August 29, 2006

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Deep Down and Impossible to See

Orlov & LeeuwenhoekAS17-150-22948.jpg
image from Apollo 17 Astronauts

The lunar farside is another world, one that most of us know little about. If only the Moon were not in locked rotation. If only it swung around its axis a little slower or a little faster so we could see it all. This is one view we are missing. It is the farside highlands, but they are not as old as the highlands near Tycho, for everything here lies on the floor of the South Pole-Aitken Basin at about 180° longitude and 30°S latitude. When that basin formed is unknown (probably before 4.0 b.y.) but it destroyed all the landforms that had previously been there - all of this roughness formed by subsequent impacting. The smooth mare material in the 125 km wide Leeuwenhoek is a clue that we are within the SPA Basin for that is where the majority of farside mare is found. Another mare exposure is just visble in the crater Leibnitz near the southern horizon. And although you can’t tell by looking, the floors of Leeuwenhoek and Orlov (center-left) are about 4 km below the average lunar radius. This is the lowered floor of the giant SPA Basin, but its lowest spots, 5 km deeper, are about 1500 km south - it is a huge hole!

Chuck Wood

Technical Details:
Hasselblad + 80 mm focal length lens. Apollo 17-150-22948. Image cropped and enhanced by Stefan Lammel.

Related Links:
Clementine Atlas plate 104

Yesterday's LPOD: To the Moon and Beyond

Tomorrow's LPOD: A Classic Trio


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