Friday, May 10, 2013

Small Bouldery Crater

A small crater, sporting a healthy population of boulders and a persistent higher reflectance surrounding ejecta blanket, on the rim of Planck W crater in the farside highland terrain. LROC Narrow Angle Camera (NAC) frame M1120363462L, field of view 500 meters across, resolution 0.5 meters, LRO orbit 17306, April 11, 2013 [NASA/GSFC/Arizona State University].
Drew Enns
LROC News System

The small crater featured today is a bit atypical. The crater's ejecta blanket has a higher reflectance than its surrounding, its interior is peppered with a number of boulders, and it has a poorly developed rim. Bright ejecta normally implies a fresh crater, but with the poorly developed rim it does not appear to be 'fresh'. So it could be either a secondary crater formed from a nearby cratering event, or it could be a fresh crater with an anomalously degraded morphology.

A better idea of the local geology might help with our interpretation.

The small crater of interest (upper right) in context with the rim and wall of Planck W (lower left), and a larger and likely younger crater further up the slope (upper left), with a more reflective ejecta blanket. An approximately 2.8 km wide field of view from a mosaic of the right and left frames of LROC NAC observation M172067030, spacecraft orbit 10491, October 1, 2011; angle of incidence 54.39° at 0.64 meters resolution from 61.39 km [NASA/GSFC/Arizona State University].
The small crater apparently sits on the rim of the larger crater Planck W. (the) ejecta blanket (of an adjacent small crater) is highly reflective - (it's) all you can see of the crater in the WAC context image!

Context for the LROC Featured Image, a high-resolution NAC view of the small crater barely visible at upper right in the field of view outlined above (shown in an earlier NAC observation, immediately preceding. The area of interest is on the slope of Planck W (55.44°S, 131.28°E). View cropped from LROC Wide Angle Camera (WAC) observation M110751697C (643 nm), orbit 1455, October 21, 2009; resolution 82.1 meters per pixel, angle of incidence 58.35° - spacecraft altitude 58.6 km [NASA/GSFC/Arizona State University].
In this case it appears that the crater is young since its ejecta blanket is still around. But then why does the crater not look morphologically fresh? It could be a form of physical mass wasting. Diffusion models of the lunar surface indicate that small craters are quickly degraded in terms of their morphology, but the ejecta blanket is not affected. Resulting craters might look very similar to today's Featured Image.

Look for more fresh craters in the full LROC NAC, HERE.

Related Posts:
Symmetric Ejecta
Beautiful Ejecta Patterns

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