Thursday, June 12, 2014

Study in superpositioning at Vavilov D

Sunrise, sunset. LROC NAC observations 10 months apart, one at local sunset and the other after local sunrise, both from nearly identical altitudes and resolutions, capture these views of double "dingleberries," drops of hot melt, very likely from the impact that created Vavilov crater, sit where they quickly flattened and cooled, just inside the steep slope of ancient Vavilov D. The Vavilov craters are a study in stratigraphy and superposition [NASA/GSFC/Arizona State University].
Immediately inside the northwest rim of highly degraded Vavilov D, twin disks of impact melt, likely from the formation of Vavilov, came to a standstill at the upper end of a contiguous slope of 5000 meters elevation, over about 40 km, into the complex floor of the latter Eratosthenian crater. This 1400 meter field of view (down slope is to the lower right, centered on 1.14°N, 221.536°E) from LROC NAC observation M1128031686L, LRO orbit 18385, July 9, 2013; 61° incidence angle, resolution 1.17 meters from 114.6 km [NASA/GSFC/Arizona State University]. 
Hiroyuki Sato
LROC News System

Vavilov D is an heavily degraded crater (96.1 km; 0.026°N, 220.93°E) sits between the Orientale basin and Jackson crater, both of which it may pre-date.

The later formation of the nearly identical, over-lapping Vavilov crater (98.2 km; 0.87°S, 221.23°E) eradicated the entire southwestern half of Vavilov D.

The second image above spotlights a spot on the northwestern curve of the wall of Vavilov D near where the Eratosthenian Vavilov erased the older crater's anatomy. The relatively smooth textured area in the upper left corresponds to the outside of Vavilov D, and the rest of rough/craggy surface is the interior crater wall's steep slope. 

The two degraded craters (~280 m in diameter) near the middle of the opening image exhibit fascinating overlying smooth features that may have formed as material flowed downslope (arrows).

View the full-resolution original HERE. The twin melt disks are located where the rim of Vavilov superseded that of Vavilov D, in the farside equatorial highlands,  where Vavilov is etched into terrain 8000 meters above the global mean elevation. It's possible an astronaut could walk from this location south into the interior of Vavilov. 5.6 km-wide field of view from LROC NAC observation M1128031686L [NASA/GSFC/Arizona State University].
Other morphologic pits/dents on this slope also have similar textures. What we are seeing here are most likely remnant impact melt that was thrown out of the Vavilov crater. Craggy sloped surfaces with patches of smooth material are often found associated with young impact craters -- formed as impact melt flowed over and around the newly formed crater.

The deepest material brought to the surface by impacts on the Moon is found on the resulting crater's rim. A fresh crater near our area of interest, on the rim of Vavilov D (cross), exposes material excavated by that ancient impact, and Vavilov D, in turn, is nested on the Hertzsprung basin. The larger region is also at the outside range of the majority of secondary craters from the Orientale basin-forming impact. LROC Quickmap mosaic [NASA/GSFC/Arizona State University].
Depth of field in lunar photography is a fleeting quality. With the LROC WAC-derived elevation model (GLD100), however, the super-positioning of Vavilov D (and an aeon or two later, Vavilov) on Hertzsprung is much easier to detect, along with some of the most extreme elevation ranges, some 9 km above the global mean [NASA/GSFC/DLR/Arizona State University].
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