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Melt and More Melt
07.27.11
 
Southwestern edge of Rümker E crater floor. › View larger image
Southwestern edge of Rümker E crater floor. Image scale is 0.5 m/pixel, image width is 500m, incidence angle 43°, sunlight is from south-west [NASA/GSFC/Arizona State University].


The floor of Rümker E crater is exhibits a variety of beautifully preserved impact melt features. The platy surface, partially submerged boulders, and flows form an invitation to explorers! The edges of the floor are sharply overlayed by debris avalanches from the cavity slopes. How did the flows seen on the left form? Are they impact melt or later debris flows?

Whole view of Rümker E crater floor › View larger image
Whole view of Rümker E crater floor. Image width is about 2.5 km, image ID M122591558L. Square corresponds to today's Featured Image [NASA/GSFC/Arizona State University].


Crater shapes are changing with time little by little, by slope failures inside the cavity, isostatic rebound, and magma intrusions (depending on the crater size). Debris flows in Rümker E will continue to mask the melt-covered floor, eventually the whole area. There are lots of degraded craters on the Moon showing no interior melt deposits, but they may be there now buried waiting for future astronauts to uncover. Impact melts are especially interesting to geologists because they are clocks. The melting resets the internal radiometric clock so even a small sample provides the means to date the moment the impact occurred.

LROC WAC 100 m/pixel mosaic around Rümker E crater › View larger image
LROC WAC 100 m/pixel mosaic around Rümker E crater. Image center is latitude 39.09°N, longitude 302.79°E, blue box indicate NAC footprint [NASA/GSFC/Arizona State University].


› Full size images
http://wms.lroc.asu.edu/lroc_browse/view/M122591558L