Tuesday, October 22, 2013

Fractured melt rock on Jackson's terraced wall

Close-up on fractured impact melt  ponding high on the west wall of Jackson crater. LROC LROC Narrow Angle Camera (NAC) M182253065R, LRO orbit 11965, January 26, 2012. Image 2130 meter-wide field of view centered on 22.534°N, 195.59°E, incidence angle is 57° at 1.47 meters per pixel resolution in the original [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

The opening image highlights a fractured pond of impact melt rock inside Jackson crater (72 km diameter). This prominent farside crater is known by its prominent ray system and large amount of impact deposits. Melt pooled not only at the bottom of the crater floor, but also on terraces of the interior wall.

The fractured melt sheet in the opening image is found amongst a grouping of melt lakes on a western crater wall terrace (see WAC context image below).

Western part of Jackson crater and surrounding areas in LROC WAC monochrome mosaic (100 m/pix). The NAC footprint (blue box) and the location of opening image (yellow arrow) are indicated [NASA/GSFC/Arizona State University].
Detached fragments from the main body of melt sheet look like a jigsaw puzzle (upper smooth surfaced portion of the image). These fragments give an impression of the thin and brittle nature of solidified impact melt. Shadow lengths show these fractured pieces to be 5 to 8 meters thick. What caused the once level and smooth ponded surface to fracture? We don't know for sure, but by looking at the whole area a plausible story can be imagined. The south part of the melt lake with the fractured plates is connected to another melt lake at a lower elevation. Perhaps drainage of subsurface unsolidified melt might have dragged a crust toward the south and broken the it into many blocky pieces. Tectonic deformation of the crater wall, perhaps consisting of whole terraces deforming, also might have occurred which could deform the brittle crust of melt ponds.

Jackson crater from Kaguya
Farside Copernican age landmark crater Jackson viewed through NHK's HDTV camera aboard Japan's lunar orbiter SELENE-1 (Kaguya) in late 2007. View the 1200 pixel-wide press release image HERE [JAXA/NHK/SELENE].
Explore this mosaic of fractured melt rock and surroundings to help unravel the complex history of Jackson crater in the full NAC frame HERE.

Related Posts:
Cracked mound (February 16, 2012)
Melt Fractures in Jackson Crater (January 20, 2012)
Tycho's flash-frozen inferno (November 2, 2011)
Waves (August 10, 2011)
Polygonal fractures on Tycho ejecta deposits (June 14, 2011)
Fragmented Impact Melt (February 25, 2011)
LOLA's Jackson crater (July 11, 2010)

Moore F Impact Melt (October 30, 2009)

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