Thursday, October 11, 2012

Hole on A Melt Sheet

A portion of the impact melt sheet on the floor of crater Korolev X. Image centered on 0.699°N, 200.594°E, field of view is 638 meters, illumination from the right, or east. From LROC Narrow Angle Camera (NAC) observation M145664820R, LRO orbit 6600, November 29, 2010; angle of incidence 61.4° at 0.64 meters resolution, from 61.62 kilometers  [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

Korolev X is a 25-km crater located at 0.54°N, 200.59°E. As seen in the bottom image, the northern rim of this crater was destroyed by a younger crater about 16 km in diameter. The heat from the impact that formed this younger crater melted a large volume of rock, which flowed down onto the floor of Korolev X, creating a sheet of solidified melt 14 x 5 km across. The opening image highlights a dent in the surface of this melt sheet.

This dent is about 105 meters in diameter. Considering the existence of multiple, similarly-sized (around 100 m in diameter) craters on this melt sheet, this dent is most likely an impact crater even though neither an ejecta blanket nor a raised rim can be clearly recognized. Along the top of the crater wall there appears to be a thin layer of the melt sheet that is exposed and highlighted by the angle of the sun. Below this surface layer no clear layering is observed, implying a rather homogeneous structure. Small craters like this are often observed in impact melt sheets, and why they lack typical features of impact craters (a well-defined raised rim, a thick ejecta blanket) is still not well known. Could these craters have formed when the impact melt was still partially molten?

Korolev X and surroundings from an LROC WAC monochrome mosaic (100 m/pixel) centered near 0.52°N, 200.57°E. The blue box indicates the footprint of LROC NAC observation M145664820R with their Featured Image field of view designated by the yellow arrow [NASA/GSFC/Arizona State University].

Explore various strangely shaped craters on this melt sheet in full NAC frame yourself, HERE.

Related Posts:
Necho Crater
Scalelike Impact Melts
Impacts on the Melts
Impact Melt Deposits On A Crater Rim

More detail, at small scale, shows the elevation range north and south of Korolev X, near the rim of mighty Korolev basin. Less than 200 km to the north of the area of interest is the Moon's highest elevation. Though all of Korolev range as high as 10.2 km lower than the east rim of Engel'gardt (and unlike the familiar nearside basins), nowhere in Korolev falls below the Moon's global mean. The farside of the Moon is very different than the nearside [NASA/GSFC/Arizona State University/DLR].

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