It's a question humanity has pondered for centuries. People have throughout time reported seeing mysterious objects flying in the sky, sightings of little green men, and even being abducted. But is this just the stuff of imagination? Does life exist in outer space? Or are we really all alone?
Detection or contact with an alien life form is not possibleShow moreShow less
The question might be irrelevant since there a no means to identify presence of alien life
With current technology we can only prove if a planet is in a habitable zone but not if it can actually harbour intelligent life.
Possibile method of detecting life on an exoplanet:
- Detection of sign of life on planet (such as river, cities, manufacts) requires an image of planet: this would require an impractical optical resolution of a telescope positioned in the Solar System).
- Sending a probe on an outer solar system is also highly impractical (length of travel).
- Detection of signals form an alien life is impractical (see also SETI argument)
Some missions to our next Solar System can be physically feasible as Breakthrough Starshot 
According to Kardashev scale  level II or III civilisations can be able to harness such high amount of energies that should be detectable on Earth.