Chappy crater
NW wall of spectacular young impact crater perched on the rim of Chaplygin crater. The dark smooth material (bottom right) is solidified impact melt that originally pooled on the crater floor; the dark, middle and bright tones on the slope wall indicate various proportions of impact melt rock mixed with local regolith (soil). Image width ~700 meters, M1194434063LR, 4.079°S, 151.682°E [NASA/GSFC/Arizona State University].

Zowie! How can such an incredibly violent event result in such a delicate composition? Asteroids and comets (generically known as bolides) slam into the surface of the Moon at speeds typically greater than 15 kilometers per second (10x faster than a speeding bullet). So much energy is released that much of the bolide is vaporized and target rock is excavated and ejected at a range of speeds. Very young craters such as the one shown here provide the key to understanding the physics of these powerful events. The delicate patterns show stages of ejection, mode of travel, thickness of deposited materials and the effects pre-existing topography on ejecta flow.

Chappy Shrunk 19x Full Width
Full LROC view of Chappy crater (1400 m diameter) shrunk by a factor of 19x. Chappy's ejecta spreads out more than ten diameters from the crater, much further than previously thought.

Chappy is a temporary name given to this beautiful crater, a diminutive form of Chaplygin crater upon which Chappy formed. Perhaps some day the International Astronomical Union will give Chappy an official name.

3x Reduced Detail of Chappy Ejecta
Close-up of ejecta on the western side of Chappy crater. Note the sharp terminations of flows, and the way that flows are diverted around small obstructions. The latter form shows that significant portions of ejecta traveled as a ground hugging flow, rather than on a ballistic trajectory.

There are many amazing features to be explored in the whole full-resolution NAC mosaic (M1194434063LR, 4.079°S, 151.682°E):

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Published by Mark Robinson on 1 March 2016