Making a Mosaic
During MESSENGER's flyby of Mercury on January 14, 2008, the Mercury Dual Imaging System (MDIS) acquired images to create eight different mosaics. Shown here is an image context sheet with small thumbnail versions of the MDIS Narrow Angle Camera (NAC) images that were captured as the spacecraft approached the planet and used to create a high-resolution mosaic of Mercury. The MDIS instrument is mounted on a pivot, which enables the camera to point in different directions and see different portions of the surface. Both small motions of the spacecraft and movement of the pivot were used to take the images that compose this mosaic sequence. This mosaic has images in 5 columns by 11 rows, but images of just black space or of the unlit, dark planet are not shown on this context sheet.
MDIS started this mosaic 55 minutes before MESSENGER's closest pass by Mercury. The first image of the mosaic was taken in the lower left corner, and images were subsequently acquired by moving across a row and then up to start the next row. An image where Mercury's surface fills the image is about 500 kilometers (310 miles) across. Image names, which are abbreviated under each image in this context sheet, are derived from the mission elapsed time (MET) when the image was taken, which is approximately the time in seconds since launch. The mosaic was planned to have about 10% overlap between neighboring images, to ensure that a mosaic could be formed without any gaps. The resulting mosaic is ultimately created by using the time of each image and corresponding information about the spacecraft location and viewing geometry at that time to place all of the images onto a common map of Mercury.