Meaning: It is possible that there are beings from other planets somewhere in the universe.
Choice of Words: Aliens are beings from another planet. Might means it is possible. Somewhere means in a place that is not known.
Alternative Expressions
There's a chance that aliens live somewhere.
Meaning: This sentence suggests that it is possible that there are aliens living in a place that we don't know about.
Choice of Words:Chance means the possibility of something happening. Live means to exist in a particular place. Somewhere refers to a place that is not specifically known or identified.
It's possible that aliens exist on another planet.
Meaning: This sentence suggests that it is possible that there are aliens living on a different planet other than Earth.
Choice of Words:Possible means that something can happen or exist. Planet refers to a large, round object that orbits a star. Another means a different one.