Mosaic of four Mariner 10 images showing the eastern Caloris Basin on Mercury.  The images were taken within approximately 2 minutes of each other on Mariner 10's first flyby (of three).  The rest of the Caloris Basin is in shadow to the left, and was not imaged until the MESSENGER spacecraft flew by Mercury in 2008.
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=192">192</a>, <a rel="nofollow" class="external text" href="http://ser.sese.asu.edu/M10/IMAGE_ARCHIVE/SingleImage.html?image_number=193">193</a>, <a rel="nofollow" class="external text" href="http://ser.sese.asu.edu/M10/IMAGE_ARCHIVE/SingleImage.html?image_number=194">194</a>, <a rel="nofollow" class="external text" href="http://ser.sese.asu.edu/M10/IMAGE_ARCHIVE/SingleImage.html?image_number=195">195</a>