Mercury is the smallest and closest to the Sun of the eight planets in the Solar System, with an orbital period of about 88 Earth days. Seen from Earth, it appears to move around its orbit in about 116 days, which is much faster than any other planet in the Solar System. It has no known natural satellites. The planet is named after the Roman deity Mercury, the messenger to the gods.
| Diameter | 4,880 km |
| Mass | 3.30e23 kg |
| Temperature | 80 K (-193 °C) to 700 K (427 °C) |
| Composition | Percentage |
|---|---|
| Oxygen | 42.0% |
| Sodium | 29.0% |
| Hydrogen | 22.0% |
| Helium | 6.0% |
| Potassium | 0.5% |
| Argon, nitrogen, carbon dioxide, water vapour, xenon, krypton, and neon | Trace amounts |
Mercury is the smallest planet in the Solar System
Mercury is only the second hottest planet. Despite being further from the Sun, Venus experiences higher temperatures. The surface of Mercury which faces the Sun sees temperatures of up to 427°C, whilst on the alternate side this can be as low as -173°C. This is due to the planet having no atmosphere to help regulate the temperature.