at the Caltech Submillimeter Observatory (right next to the JCMT) decades ago (http://www.ericweisstein.com/research/papers/dps93/). I don't recall anyone screaming "Life on Saturn" back then. I think this is being overhyped.
From the other thread about this, people were saying there are known abiotic chemical pathways to generate Phosphine on gas giants, so detection of Phosphine on Saturn and Jupiter is much less interesting.
Apparently those know pathways don't work on rocky planets, which is why a detection on Venus is more interesting than a detection on Saturn.
I still expect the outcome to eventually be: "we have found a new pathway to Phosphine, that's consistent with a rocky planet", but it definitely seems like a discovery that warrants attention and further study.
Because like a gas giant, the surface is effectively unreachable or at least absolutely uninhabitable (if it even exists for a gas giant). The atmosphere of Venus, like a gas giant, becomes a very hot, supercritical gas as you go deeper. Like a gas giant, the only potential habitable area is in the atmosphere.
Venus still has a sensible surface, although it's unclear if that concept makes sense for a gas giant. "Gas dwarfs" exist, which have a thick atmosphere around a rocky planet (i.e. around Earth's mass), but Venus probably doesn't qualify for that. It's sort of a continuum, though, so the dividing line is somewhat arbitrary.
I think looking at it as a continuum makes some amount of sense, though in this case the authors of the paper seem to have done lots of due diligence in terms of doing the chemistry to check known production paths.
As in, there is known chemistry that produces phosphine at the temperatures and pressures that exist on Saturn and Jupiter, but there is not known chemistry that produces phosphine at the temperatures and pressures that exist on Venus.
So for this particular chemistry, the difference between "gas giant" and "rocky planet" is still a helpful one.
In an colonization sense perhaps, but the environment is very different. Pressures while high on Venus are orders of magnitudes lower than in gas giant atmospheres.
The difference is that Saturn is a gas giant - this discovery relates to the detection of phospine on a rocky planet, which is what makes it unexpected and difficult to explain.
Something along the lines of:
> To do this, they spent the last several years running many species of phosphorous — phosphine’s essential building block — through an exhaustive, theoretical analysis of chemical pathways, under increasingly extreme scenarios, to see whether phosphorous could turn into phosphine in any abiotic way.
> The scientists found that phosphine has no significant false positives, meaning any detection of phosphine is a sure sign of life.