The above is a mosaic of half of the spectacular Caloris Basin on Mercury, photographed by NASA's Mariner 10 spacecraft in 1974-75. The other half has never been photographed. The Caloris Basin is one of the largest impact basins in the solar system. Its diameter exceeds 1,300 kilometers and is in many ways similar to the great Imbrium Basin on the Moon (diameter over 1,100 kilometers).
Image Credit: Mark Robinson, Northwestern University
Credit: Lunar and Planetary Institute