As MESSENGER neared Mercury on Jan 14, 2008, the spacecraft took this image of the planet’s full crescent. The image shows portions of Mercury previously seen by Mariner 10. However, when Mariner 10 flew by the planet at each of its encounters, the sun was nearly overhead. For this MESSENGER flyby, in contrast, the sun is shining obliquely on regions near the day/night boundary (called the terminator) on the right-hand side of the crescent, revealing the surface topography.
This image illustrates how MESSENGER, during its future flybys and subsequent orbital mission, will teach scientists much about the portion of Mercury already imaged by Mariner 10.Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington