수성, or Mercury, is the closest planet to the Sun in our solar system. It is a small, rocky planet with a diameter of about 4,880 kilometers. Due to its proximity to the Sun, 수성 experiences extreme temperature variations, ranging from very hot during the day to extremely cold at night. The surface of 수성 is covered with craters, similar to the Moon, indicating that it has not changed much over billions of years. It has a very thin atmosphere, which makes it unable to retain heat. Additionally, 수성 has a short orbital period, completing a full orbit around the Sun in just 88 Earth days.