|Dry debris flows terminate on the cracked and bouldery melt sheet in Mare Tranquillitatis landmark crater Moltke, 43 kilometers southeast of the landing site of Apollo 11. A textural change marks the boundary between crater wall and impact melt deposits embaying the crater floor. Image field of view 1100 meters. Credited as LROC Narrow Angle Camera (NAC) observation M122591558L, orbit 3200, March 7, 2010; resolution 0.5 meters from 40.63 km. View the full size LROC Featured Image (labeled M183360570RE) HERE [NASA/GSFC/Arizona State University].|
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In the absence of an absolute age date, lunar scientists have to rely on the geomorphology of a crater to determine how old it is relative to other craters. The sharpness of the deposits in today's Featured Image is a good indicator that Moltke is young, probably Copernican in age. Large cracks in the impact melt formed as the melt cooled and contracted towards the center of the crater. The uneven terrain within the melt is probably composed of smaller ejecta blocks that have been mixed in with the impact melt. These features have not been covered by regolith or debris flows from the crater wall that naturally accumulate over time, indicating that Moltke is probably young. Do these observations agree with a larger contextual view?
|Context for the LROC Featured Image (FOV yellow arrow). Moltke (0.589°S, 24.180°E) is barely 6 kilometers in diameter but has a diffuse high-reflectance ejecta blanket that makes it very easy to spot in modest telescopes trained in on the south-southeastern corner of Mare Tranquillitatis, nestled between the craggy "horns" of the contact separating the relatively flat Sea of Tranquility. This makes it easy to spot, at least in the mind's eye, the spot where "man first walked upon the Moon, July 20, 1969, a very little distance to the northwest. LROC Wide Angle Camera (WAC) observation M144463675CE, orbit 6463m November 15, 2010; resolution 62 meters from 45.07 kilometers [NASA/GSFC/Arizona State University].|
These observations do agree with the larger contextual view! A bright halo of ejecta surrounds Moltke, superposing older and darker mare material. The "freshness" of the impact melt and crater wall, the brightness of the ejecta blanket all argue that Moltke must be a relatively young Copernican aged crater.
|Sparely labeled HDTV frame of the southwestern corner of Mare Tranquillitatis, landing site of Ranger 8, Surveyor 5 and Apollo 11, as captured by Japan's lunar orbiter SELENE-1 (Kaguya) and released November 2009. View an enlarged version HERE [JAXA/NHK/SELENE].|
Explore more of the Moltke melt sheet in the full NAC frame!
The dry debris flows in the context of the western side of Moltke crater were also imaged from LRO during the brief and extraordinary low-periapsis maneuvers, on August 15, 2011, from only 24.96 kilometers altitude; with resolution of 40 centimeters. Those unique unprocessed frames are M168048451L and M168048451R.
Melt and more melt