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Chaotic Crater Floor in Tycho
The floor of Tycho crater is covered in many places by a chaotic surface of impact melt forms. Image scale is 0.5 m/pixel, image width is 500m. Incidence angle 84°, sunlight is from left side [NASA/GSFC/Arizona State University].
The bottom of Tycho's crater is covered by blocks, boulders and impact melt textures. The impact melt deposits often show networks of fractures visible at the LROC WAC pixel scale of 100 meters. At NAC resolution with very high incidence angles (illuminated almost along the horizon), the extremely complicated and chaotic nature of the surface is striking.
Impact melts have extremely complicated thermal histories. When the impacting meteoroid's kinetic energy is large enough, the initial temperature of an impact melt can be much higher than that of normal magma, which is driven by volcanic activity. The melts are mixed together with ejecta debris, flow down slopes and puddle; loosing heat and increasing in viscosity with time. Once settled in the crater floor, solidification starts at the top and the bottom (chilled margins), and continues little by little to the melt volume interior. Any kind of deformation during this time (for example, the isostatic rebound of the crater floor, uneven thermal contraction, or late flows pushing pre-existing melts) will disturb the solidifying melt surfaces to make the chaotic patterns and sometimes cause local "eruptions" of melt onto the newly solid layer.
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LROC WAC 100 m/pixel mosaic of Tycho impact crater cavity, overlayed by WAC color DTM 500 m/pixel (DLR, Germany). Image center is about latitude 43.32°S, longitude 11.25°W. Blue box and yellow star indicate the locations of NAC frame and today's Featured Image [NASA/GSFC/Arizona State University].
The topographic color was produced as a by-product of stereo analysis of the WAC global dataset. Producing the global Digital Elevation Model (DEM) is a big job being led by LROC team members at the German Aerospace Center (DLR; English version) in Berlin.
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