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MESSENGER's enhanced coverage of Mercury's surface

MESSENGER's enhanced coverage of Mercury's surface
MESSENGER's enhanced coverage of Mercury's surface Three maps tell the story of progress in the mapping of Mercury by spacecraft. To date, all spacecraft visits of Mercury have been flybys. For each flyby, only half of the surface was illuminated, a portion of which was visible as the spacecraft was flying toward the planet ("inbound") and a portion as the spacecraft flew away from the planet ("outbound"). Mapping began with three flybys by Mariner 10 in 1974 and 1975, during which the same portion of Mercury was always illuminated, from about 350 to 170 degrees east longitude; of that, a small area in the northern hemisphere was always beyond the limb of the planet during each flyby, producing the gore in the upper mosaic. The next spacecraft to fly by Mercury was MESSENGER, in January and October of 2008. The two MESSENGER flybys occurred about 1.5 Mercury solar days apart, so complementary portions of the planet were illuminated by the Sun. During these two flybys, MESSENGER mapped a total of 80 percent of the planet. Combined with the previous Mariner 10 coverage, about 90 percent of Mercury has now been mapped by spacecraft. NASA / JHUAPL / CIW