Caloris basin, Mercury. Enhanced colour composite image of the Caloris basin on the surface of Mercury, showing lava floods (orange) and post-flooding craters that have excavated material from beneath the surface. The larger of these craters have exposed low-reflectance material (blue) from beneath the surface lavas, likely giving a glimpse of the original basin floor material. This crater is Mercury's youngest large impact basin. It measures approximately 1550km in diameter and is one of the largest impact basins in the solar system. Imaged by the Mercury Dual Imaging System (MDIS) on NASA's MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft.