These two MDIS images of Mercury were acquired at a distance of nearly two million miles from the Solar System's innermost planet. That is quite a contrast from just 10 days earlier, when the spacecraft passed a mere 140 miles above Mercury's surface during the mission's third Mercury flyby! Taking images of Mercury from such a large distance can still provide valuable data. The top NAC image was taken to support a passive scan of Mercury by the Mercury Laser Altimeter (MLA). A similar scan was conducted after Mercury flyby 1, and more details are provided in that link. In a passive scan, the MLA laser is turned off and the field of view of the instrument's sensors is swept back and forth across a swath of space that includes Mercury. Such a scan provides information about the pointing of MLA with respect to MDIS and other instruments. The bottom WAC image was acquired as part of a large imaging campaign to characterize how the measured brightness of Mercury's surface is controlled by changing lighting conditions; more details about this imaging campaign can be found by visiting this previously released image.

Date Acquired: October 10, 2009
Image Mission Elapsed Time (MET): 163657779, 163658285
Instrument: Narrow Angle Camera (NAC) and Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Scale: Mercury's diameter is 4880 kilometers (3030 miles)
Spacecraft Altitude: 2,900,000 kilometers (1,800,000 miles)

These images are from MESSENGER, a NASA Discovery mission to conduct the first orbital study of the innermost planet, Mercury. For information regarding the use of images, see the MESSENGER image use policy.