December 22, 2012

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Big Rims

LRO topographic images from QuickMap

When looking at the GRAIL crustal thickness map of part of the farside I was struck by how sharply defined the boundary of the South Pole-Aitken basin appears for the short segment of its rim south of the Korolev Basin. The boundary is also visible in the topography of that area (top image), but turning off the colored topo layer reveals that the scarp is not readily noticed. Measurements with the Path tool reveal that the topography rises two kilometers approaching the rim from the north, and then drops 7 km inside the basin. The mountainous inner ring - beautifully shown in an Apollo image I can't find - rises 7 km, being as high as the basin rim. Comparison at the same scale with the Orientale Basin rim (below) is instructive. Zooming in on the LRO image of Orientale's north rim shows sharp-edged mountains - cut by faulting that lowered the basin interior. Presumably SP-A's rim was equally sharp when formed but has been severely eroded. None of the inner peak rings of Orientale are as high as the the tall parts of the basin's rim, showing that the SP-A inner ring segment is unusually tall - it is also nearer the basin's main rim than are the inner rings in Orientale. Although there have been a few studies of the dimensions of SP-A and the possibility that it is of oblique impact origin, there is a real need to carefully map it.

Chuck Wood
Note: The world did not end yesterday.

Related Links
21st Century Atlas charts B8 & B10.

Yesterday's LPOD: Not the End of the World

Tomorrow's LPOD: Blue Moon


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