Chappy Oblique

Oblique View of Chappy Crater
Spectacular oblique view (65° slew angle) of a 1400 m diameter crater that formed on the rim of Chaplygin crater. Delicate lacy fingers of ejecta highlight the hummocky and steep topography around this young crater. The very brightest material was excavated from the lower reaches of the crater and was some of the last material to exit the rapidly forming crater, M1196739735LR, 4.079°S, 151.682°E, [NASA/GSFC/Arizona State University].

Looking east to west across the rim and down into Chaplygin crater reveals this beautiful example of a fresh young crater and its perfectly preserved ejecta blanket. The delicate patterns of flow across, over, and down local topography clearly show that ejecta traveled as a ground hugging flow for great distances, rather than simply being tossed out on a ballistic trajectory. Very near the rim lies a dark, lacy, discontinuous crust of now frozen impact melt. Clearly this dark material is on top of the bright material so it was the very last material ejected from the crater.

Chappy Closeup
Close up of "Chappy" crater, on the far side of the crater you can see a thin dark piece of the frozen impact melt has cracked off the main deposit and is just about to slide down into the crater (1400 m across), M1196739735LR, 4.079°S, 151.682°E, [NASA/GSFC/Arizona State University].

The melt was formed as the tremendous energy of impact was converted to heat and the lunar crust was melted at the impact point. As the crater rebounded and material sloughed down the walls of the deforming crater the melt was splashed out over the rim and froze. Its low reflectance is mostly due to a high percentage of glass because the melt cooled so quickly that minerals did not have time to crystallize. The fact that the delicate splash patterns are so well preserved testifies to the very young age of this crater. But how young?

For comparison "Chappy" (informal name) is 200 m larger than Meteor crater (1200 m diameter) in Arizona, which is about 50,000 years old. Craters of this size form every 100,000 years or so on the Moon and the Earth. Since there are very few superposed craters on Chappy, and its ejecta is so perfectly preserved it may be much younger than Meteor crater. However, we can't know the true true absolute age of "Chappy" until we can obtain a sample of its impact melt for radiometric age dating.

Investigate all of Chappy's ejecta, at full resolution.

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Published by Mark Robinson on 18 March 2016