> you would have no choice but to assume contamination from human probes as the most likely explanation.
You would have considerable choice; it would be quite obvious whether they'd been on a separate evolutionary trajectory for billions of years or not. That's still the boring outcome, though; not related to us at all would be far more interesting.
Well, we don't know how unlikely it is. It increasingly looks like life showed up on earth almost as soon as it was geologically possible for it to show up, which, if true, would indicate either that abiogenesis is pretty easy or that panspermia is a thing.
It would indicate that, but it's also somewhat expected if we're around to make that observation, which tempers how much information we can take away from it.
However, happening on two adjacent planets would really affect our estimations of the likelihood of abiogenesis.
> It would indicate that, but it's also somewhat expected if we're around to make that observation, which tempers how much information we can take away from it.
Life could have arisen on Earth much later than it did and we could still have been around to see it (or if not us, something like us) so the anthropic principle doesn't apply here. The fact that it arose so early is meaningful.
It is, but it's also sample size of 1. So yes, it indicates something but the confidence interval is really wide. Still, like you point out it's not meaningless as some people do try to argue.
If you take a bayesian approach to the problem it's far more likely that abiogenesis is common. This youtube video does a great job of explaining it: https://youtu.be/iLbbpRYRW5Y
We have basically zero data to tell us whether this outcome is "unlikely" or not. It could very easily turn out that this outcome is overwhelmingly likely.
You would have considerable choice; it would be quite obvious whether they'd been on a separate evolutionary trajectory for billions of years or not. That's still the boring outcome, though; not related to us at all would be far more interesting.