This image of Mercury was take about 55 minutes before closest approach as the MESSENGER spacecraft sped toward a crescent-lit planet during the mission's second flyby. The large crater in the center of the image is near the terminator, the division between the dayside and nightside of the planet. The low angle of the Sun near the terminator causes the long shadows seen here, which reveal that a large scarp or cliff bisects the crater. The crater exhibits a smooth floor broken by slight ridges and seems to have been filled with volcanic lava flows. In the lower left of the crater, the outline of a smaller crater that was filled to its rim by lavas is still visible. The scarp was formed after the large impact crater was filled with the lava flows, for if the scarp had formed first, then the lavas would have flowed over the scarp and buried it.