europa is a dead planet (moon)
the core isn't making heat and so under the ice there is nothing that could feed these creatures. nothing comes from above due to the ice. and nothing comes from under due to it being a dead planet (moon)
It's possible that the gravitational pull on the moon stretches and squashes the interior heating it up inside, creating hydrothermal vents that could feed the development of life. We currently don't have enough information to rule it out just yet. Unless there has been a new discovery that I'm not aware of.
The age of the universe is tremendous and the sun is a relatively young star.
Actually it's a middle ages star.
That means it still has about another 4.5 billion years, give or take a billion.
Aliens exist simply by the fact that what i said above. People from early cultures spoke of the Annunaki (a.k.a aliens) I'm not saying they're true but I don't see any motives for them to lie.
Pretty much in the same category as farmers who report being **** probed by aliens.
While it's likely life exists on another planet and even likely there is life with equivalent capabilities to our own, there is nothing indicating visitation.
However, concluding from the finite number of planets able to host life in our universe (ignoring any possibility that there may be other universes out there), the probability that there is an alien species that
- is sentient and comparable to us in intelligence
- exists on the same time than we do
is infinitesimal, or at least I consider it that way. Our existence is a micro-flash in the story of the universe, supposing such flashes occur in regular yet rather big intervals, probability that two flashes occur on the same time is so short..
This is all of course very speculative as I (we) don't have any numbers or such to base my opinion on..
I don't know, I think the odds are good that there could be at least one other in our galaxy.
"An estimate is made of the number of habitable planets in the Galaxy, based upon conservative grounds. That is, the number of stars in the disk of the Galaxy that are similar to the sun, and the probability that these stars have a planet in orbit about them with properties similar to the earth, are estimated. The restrictions applied give values of 10 million habitable planets in the Galaxy (mean separation about 110 light years) and 4-1/2 million planets orbiting stars of sufficient age for intelligent life to have formed (mean separation about 140 light years)."
http://adsabs.harvard.edu/abs/1978JBIS...31..411B