Let's face it, finding life in the solar system elsewhere than on Earth will be difficult at best.
Mercury : not an option
Venus : hellish
Earth : perfect
Moon : maybe some very tough bacteriaes from space probes contamination.
Mars : maybe in the past, fossiles could be a thing. Nowadays ? Unlikely : no magnetosphere, real cold. Still best candidate for me.
Europa : very cold, probably water but no light under the ice. We need to know more : how much heat the core can generate, do tidal forces generate a lot of friction...
Titan : very very cold, sunlight extremely dim. Methane-based chemistry. More than unlikely.
Now of course heavier-than-air flying was unlikely in the 19th century. We have to keep searching (which involves funding science) and hope to have nice surprises, else build some certainty that we're alone there.