Lunar Reconnaissance Orbiter Camera

Off-centered deposits

Impact crater exhibiting boulders clustered off center, the crater also has a poorly defined rim. What could be the cause of these distinctive features? LROC NAC M1117124706L, image width is 900 m [NASA/GSFC/Arizona State University].

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.

Context image of today's Featured Image (red asterisk) located inside Guthnick crater at -48.270°N, 266.157°E. Image width is 100 km [NASA/GSFC/Arizona State University].

Asymmetric craters tend to form when the impact angle is <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. The slope of the Guthnick crater's wall had a big effect on the morphology of this simple crater. During the impact event the steep slope resulted in collapse of the downhill portion of the crater, thus the asymmetric shape and collection of boulders on the downhill side.

Explore more of Guthnick crater's interior in the full LROC NAC!

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