Thursday, May 9, 2013

Messy Crater in Mare Australe

Fresh impact crater morphology can be messy! Deep interior of relatively small, unnamed fresh impact crater in Mare Australe. 708 meter wide field of view cropped from LROC Narrow Angle Camera (NAC) mosaic M189978900LR, LRO orbit 13045, April 25, 2012; resolution 60 cm per pixel, angle of incidence 57.76° from 58 km [NASA/GSFC/Arizona State University].
Lillian Ostrach
LROC News System

Cartoons illustrating the three stages of impact cratering (contact/compression, excavation, and post-impact modification) usually show the formation of a beautiful, bowl-shaped simple crater.

LROC NAC images reveal that while there are many bowl-shaped craters, there are also many craters that are not bowl-shaped or even very circular.

Today's Featured Image is an approximately 1 kilometer in diameter crater (45.661°S, 93.016°E) with a very irregular interior morphology. This crater exhibits a defined rim for all but a small portion of the crater (shown in the opening image). In this region, the crater wall is a jumbled mass of material that looks more similar to wall collapse than crater cavity excavation. The surrounding crater walls are covered with jagged blocks and impact melt veneer, and a 100 m wide melt pond with polygonal fracturing is located on the crater floor.

Near same width view of the 7.8 km wide LROC NAC mosaic M189978900LR [NASA/GSFC/Arizona State University].
Irregular crater morphology can be attributed to several factors. The impact process involves vast amounts of kinetic energy that may not be uniformly distributed throughout the target during impact. For example, a non-uniform energy distribution may be the result of an oblique impact, a steeply sloped target surface, or perhaps a low velocity secondary impact. Similarly, target properties, such as re-existing weakness or strength variations in the target rocks, may influence crater shape. Because the impact process is complex, it is often difficult to determine which factors dominate when studying craters with irregular morphologies. However, for today's crater, it is likely that some of the crater morphology irregularity is associated with the target slope; the impact occurred on the outer wall/rim slope of a degraded crater.

LROC Wide Angle Camera monochrome mosaic centered on the recent impact highlighted in the opening image [NASA/GSFC/Arizona State University].
Take a look at the full LROC NAC image, HERE, and explore the morphology of the young crater for yourself.

Related Posts:
Ejecta Starburst
Farside impact!

Hemispheric view over the southern east limb of the Moon, centered on the location of the small impact crater on the 93rd meridian east. LROC WAC 100 meter Global Mosaic, LROC PDS image search tool [NASA/GSFC/Arizona State University].

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