Mercury

Planet Mercury: Geography, Distance from the Sun, and Key Features

Mercury is the smallest planet in our solar system and the one closest to the Sun. Named after the swift-footed Roman messenger god, it moves faster in its orbit than any other planet, completing one revolution around the Sun in just 88 Earth days. Because of this rapid orbit, Mercury was known to ancient civilizations as both a “morning star” and an “evening star,” appearing briefly before sunrise or after sunset.

Distance from the Sun
On average, Mercury lies about 57.9 million kilometers (36 million miles) from the Sun. This proximity means it receives more than six times the solar energy Earth does. However, despite being so close, Mercury is not the hottest planet—Venus holds that title—because Mercury has almost no atmosphere to trap heat.

Geography and Surface Features
Mercury’s surface is heavily cratered, resembling Earth’s Moon. This rugged terrain is a result of billions of years of impacts from meteoroids and comets. Between these craters lie vast plains, some formed by ancient volcanic activity. The largest known impact basin, the Caloris Basin, is about 1,550 kilometers (960 miles) across and was created by a massive collision early in the planet’s history.

A notable geological feature is Mercury’s network of lobate scarps, or giant cliff-like structures, which formed as the planet’s core cooled and contracted, causing the crust to buckle. These scarps can stretch hundreds of kilometers and rise several kilometers high. Mercury’s high density—second only to Earth—suggests a large metallic core, making up about 85% of its radius.

Extreme Temperatures
With virtually no atmosphere to distribute heat, Mercury experiences the most dramatic temperature swings of any planet. Daytime temperatures can soar to 430°C (800°F), while nighttime temperatures plunge to –180°C (–290°F). This makes its surface an extreme environment for any potential lander or probe.

Rotation and Orbit
Mercury’s rotation is unusual. It takes about 59 Earth days to spin once on its axis, but because of its 88-day orbital period, a day on Mercury (sunrise to sunrise) lasts 176 Earth days. This results from a 3:2 spin-orbit resonance, meaning Mercury rotates exactly three times for every two trips around the Sun.

Atmosphere and Magnetic Field
Mercury has an extremely thin exosphere composed mostly of oxygen, sodium, hydrogen, helium, and potassium. It’s so sparse that individual molecules rarely collide. Despite its small size, Mercury has a surprisingly strong magnetic field—about 1% as strong as Earth’s—likely generated by a partially molten iron core.

Exploration
The planet has been visited by only two spacecraft: NASA’s Mariner 10 in the 1970s, which mapped about 45% of the surface, and MESSENGER, which orbited Mercury from 2011 to 2015 and provided detailed maps and data on its composition, geology, and magnetic field.

Conclusion
Mercury is a planet of extremes—small yet dense, close to the Sun yet possessing frigid nights, geologically ancient yet still shrinking. Studying it helps scientists understand the early history of our solar system, the processes shaping terrestrial planets, and the conditions near our star.