Mercury, which has no moons, is the smallest planet in the solar system and, like Venus, Earth, and Mars, is a terrestrial planet. With a diameter of 4,880 km, it is larger than Earth’s Moon but smaller than the largest moons of Jupiter and Saturn.
Orbiting the Sun in a highly elliptical path, Mercury completes one revolution in 88 days and, with an average distance from the Sun of 58 million km, is the planet closest to the Sun and the fastest-moving. Because of its high orbital speed, the Romans associated Mercury with the messenger of the gods (Greek: Hermes) and often depicted him with winged feet.
With its heavily cratered surface, Mercury closely resembles the Moon. It rotates three times on its axis during two orbits around the Sun. Because of its low gravity, it cannot retain an atmosphere that could help balance temperatures between the day and night sides. As a result, surface temperatures range from 430 °C on the day side to minus 170 °C on the night side.
A rocky planet with many craters
0
0.055 Earth masses
4,879 km (scale: 1.1 mm)
87 days, 23 hours, 15 minutes
58 days, 15 hours, 36 minutes
0.034 degrees
clockwise (like a train loop)
9,123 watts/m²
1.38 degrees
virtually nonexistent, since it is too low in mass
not real weather
1983 Mariner 10 (U.S.)
