Wednesday, May 22, 2013

Concentricity in Apollo Basin

Portion of an unnamed concentric crater in Apollo Basin. Sun is incident from the right to the left. LROC Narrow Angle Camera (NAC) mosaic M1122245918LR, orbit 17571, May 3, 2013; image field of view is 6.3 km [NASA/GSFC/Arizona State University].
Sarah Braden
LROC News System

The double-arch shape in the Featured Image is a portion of an unnamed concentric crater located in the northwestern extent of Apollo Basin (basin center at 35.687°S, 208.232°E).

The concentric crater has an inner ring, centered on 30.757°S, 205.931°E, a middle ring, and then the crater rim.

The crater formed within the mare basalt that fills Apollo Basin. The formation mechanism for concentric craters like this one is not entirely clear. One theory is that the target material is made of multiple stratigraphic layers with different strengths. If the difference between the strengths of the layers is great enough, the impact may form concentric rings.

Bench craters also form when target layer strengths are different.

Oblique NAC view of the unusual crater morphology in Apollo basin. LROC NAC mosaic M109753923LR, orbit 14102, July 21, 2012; camera and spacecraft slew off nadir 57.74° resolution roughly 2 meters per pixel from 76.2 km over 31°S, 200.62°E [NASA/GSFC/Arizona State University].
In the late 1960s laboratory experiments replicated the concentric shape of craters using targets with loose, granular material over stronger, more cohesive layers. The laboratory experiments use different materials and are at smaller scales than their lunar counterparts. Still, experiments like these are important for comparing what we see on the lunar surface to basic physical principles. What if an impact occurs in an area with highland material as one layer and then mare basalt as a second layer? What crater shape is produced if you introduce a regolith layer? These are the questions that lunar geologists use to design their experiments.

LROC WMS Wide Angle Camera mosaic of the concentric crater in context with north and northwestern Apollo basin, The crater of interest is 11.5 km across [NASA/GSFC/Arizona State University].
Explore the entire LROC NAC mosaic, HERE

Related Images:
Concentric Crater (Gruithuisen K)
Apollo Basin: Mare in a Sea of Highlands
Small Pond
LOLA's Apollo Basin
Biggest, deepest crater - an excavation of the hidden, ancient Moon

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