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| High-reflectance ejecta created a starburst pattern originating from an unnamed ~270 m diameter crater. LROC Narrow Angle Camera (NAC) observation M159059694R, field of view 855 meters from 56.96 kilometers; incidence angle 45.99° at 0.59 meters resolution, visible in the fill-size (1500px) Featured Image HERE [NASA/GSFC/Arizona State University]. |
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Small, Copernican-aged craters abound on the Moon and their ejecta blankets often look like miniature starbursts.
For young craters like this one, located on the farside, southwest of Tsiolkovskiy at 25.876°S, 136.081°E, the ejecta is high-reflectance because it was recently exposed by the impact process, and is thus really fresh material.
When we observe the ejecta blanket in detail, there are variations in
reflectance within the ejecta and it looks as though the ejecta swept
out from the crater in sheets. During the impact event, material is
ejected from the growing crater and is emplaced over a short period of
time. However, the emplacement is not instantaneous and the ejecta is
expelled from the growing crater at different speeds and angles
depending on where within the impact cavity it originates.
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| Taking a small step back, the resampled NAC image provides context for the remainder of the ejecta surrounding this beautiful fresh crater. In fact, this step back allows us to see the ejecta blanket is more expansive on the eastern side, perhaps because the impact angle was slightly oblique. LROC NAC M159059694R, resampled to 2m/pixel, field of view is ~2.6 km across. View the spectacular full-size context image HERE [NASA/GSFC/Arizona State University]. |
Some of the target rock is melted and is also sprayed out of the crater with the pulverized target material. The bright and dark fingers of ejecta seen in the opening image may represent granular and melt materials, respectively. Furthermore, the ejecta farthest away from the crater is thinner and less continuous than the ejecta closest to the crater. At the distal margins of the ejecta blanket, contrasts may simply be due to original mature material showing through between fingers of ejected fresh material. Over geologic time, the starburst pattern of ejecta will gradually disappear as the material matures, and eventually no ejecta blanket will be visible in the NAC images at all.
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| Because of its small size, the fresh crater in the images above is barely resolvable in the LROC WAC monochrome mosaic. The fresh crater is less than 300 meters in diameter, not 3 pixels across in the 100 m/pixel mosaic. Good thing we have the high resolution NAC image to observe the spectacular detail! Asterisk notes location of crater. See the larger context image accompanying this LROC Featured Image release HERE [NASA/GSFC/Arizona State University]. |
Within the full LROC NAC image HERE, how far can you trace the streamers of high-reflectance ejecta?
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