The smallest planet in our solar system is Mercury. It orbits closest to the Sun, making it the innermost planet. Mercury has an average diameter of about 4,880 kilometers (3,032 miles) and has a rocky surface marked by craters. Despite its small size and proximity to the Sun, Mercury experiences extreme temperature fluctuations, ranging from blazing heat during the day to freezing cold at night. Its unique characteristics and position make it a fascinating subject of study in planetary science.