Thursday, January 31, 2013

Messy melt in the Lodygin crater group

Unlike some melt ponds, this melt pond does not look very smooth! LROC Narrow Angle Camera (NAC) observation M182116507LR, spacecraft orbit 11945, January 25, 2012; field of view 910 meters at 0.96 meters resolution (incidence angle 57.43°) from 94.9 km [NASA/GSFC/Arizona State University].
Lillian Ostrach
LROC News System

Impact melt forms during crater formation when part of the impact-generated shock wave energy released during the impact event is released as heat. As the shock wave passes through the target, the amount of melting is related to the shock pressures reached during impact (for more information, see Chapter 6 in Traces of Catastrophe, by Bevan French). 

Often, impact melt appears visually smooth in LROC images, particularly at the WAC scale and in large craters like Tycho. However, Narrow Angle Camera (NAC) observations like today's Featured Image show that impact melt does not always have a flat "ponded" surface. In this case, the melt ponds inside an ~5 km diameter crater (17.121°S, 215.646°E) are far from smooth. 

Why might this be the case?

Full 9.9 km-wide mosaic of both left and right frames of LROC NAC observation M182116507 [NASA/GSFC/Arizona State University].
LROC WAC monochrome mosaic of the unnamed crater in the midst of the Lodygin crater group, in the farside highlands terrain north of the Apollo basin. (Asterisk notes location of the field of view shown at high-resolution in the LROC Featured Image released January 31, 2013 [NASA/GSFC/Arizona State University].
Sometimes impact melt appears visually smooth because there is enough melt that pools to cover up the fragmented floor of the crater or wall terrace. When there is less melt, the melt may pool in localized depressions to create smoothed surfaces as well as cover the surrounding fragmented, jumbled rocks pulverized during impact. Another possibility is that as the melt formed and began to cool on the crater floor, fragmented material fell from the crater walls and rim into the crater cavity to become mixed and entrained within the melt, helping to form a rugged melt-covered crater floor.

Examine the full LROC NAC image, HERE, to see if you can discern material that was entrained before the melt cooled and blocks that may have fallen to the crater floor at a later date!

Related Posts:
Anaxagoras Exterior Melt
Rim on a Rim
Louville D

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