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Mounds in a Melt Pond
Bottom of Laplace A crater cavity › View larger image
Bottom of Laplace A crater cavity. LROC NAC M129466485R, 0.80 m/pixel, image width is about 960 m. Sunlight is from lower-right side, incidence angle is 66° [NASA/GSFC/Arizona State University].

During an impact event the kinetic energy of the meteorite is dissipated by compression, fragmentation, excavation and launching rock debris -- all resulting in an impact crater. The large amount of energy released also melts some of the target rock, and often times impact melt ponds form in the floor of the crater. Since the impact melt is liquid, it seeks an equi-potential level (surface is perpendicular to the gravity vector), thus it is flat and smooth as it freezes.

Today's Featured Image reveals the bottom of Laplace A crater, specifically the north edge of its impact melt pond. The upper side of this image corresponds to the lower part of crater wall, covered by lots of boulders. The surface of this melt pond consists of dozens of low mounds, possibly due to deformation of the pond surface after partial solidification. Perhaps rebound of the crater floor caused the level of molten material beneath the crust to rise and create small breakouts to the surface. There is also a cone shaped depression near these mounds. It may have formed as magma drained out from below?

Context map around Laplace A crater › View larger image
Context map around Laplace A crater. Image center location is 42.57°N, -29.73°E. LROC WAC 100 m/pix mono-chrome global mosaic overlayed by WAC color DTM 500 m/px. Blue long box at the image center corresponds to the footprint of today's featured NAC image [NASA/GSFC/Arizona State University].

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