October 24, 2009

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Das Mystery

Lunar Orbiter (left) and Clementine (right) images from USGS Map-A-Planet

The normal - such as the perfect little bowl-shaped crater (at bottom left of the right image), and Das, the 38 km wide complex crater at upper right - offer little in the way of mystery. But fortunately, the Moon also has plenty of weird craters, such as the elliptical feature between the two normal ones. Mariotte, named for the discoverer of the eye's blind spot, is decidedly elliptical, being about 50 x 70 km across. Elongated craters may result from very oblique impacts or overlapping of two separate impacts. It is difficult to understand this odd crater. The LO image shows that the northern 2/3 is full of unstructured debris, beneath steep and sheer cliffs. The southern bit is smooth, but not dark enough in the Clementine view to appear to be mare basalt. But Mariotte does seem to be younger than the Orientale impact basin (notice the two lines of basin secondaries to the right that don't continue over Mariotte) so it is unlikely the smooth material is basin ejecta. Another oddity is the deposit of material on the eastern edge of Mariotte P, the odd-shaped crater in the 7-o'clock position. This is cut by what looks more like fractures than rilles. Without much evidence I hazard a guess that Mariotte was a near simultaneous double impact, but have no idea why there is a chaotic jumbled part and a smooth part of the floor. And did the fractured material in P simply slide down that crater's wall, or is it somehow related to its odd neighbor?

Chuck Wood

Related Links
The Clementine Atlas map 106
A higher resolution, UV-VIS Clementine view.
Zond 8 view (pointed out by Danny Caes)

Yesterday's LPOD: Trail of Skylights

Tomorrow's LPOD: Red Arrowhead


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