Pretty much as the title; let’s define ‘extraterrestrial’ as tracing its ultimate origin to a planet other than Earth, ‘life’ as possessing physiological functions.
For ‘human’ let’s stick with the old school species definition; something can can produce viable offspring with a human around today. I know there are…problems with this definition, but if we speciate into Morlocks and Eloi which cannot produce viable offspring with a human around today, no dice. Likewise super-intelligent cyborgs, brains in vats, digital consciousness and other trans-human malarky need not apply.
Divided the poll into spacefaring (having vehicles capable of traveling beyond planetary atmosphere) and non-spacefaring (was going to say ‘intelligent and not intelligent’, but we’re already drowning in definitional uncertainty), and ‘evidence of’ and ‘contact with’ - basically is it still alive or not when we find it. So if we find a fossilised space-cow on Aldebaran III that would be evidence of non-spacefaring life, if we bump into the vanguard ships of Grak the Indefatigable inter-galactic empire that’s contact with space-faring.
Poll incoming, split it into probability by percentage - 0% if you think we’ll definitely be extinct or the distances just too vast, 100% if you think it’s an absolute certainty, 50% is the coin-flip. Also included an option if you think we’ve already come into contact with/have evidence of extraterrestrial life and, like, the government’s covered it up man, wake up sheeple!
I would give even odds of finding some kind of existing primitive life within our solar system (more likely Europa, Ganymede, Titan, Enceladus, or Triton than Mars or Venus) at even odds. The ready availability of amino acids and liquid medium on those moons provides the basis for life as we know it (based upon carbon-nitrogen structures) and there is nothing we’ve seen about life on Earth that would make it appear to be unique in composition or chemical mechanics.
As for life beyond our solar system, I don’t think there can be any credible guess. Just the possibility of being able to travel to other stars in embodied form is doubtful, and the converse applies equally. Short of some kind of science fictional wormhole or superluminal propulsion, sending natural organisms between stars is improbable, and we would expect such exploration to be done by some kind proxy.
Let’s see–for evidence of non-spacefaring ETs, I went with 40 percent, mainly through telescopic measurements of the atmospheres of exoplanets. For contact with non-spacefaring ETs, I put 20 percent, for the chance that there is some sort of microbial life on one of the moons or minor planets in our solar system that contain liquid water (or possibly Mars.) For evidence of spacefaring ETs, I gave 10 percent, again for telescopic evidence of their presence in some other solar system. For contact with spacefaring ETs, I put it at 0 percent–space is too big and travel/communications too hard to make it likely within the remaining lifetime of our technological civilization.
I bet we’ve had contact with life that has traveled through space but more at the microbial rather than sentient level. Heck, a couple cells /microbes hitching on some rock? No question.
Yeah – that isn’t what you were asking. But since some of what’s here now may show its roots elsewhere, I’m going with it.
My take: IF the Romulans, the Corellians, the Tralfmadorians or the Killer Klowns are out there, they’re so far away we’ll never communicate with them.
Reasonable odds (I put 50%) of finding evidence of, and “encountering”, non-spacefaring life – as others have said, I think that there’s a fair chance that we’ll find some manner of primitive (i.e., non-intelligent) life somewhere in our solar system.
Odds of us finding evidence of (much less encountering) spacefaring extraterrestrial life (i.e., something intelligent and capable of communication and space travel, not just a microbe that hitched a ride on an asteroid) are incredibly small. I put 0%, because the odds are much closer to 0% than 10%.