Planet Profile: Mercury
1. Basic Facts
Mercury is the closest planet to the Sun and the smallest planet in the Solar System. It has a diameter of 4,880 km (3,032 miles), which is only slightly larger than Earth’s Moon. Because of its proximity to the Sun, Mercury experiences extreme solar radiation and has a rapid orbital speed. Despite being the closest planet to our star, it is not the hottest—Venus holds that title due to its thick atmosphere. Mercury has no moons or rings, and its surface is covered in craters from constant asteroid impacts. Scientists believe Mercury’s composition is unique, with a very large metallic core making up the majority of its mass. Although ancient civilizations observed Mercury for centuries, its secrets remained largely unknown until the space age, when spacecraft like Mariner 10 and MESSENGER provided detailed images and data about this mysterious world.