Its crater-studded surface is similar in many respects to that of the Moon, forming a desert of dust and rocks where temperatures alternate between scorching hot and freezing cold. Mercury's lack of internal activity means it has been a dead planet for at least 3.6 billion years.
Slightly larger than the Moon, Mercury is a solid sphere formed around a large iron-rich core that makes up 42% of the planet’s volume and nearly 80% of its mass. This could explain Mercury’s particularly high density, making it an exception to the general rule that the bigger a telluric planet is, the greater its density.
Etymology: Mercury was the Roman god of merchants and travellers.|
Discovered: In ancient times, thanks to its star-like brightness.
Distinctive feature: A solar day on Mercury lasts two Mercurian years! This is because Mercury rotates very slowly on its own axis, one of its solar days lasting approximately 6 Earth months.
Typical one-way journey time to Mercury using current technologies: 5 years.
- it has the biggest day-to-night temperature variation in our solar system—from 430°C to –210°C.
- meteorite impacts have left the surface riddled with craters of varying sizes. The largest of these, Caloris Basin, is 1,300 kilometres across and was blasted out by a 100-kilometre-wide asteroid colliding with the planet.
Last updated: May 2003
Solar System Guide, University of Texas McDonald Observatory
Mercury Fact Sheet, National Space Science Data Center (NASA)
Solar System exploration, NASA website
Planetary photojournal - NASA website
CNES Youth/Education site
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