We have plenty of evidence for aliens. Take into consideration that this planet is not "perfect" for life, but its factors are set to that life can arise. If the Earth were smaller or closer to the Sun by a few hundred thousand miles, life would still have arisen. We are just off the center of the "habitable zone" of out solar system. Every system has a "habitable zone", and if a planet falls within this zone, it can produce life.
So really the evidence is in our understanding of the universe. Just as we have evidence for our Sun, we are able to spot other stars and tell if a spot in the night sky is a planet or a star. We see that life has arisen on this planet, so given our knowledge of the universe, it seems likely that there are planets out there that can support life.
So really the evidence is in our understanding of the universe. Just as we have evidence for our Sun, we are able to spot other stars and tell if a spot in the night sky is a planet or a star. We see that life has arisen on this planet, so given our knowledge of the universe, it seems likely that there are planets out there that can support life.
