Mercury is the smallest planet in our solar system and the one closest to the Sun, orbiting at an average distance of about 58 million kilometers (36 million miles). Despite being so close to the Sun, Mercury is not the hottest planet—Venus holds that title—because Mercury lacks a substantial atmosphere to trap heat. This thin exosphere, made mostly of oxygen, sodium, hydrogen, helium, and potassium, cannot protect it from extreme temperature changes, causing daytime temperatures to soar to around 430°C (800°F) and nighttime temperatures to plummet to -180°C (-290°F). Mercury’s surface is heavily cratered, resembling Earth’s Moon, due to billions of years of impacts from asteroids and comets. It has a large iron-rich core that makes up about 85% of its radius, giving it a strong but short-lived magnetic field. A Mercury year is just 88 Earth days, but a single Mercury day (sunrise to sunrise) lasts about 176 Earth days due to its slow rotation and orbital resonance. With no moons or rings, Mercury remains a solitary and mysterious world. Spacecraft such as Mariner 10 and MESSENGER have provided detailed images and data, revealing evidence of water ice in permanently shadowed craters near its poles, protected from the Sun’s heat. Scientists believe Mercury’s formation and geology hold important clues about the early solar system, making it a fascinating object of study despite its small size and harsh environment.