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Nature 418, 27-28 (4 July 2002) | doi:10.1038/418027a
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Planetary science: An older face for Mars
Sean C. Solomon
Abstract
Mars has a north–south divide in the age of its surface, as judged by the density of impact craters. Altimetry data, which by inference provide a subsurface view of the planet, reveal that the divide is only skin deep.
A surprising finding from the exploration of Mars by orbiting spacecraft in the 1970s was that the southern and northern hemispheres have very different surfaces. The density of impact craters seen in images taken by Mariner 9 and Viking Orbiter indicated that the surface of the topographically high southern hemisphere is old enough to have preserved the effects of the early, heavy impact bombardment of the inner Solar System (known from lunar studies to have occurred before about 3.
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