A Terminator Shot
October 2, 2009
As MESSENGER approached Mercury, the NAC acquired a high-resolution mosaic of the sunlit crescent planet that contained 62 images. To ensure that the entire sunlit portion of Mercury was covered in the mosaic, a few of the images, like the one here, have large areas of blackness. The terminator, the division between the dark night side and light dayside, runs through the middle of this NAC shot. Shadows are elongated in this image, as the craters catch the rays of an evening Sun. At the actual terminator location in this image, only the highest points of crater rims and inner peak rings are seen illuminated by sunlight. Such grazing lighting conditions can provide important information about the heights of geologic features on the surface.