Dynamic Textures

Northeastern portion of unnamed crater ejecta. LROC NAC M138600267R, image width is 1080 meters. Image center is 77.086°N, 200.336°E, incidence angle is 80.3°. North is up [NASA/GSFC/Arizona State University].

This far side high latitude (77°N) fresh crater (~1.1 km in diameter) presents striking linear patterns in its ejecta. Due to the high latitudes, the incidence angle is always very high in this area (including this image), which enhances subtle topographic features. The ejecta source crater is toward the bottom left (off the image), thus the ejecta landed with the velocity component in upper right direction, consistent with the linear stripes dominating whole area of this image.

LROC WAC monochrome mosaic (100 m/pix) of the unnamed crater and surrounding area. Image center is 77.46°N, 200.83°E, image width is about 142 km. NAC footprint (blue box) and the location of today's Featured Image (white arrow) are indicated here [NASA/GSFC/Arizona State University].

Interestingly, the lower left (closest to the rim) and upper left corners of this image show a craggy, rough surface, while the right portion shows only the striped pattern. What causes such texture differences within the same ejecta blanket?

One possibility is the impact melt content was enriched near the rim, increasing the cohesion among the rock fragments and decelerating the flow inducing multiple pressure ridges perpendicular to the flow direction. Perhaps variations in roughness of the pre-existing surface controlled the final look of the ejecta. What else?

Explore this fascinating ejecta morphology in full NAC frame, and find your own hypothesis and answers!

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Published by Hiroyuki Sato on 16 May 2013