Mani, I'm surprised at what you've said, and frankly, pleased, because it seems far more sensible to me than what other Christians on AB have said. They tell us they believe there is no other intelligent life in the universe and that God made the heavens solely for our benefit - to glorify himself, and to enable us to tell the seasons. Can I ask, what makes you believe differently?
To answer the question, bearing in mind what I've said above, I presume the discovery of life on other planets would have a major impact on Christianity.
Where the rest of the world is concerned, if the life discovered was intelligent and technologically advanced, I imagine some of the more potty leaders on this planet (mentioning no names) would immediately see it as a threat and wage war. If that life was not technologically advanced, I imagine those same leaders would wish to conquer and rule the planet. Either way, I think our leaders would handle it badly.
Personally, I can't think of anything more exciting than discovering life in space. How fantastic that would be.