Tuesday, June 5, 2012

LROC: Melt Boundary

Impact melt boundary at a wall slump in Milne N crater. Melt on the right, slump on left; LROC Narrow Angle Camera (NAC) observation M169840154R, LRO orbit 10163, September 5, 2011; field of view 500 meters across, angle of incidence 39.44° with a resolution in the larger LROC Featured Image 0.52 meters per pixel, from  49.02 kilometers [NASA/GSFC/Arizona State University].
Lillian Ostrach
LROC News System

Craters on the Moon come in all shapes and sizes. Many factors, including impact velocity, target material, projectile material, and angle of impact, influence the final crater morphology and the generation of impact melt, which is why no two craters are exactly the same. Milne N crater (35.828°S, 111.275°E, ~40 km diameter) exhibits substantial crater wall slumping and an irregular crater rim in addition to impact melt ponds on the crater floor. The slumped portions of crater wall modified the crater interior while the impact melt was still at least partially molten. As a result, the crater floor is not as flat as other craters with impact melt deposits, and a contact between impact melt and slumped wall material is observed in the opening image.

One meter resolution step down shows the field of view in the LROC Featured Image released June 5, 2012 shows the impact melt contact in context with the slumped walls of crater Milne N. The LROC Wide Angle Camera (WAC) context image below includes, also from the LROC QuickMap, includes an inset showing the elevation differences lost to single NAC frames [NASA/GSFC/Arizona State University\.

LROC WAC monochrome mosaic centered on Milne N, satellite crater of Milne. The asterisk notes location of the field of view highlighted in the LROC Featured Image. View the wider area surroundings in the uncropped context image accompanying the LROC news release HERE [NASA/GSFC/Arizona State University].
Looking at the opening image, the contact between slumped crater wall and melt is emphasized by the presence of perched boulders on the wall, some of which have rolled down the slope to the edge of the melt pond. Note the presence of superposed impact craters, fresh and degraded, on the impact melt. The numerous small superposed craters indicate that although Milne N is youthful in age to many surrounding craters, compared to other craters with impact melt (such as such as Jackson crater, Rümker E crater, Thales crater), it is relatively older. The soft-looking surface of the melt in Milne N suggests that enough geologic time has passed for the melt to develop a thin regolith layer, thus eroding the crisp-looking surface of melt to a smoother texture.

Can you trace the melt pond boundaries in the full LROC NAC image, HERE?

Related Posts:
Impact Melt Boundary
Fractures in Ohm's Melt
On the Floor of Thales

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