The question of whether all planets are named after gods has a complex answer rooted in the history of astronomy and language. Most of the eight major planets in our solar system bear names derived from ancient Roman and Greek mythology. However, this naming convention is not universally applied, with one significant exception. This tradition was set by the five classical planets visible to the naked eye, a convention that later astronomers intentionally continued for newly discovered worlds.
The Classical Planets and Roman Mythology
The five planets known since antiquity—Mercury, Venus, Mars, Jupiter, and Saturn—were named by the Romans after their principal gods and goddesses. This system arose from observations of the planets’ apparent characteristics in the night sky. The Romans inherited this practice from the Greeks, who associated these moving lights with their own pantheon.
Mercury was named after the Roman messenger god due to its swift movement across the sky, reflecting the god’s speed. Venus, the brightest object after the Sun and Moon, was associated with the Roman goddess of love and beauty. Mars was named after the Roman god of war because its reddish hue evoked images of blood and fire.
Jupiter, the largest planet, was named for Jupiter, the king of the Roman gods. Saturn, the most distant classical planet, was named after the god of agriculture and time, reflecting its slower movement. This mythological theme laid the foundation for the naming of every subsequent planetary discovery.
The Post-Telescopic Discoveries
The tradition of using mythological names continued after the invention of the telescope allowed for the discovery of new planets. Uranus, the first planet discovered in the modern era by William Herschel in 1781, initially had a different proposed name. Herschel suggested naming it Georgium Sidus (George’s Star) in honor of his patron, King George III.
This suggestion was not popular outside of Great Britain, and astronomers sought a name that would align with the existing mythological scheme. German astronomer Johann Elert Bode proposed Uranus, the Latinized version of Ouranos, the Greek god of the sky and the father of Saturn. The name Uranus was eventually accepted to maintain the mythological consistency of the solar system.
Neptune, discovered in 1846 following mathematical predictions, was named after the Roman god of the sea. Astronomers made this choice to preserve the consistent mythological theme. The naming of Uranus and Neptune represented a transition from ancient observation-based naming to a formal, consensus-driven process that upheld the mythological tradition.
The Unique Case of Earth
The definitive exception to the mythological naming convention is Earth. It is the only major planet not named after a Greek or Roman deity. The name Earth has a much older, non-mythological origin rooted in language.
The modern English word “Earth” derives from the Old English word eorþe, which has cognates in every Germanic language. This word traces back to a Proto-Germanic term meaning “the ground that you walk on” or “soil.” The name is descriptive, simply signifying the ground or the world itself.
This etymology reflects a time when ancient cultures did not view the ground beneath their feet as a planet, but simply as their world. While the Romans had goddesses like Tellus or Terra, who represented the fertile land, the planet itself was not formally designated with a divine name like its neighbors. The name Earth stands alone, a testament to its linguistic origins as “the ground.”