Tuesday, July 10, 2012

LROC: "Sunny Side Up"

The center of Linne F is filled with a small mound surrounded by a moat of impact melt rock. Image width is ~1450 m, LROC Narrow Angle Camera (NAC) observation M190509409, LRO orbit 13120, May 1, 2012; native resolution 1.5 meters. View the larger (1100 px)) LROC Featured Image release, HERE [NASA/GSFC/Arizona State University]
Drew Enns
LROC News System

Linne F is a 5 km diameter crater located at 32.33°N, 13.95°E, and it displays a spectacular melt pond (now frozen) on its floor. Immediately after the impact event, melt pooled and eventually hardened to form the now lower reflectance flat deposit surrounding a central mound. The once molten material shares characteristics that are seen in many other impact craters: small mounds, blocky craters, and fractures. But what is the origin of the central mound? Compare the central mound in Linne F to the interiors of other similarly sized craters. Perhaps it is a proto-central peak or maybe the mound formed due to unusual target properties?

Linne F, surrounded by Mare Serenitatis basalts. LROC QuickMap (64 meters resolution) with profile statistics; field of view is 37.12 km [NASA/GSFC/Arizona State University].
Do any other 5 km diameter lunar craters have central peaks? On the Moon, central peaks start to form in craters between 10-20 km in diameter, much larger than Linne F. If the mound isn't a nascent central peak, perhaps the local target properties of this portion of Mare Serenitatis played a role. Target properties are important for small (<500 m diameter) craters as a loose regolith over solid bedrock can result in benches, mounds, and flat floors. It is unclear if target properties are also important for larger craters, but Mare Serenitatis has a thick layer of basalt overlying older basin material. Both hypotheses are possible, but hard to prove from remotely sensed data alone. Linne F is just one example of the uniqueness of each crater on the Moon. It is easy to generalize that all craters below 10 km in diameter are bowl shaped - but that generalization glosses over the variety of geologic forms seen in lunar craters. It is this richness of detail from crater-to-crater that scientists are studying to unravel the story of the surface, and subsurface, of our nearest neighbor!

Explore more impact melt in the full LROC NAC mosaic, HERE.

Related Posts:
Cracked Mound
Shattering Consequences
Farside impact!

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