Diameter: 4879.4 km
Mass: 0.055 Earths
Composition: Rocky: metals & silicates
Atmosphere: Trace: oxygen, sodium & hydrogen
Surface Temperature: -173 to 427 °C
Year length: 88 Earth days
Day length: 176 Earth days
- With its rocky surface, Mercury is one of the four “terrestrial” planets.
- Like the moon, Mercury’s surface has heavy cratering. This suggests a geological inactivity for billions of years.
- Mariner 10 became the first spacecraft to visit Mercury in 1974, taking images of its surface.
- The second mission to Mercury was completed by the MESSENGER probe much later, in 2008.
- An anonymous Assyrian astronomer (around 1400 BC) holds the title of the earliest known observer of Mercury.
- The Babylonians are also known to have recorded the planet Mercury around 1000 BC.
- The Romans named the planet after their messenger god “Mercury”, while the Babylonians similarly named it after their messenger “Nabu”. The ancient Greeks called Mercury “Apollo” in the morning and “Hermes” in the evening coming to understand it as the same planetary body around 400 BC.