Mercury is the smallest planet in the solar system, and it is only slightly larger than Earth's moon. The closest planet to the sun, Mercury takes just 88 Earth days to complete a single orbit.
Mercury is a small, rocky planet with no moons or rings. Due to its proximity to the sun, surface temperatures on Mercury can reach up to 840 degrees Fahrenheit. Mercury does not possess a true atmosphere, but it has an exosphere made up of atoms that have been blasted from the planet's surface by solar radiation. This exosphere is too thin to retain heat, so temperatures can fall to -275 Fahrenheit at night, resulting in the largest swing in surface temperature of any planet in the solar system.
Mercury possesses a metallic core and an active magnetic field, although this field is only 1 percent as strong as Earth's magnetic field. An asteroid roughly 60 miles wide struck the planet some 4 billion years ago creating the Caloris Basin, an impact crater larger than the state of Texas. In 2012 water ice was discovered by NASA's Messenger probe. This ice is located in Mercury's craters around its north pole, a region thought to be permanently protected from the heat of the sun.