The story behind the names of the planets was written long ago by early stargazers - the first astronomers to focus attention on the sun, the moon, and the visible planets Mercury, Venus, Mars, Jupiter, and Saturn. They believed that each of these celestial bodies influenced a particular day of the week. Diverse cultures ascribed the names of their gods to individual planets (with the notable exception of Earth).
The Romans matched planetary attributes with particular deities and named the known planets accordingly. Tiny Mercury was named after the fleet-footed messenger to the gods, probably because it moves so quickly across the sky; Venus, the brightest planet visible to the unaided eye, was named for the goddess of love and beauty. Jupiter, more than twice as massive as all the other planets combined, earned the name of the superior god.
These Roman names were adapted by early European astronomers and have persisted, long after the ancient geocentric model of our solar system was proven wrong.