|A small fresh impact crater, among a number of others equally juvenile (yellow arrow) has saved future explorers a lot of expensive excavation work among some far older heavy-hitters in the west farside lunar highlands, just south of the equator and north of the vast 4 billion year-old South Pole-Aitken (SPA) basin. Notional oblique view courtesy of the LMMP and LROC Wide Angle Camera 100 meter Global Mosaic [NASA/GSFC/LMMP/Arizona State University].|
|LROC QuickMap NAC and WAC mosaic (reproduced from 16 meter per pixel resolution level) shows a distinctive low optical maturity characteristic of youthful craters [NASA/GSFC/Arizona State University].|
|A blanket of fresh ejecta from a relatively new crater (9.083°S, 161.337°E) on the floor of farside landmark Keeler, dotted with smaller low albedo craters. LROC Narrow Angle Camera (NAC) observation M123513537R, LRO orbit 3335, March 18, 2010; incidence angle 15.16° on a field of view 560 meters wide, resolution 56 cm per pixel from 54.87 kilometers. See the full size original LROC Featured Image HERE [NASA/GSFC/Arizona State University].|
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Impact crater ejecta is usually distributed semi-uniformly around an impact crater. Immature ejecta from a fresh crater has a higher albedo than the mature material on the surrounding surface, and so fresh craters easily stand out against the mature background.
So why do the smaller craters in today's Featured Image have a lower albedo? On the Moon this is often due to a cryptomare located underneath the bright ejecta blanket.
Taking a step back and looking at this area in the WAC context image gives us a better idea of how to interpret this scene.
|LROC Wide Angle Camera context for their Featured Image, November 23, 2011, of ejecta from a fresh impact crater located within much larger Keeler crater (8.75°S, 161.37°E). The subject crater is two pixels left of direct center of the above 50 km-wide field of view at the full 87.86 meter per pixel resolution of LROC WAC observation M134130438C (604 nm), LRO orbit 4900, July 18, 2010 [NASA/GSFC/Arizona State University].|
This fresh crater is actually located in the much larger 160 km diameter Keeler crater. Keeler crater is located in the highlands and instead of having a mare flooded floor, Keeler's floor is covered in impact melt. It is possible that the small craters are exposing buried impact melt under the immature ejecta. However, it is more likely that the small craters expose the mature regolith that is only thinly covered by the bright ejecta. The end result is a polka-dot laden ejecta blanket.
How many low albedo craters are there in the full NAC frame?
Dark Craters on a Bright Ejecta Blanket
Dark halo crater
Intricate young ejecta blanket in ancient Murchison Crater