[jrd259]

I think finding life on any other world would be very exciting even if uni-cellular. While we know which organic compounds are common in the nearby universe, we have no idea what other "architectures" are feasible, even granted an environment (temperature, pressure, solar spectrum) roughly like ours (including extremophiles). Life optimizes, but it's also path-dependent. Surely Earth's genetic code is accidental and path-dependent, but how constrained is the protein design space? For example, given a star like ours, do we have optimum chlorophyll? Or if you make your living as a sulfate reducing prokaryote, how many different ways can you do that?

No telescope will tell us what the ribosomes of Barnard b look like, of course.

But if only macroscopic life excites you, is it clear that you need eukaryotes for complex (multi-cellular) life? And how can you know it happened only once? It could also be that it happened multiple times, but one strain outcompeted (or just ate) every other. There could be undiscovered alternate "eukaryotes" if they remained single-cellular, too.

[millstone]

Why fixate on life at all? Would inorganic intelligent robots be a boring discovery?

[adrianN]

I think most people would classify most things as life if they reproduce and have a metabolism.