When we see sky at night , we feel someone is watching us. This is thought that validate existance of aliens . We feel "we are not alone in this whole mysterious universe ". The life which appears to be so simple externally is more complex as we research deeper and deeper. Certain theory says " humans are just seed of aliens experiment". They visit on this blue planet timely to see their experimental conclusion. Might this can also be true , the aliens have chosen this planet for their experiment because of blue color of earth as seen from outer space.