What kind of extraterrestrial life are we talking about here? Would microorganisms be sufficient?

And what level of proof are we after? We could pick up molecular composition that is chemically highly unlikely in the absence of life in distant planetary atmospheres, for example?

@JonWharf Yes, microorganisms would be sufficient - and probably the most likely.

@JonWharf And I’m going to go with mainstream scientific consensus that it is proof of life, I will defer to the experts. No fringe theories though.