Mercury: The Smallest and Swiftest Planet

Mercury is the smallest planet in our solar system and the closest to the Sun. Named after the Roman messenger god known for his speed, Mercury lives up to its namesake by completing an orbit around the Sun in just 88 Earth days—the shortest orbital period of any planet.

Physical Characteristics

Despite being the smallest planet (only slightly larger than Earth's Moon), Mercury is incredibly dense, with a large iron core making up about 75% of its radius. Its surface is heavily cratered, resembling our Moon, with vast plains and towering cliffs called scarps that formed as the planet cooled and contracted over billions of years.

Extreme Temperatures

Mercury experiences the most extreme temperature variations of any planet in the solar system. During the day, temperatures can soar to 800°F (430°C), while at night they plummet to -290°F (-180°C). This dramatic swing occurs because Mercury has virtually no atmosphere to retain heat.

Exploration

Mercury has been visited by only two spacecraft: NASA's Mariner 10 in the 1970s and the MESSENGER mission, which orbited Mercury from 2011 to 2015. These missions revealed surprising discoveries, including evidence of water ice in permanently shadowed craters near the poles.