And by alien I mean any kind of life, it doesn't have to be sentient.
Personally, I think Europa or Mars might have microbes somewhere.
we should go explore Titan
we should bring all the biomass with us that we can carry, to Titan!
ALL THESE WORLDS ARE YOURS EXCEPT EUROPA. ATTEMPT NO LANDINGS THERE. USE THEM TOGETHER. USE THEM IN PEACE.
Nibiru always makes me think of some unhinged youtube rant about it years ago that kept flashing the words "Nephalim Flesh" on screen.
I think there's a good chance of microbes on on Europa and maybe in some martian aquifer. Other than that I doubt it unless there's some sort of life form that can live in gas giants.
I want a mission to Europa
Not because I think it's the most likely to have life, but because it's my favorite
The clouds of Venus. Could be lots of micro-organisms there.
Earth. If there's any aliens in the Solar system, they can clearly hide from us pretty well, and I'm not really sure what they'd be interested in on any other planet...