Alien is every thing thats extratrrestrial not from this wrold.Even in our own solar system some of planets are so alien and different from are own planet Earth like Venus the acid hell hole,Mars the dust devil there are like hurricans here,Mercury the two faced planet and the 4 colassal gas giants.But there are many more bigger and smaller planets,suns,stars & galaxys out there.We are very fortunet to be in the right spot with right size sun for live to begin.The universe is so big why not live to begin on a nother wrold.Edit