☿Mercury
The smallest and fastest planet, closest to the Sun. A world of extremes where the temperature swing between day and night reaches 600°C.
- Distance from Sun
- 0.39 AU (about 57.9 million km)
- Diameter
- 4,879 km (0.38× Earth)
- Orbital period
- 88 days
- Rotation period
- 58.6 days
- Moons
- None
Science
The scienceMercury is the first planet from the Sun and the smallest in the Solar System. With almost no atmosphere to trap heat, its sunlit day soars to about 430°C, while at night it plunges to -180°C, giving it the largest day-to-night temperature swing of any planet. It races around the Sun in just 88 days, yet its spin is so slow that a Mercurian day (one rotation) lasts longer than its year (one orbit). Its surface is pockmarked with craters like the Moon, and it holds an unusually large iron core for its size.
Name & Myth
The story behind the nameMercury's Western name comes from Mercurius, the winged-sandaled messenger god of Roman mythology (the Greek Hermes), who flew across the sky. Because it circles nearest the Sun and moves fastest across the heavens, it was given the name of "the swiftest god." In the East it was matched to Water among the Five Elements and called "Su-seong," the Water Star.