Wednesday, August 1, 2012

LROC: Impacts on the Impact Melts

Impact melt surface ejected from Necho crater. Field of view width is 620 meters, LROC Narrow Angle Camera (NAC) observation M134374642L, LRO orbit 4936, July 21, 2010; Sunlight from the west, angle of incidence 68.85° at 0.62 meters resolution from 59.98 km. View the larger original LROC Featured Image HERE [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

Today's Featured Image looks vaguely like a microscope picture of onion cells (complete with a nucleus and cell walls), but in reality this is an impact melt deposit that extends out of Necho crater (5.25°S, 123.24°E; see whole view of this melt sheet HERE).

In between the network shaped cracks (notice that the sunlight is from left of the image, thus lineations are negative relief), multiple strangely-shaped craters with a central dent surrounded by a flat moat about 15 to 40 m in diameter are observed. They resemble bench craters (e.g. Fresh Bench Crater in Oceanus Procellarum, Bench Crater in Plato), except that they are not quite circular in shape and no radial ejecta is visible. The relatively bigger one near the image center has deeper dent and a petal shaped system of exterior deposits.

Full size field of view in the LROC Featured Image in context with the larger NAC frame M134374642L at roughly 4 meters per pixel resolution, shows some of the complexity of the impact melt on the east flank of Necho [NASA/GSFC/Arizona State University],
Necho crater and its eastern side, dominated by its ejecta deposits,  in viewed on the digital terrain model available in the Google Earth application, overlaid with the 604nm monochrome data from LROC Wide Angle Camera observation M165041995C, LRO orbit 9456, July 11, 2011; resolution 86.15 meters from 61.3 km. The locations of full NAC frame (blue box) and the field of view, highlighted in the LROC Featured Image (yellow arrow, 4.79°S, 124.125°E) are indicated [NASA/GSFC/Arizona State University].
These strangely-shaped craters are probably self-secondary craters, formed after the emplacement of the impact melt deposit but before the complete solidification of the molten rocks. The physical properties of unsolidified target might have resulted in these distinctly-shaped craters.

Explore more strangely-shaped craters on Necho's impact melts in the full LROC NAC image, HERE.

Related Posts:
Splash Mark at Necho crater (July 31, 2012)
Fresh Bench Crater in Oceanus Procellarum (December 23, 2011)
Bench Crater in Plato (November 9, 2011)
Impact melt at Necho crater (September 1, 2010)
A molten flood (July 28, 2010)
Necho Crater (August 22, 2009)

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