How do we know, alien exist, we don't have any evidence and no substantial reports were made, and so far science have somewhat included aliens in their face books. We know the definition of Science as "Knowledge made my observation and experiment" 'not prediction'- which for now make it intricate for accepting new specimen or discovery made through the light of Science before thorough examination. So, as for now, we know that Alien doesn't exist. I feel pity of the believer who believes that in the end we are going to be abducted by Aliens, Highly intelligent being who's intellect and intelligent transgress ours. Where we can see, in our Holy Scripture e.g the Quran mentions directly that we are the best of Thee Creation. As until now, there is no doubt that our Deity is wrong.

Just reminding the humanity to worship your Lord and praise him for any good occurs and repent and ask for mercy if something wrong occurs.