|A small 600 meter crater inside the rim of Guthnick, a Copernican impact integral to the Mendlel-Rydberg basin immediately south of Mare Orientalis. This small impact crater exhibits boulders clustered off center, along with a poorly defined rim. Drew Enns asks, "what could be the cause of these distinctive features?" - Crop from LROC Narrow Angle Camera (NAC) M1117124706L, spacecraft orbit 16850, March 5, 2013; 0.60 meters per pixel resolution, above field of view 3 km [NASA/GSFC/Arizona State University].
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Small impact craters are normally bowl-shaped depressions in a planetary surface. Because of this, boulders and impact melt will also fill in the center of the crater. Yet this is not what we observe in today's Featured Image. Why does this small crater have boulders that are off center? Why is the northern portion of the rim undefined? Is it some sort of dynamical fluke? Probably not. It is more likely that there is some uneven terrain influencing the crater. We can zoom out for a larger view.
Asymmetric craters tend to form when the impact angle is greater than 15° The LROC WAC context mosaic helps a lot! We now see that our small crater formed on the wall of the much larger Guthnick crater.
|LROC Wide Angle Camera (WAC) context for the small crater (arrow) on the wall of Guthnick crater at 48.27°S, 266.157°E. Though Guthnick is not the subject of this post, the 36 km crater has been identified as one of two that satisfy requirements for sampling intact basin melt sheets. (Science Concept 2: "The structure and composition of the lunar interior provide fundamental information on the evolution of a differentiated planetary body;" CLSE, 2012, pg 115) - LROC WAC observation M112231731CE (604nm), spacecraft orbit 1673, November 7, 2009; resolution 74.25 meters per pixel from 52.51 km [NASA/GSFC/Arizona State University].
A Tiny Glancing Blow
Not Your Average Crater
|Figure 2.43 (A Global Lunar Landing Site Study to Provide the Scientific Context for Exploration of the Moon, 2012) Topographic profile of Guthnick. Black arrows indicate the transition from upper crater wall to slumped material, as shown by an inflection in the slope. The map uses a polar projection centered on 48°N, 266°E, and the vertical projection of the elevation profile is about 2:1 [CLSE/NLSI/LPI].