So just to pick-up on the discussion about alien civilisations - The Drake Equation attempts to quantify the number of advanced civilisations that might exist across the entire universe - but most of the values for the equation’s variables are, currently, not accurately (empirically) known and so the whole exercise is really just a ‘tool for thinking’; that is to say it helps us think about the right things as we try to assess if there are other civilisations out there and, if so, how many there might be - it’s very tempting to say that, statistically, in an infinite universe, there must be infinite advanced civilisations - but then when you look at humanity and our home planet, there is a very long list of very unlikely events that had to happen before we could evolve - and we (humans) therefore seem to be, statistically, extremely unlikely…….. the truth is, right now, we have no idea - we might be completely alone - or the universe might team with intelligent life  - and both possibilities seem equally amazing to me…….. But, if we can find evidence of life - any sort of life - on another planet or satellite or any place off this Earth, then the odds tip massively in favour of there being intelligent life out there somewhere………..  But, even then, the distances and timescales and hazards involved probably mean that, even at the SOL, we are never going to go there and they are never coming here - And even communication across those vast distances is probably impossible for the same reason - And it might be that our existences don’t even overlap - modern humans have only existed for approximately 200K years which is a tiny window of opportunity in the context of cosmological time - we have to think in terms of, not just elsewhere but also ‘elsewhen’ - other advanced civilisations might have been and gone and others might be yet to come……….  IMHO :)