MOLA data (right) reveal a very large number of buried impact basins on Mars not visible in image data (left). Two from the lowlands are shown above (right; blue circles), below the obvious 80 km wide crater Korolev . More than 550 buried basins exist in the lowlands of Mars.
Buried impact basins in the northern third of Mars (above) are more numerous than visible basins in the highlands. The lowlands (below the young plains) formed very early in martian history, well before the end of intense cratering (below). This suggests the highland/lowland crustal dichotomy formed in the earliest period of Mars history and not later, as previously believed.
Lowlands existed before the end of intense early cratering on Mars.
Cumulative density versus diameter curves show buried lowland basins (red) > 100 km across outnumber visible highland basins (open blue squares). Buried lowlands (below the young plains) are older than the visible (exposed) highland surface.
Contact: Herb Frey, GSFC, Code 921 (frey@core2.gsfc.nasa.gov)
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Responsible NASA official: Dr. Herbert Frey