The closest planet to the Sun, Mercury has been known to humans since time immemorial.
The ancient Babylonians called it Napu, after a Babylonian god, but Mercury owes its modern name to the ancient Greeks and Romans.
Because from Earth Mercury can appear as a morning or evening star, the ancient Greeks originally gave it two names, calling it Apollo when it was visible in the morning and Hermes when it was visible in the evening, both names referencing Greek gods.
Find out more about the planets of the Solar System and how to observe Mercury
But by about 350 BC they’d realised their error (these morning and evening objects were the same planet) and settled on the single name Hermes.
Hermes, in Greek mythology, was the messenger of the gods, so this must have seemed an appropriate moniker for what is by far the fastest planet in the sky, Mercury orbiting the Sun in a mere 88 days.
Hermes’ opposite number in Roman mythology was the god Mercurius, and so as the Greek civilisation slowly ceded influence to the Roman one, the planet became known as Mercurius.
In fact, the Romans named all of the five then-known planets after their deities – see also Venus, Mars, Jupiter and Saturn.
Like Hermes, Mercurius was the messenger of the gods but he was also the god of trade and commerce, which is why his name shares a root with the Latin words merx (goods or merchandise), mercari (to trade) and merces (wages).
Mercurius was later Anglicised to Mercury, giving the planet the name it has today –which in turn inspired the name given to mercury, the metallic element.
Mercury the planet versus mercury the element
Mercury (the metal) was known to the ancient Greeks as ‘hydrargyos’ (“water-silver”), which was Romanized to ‘hydrargyrum’, from which name mercury’s chemical symbol Hg is derived.
For similar reasons – it’s a similar colour to silver, but flows around like water – metal mercury was originally known in English as ‘quicksilver’.
During medieval times, however, alchemists associated each of the seven then-known metals (gold, silver, mercury, copper, iron, lead and tin) with one of the seven then-known planets.
Fast-orbiting Mercury, named after the speedy messenger of the gods, was a natural match for the fast-flowing metal, and so quicksilver became mercury.
So Mercury the planet was named after Mercury the Roman god in ancient times, but mercury the element was named after Mercury the planet far more recently, during the Middle Ages.
Now let’s fast-forward a few centuries… all the way to 2004, when NASA decided to send a second probe to Mercury (the first being Mariner 10, some 30 years earlier).
Casting around for a name for the mission, they came up with the catchy ‘MErcury Surface, Space ENvironment, GEochemistry and Ranging’ – or MESSENGER, for short.
That's how the MESSENGER mission got its name: because it studied the planet Mercury, which was named after the Roman messenger of the gods.
A neat little nod to the long history of a planet that has been fascinating Earth-dwellers for millennia!
