Mosaic of two Mariner 10 images showing Balagtas crater (right), Kenko crater (center) and most of Mahler crater (upper left) on Mercury.  The images were taken within less than 1 minute of each other on Mariner 10's first flyby (of three) on March 29, 1974.
James Stuby based on NASA images
Mariner 10 Image Archive, images <a rel="nofollow" class="external text" href="http://ser.sese.asu.edu/M10/IMAGE_ARCHIVE/SingleImage.html?image_number=27426">27426</a>, <a rel="nofollow" class="external text" href="http://ser.sese.asu.edu/M10/IMAGE_ARCHIVE/SingleImage.html?image_number=27427">27427</a>