Mercury is the closest planet to the Sun and the smallest planet in our solar system. It has a rocky surface covered with craters, similar to the Moon, and experiences extreme temperature fluctuations due to its thin atmosphere. Mercury orbits the Sun in just 88 Earth days, making it the fastest planet in our solar system. Despite its proximity to the Sun, Mercury is not the hottest planet; that title belongs to Venus. The planet's surface temperatures can reach up to 430°C (800°F) during the day and drop to -180°C (-290°F) at night. Mercury's unique characteristics make it a fascinating subject of study in planetary science.