Impacts on the Melts

Impact melt surface ejected from Necho crater. Image width is 620 m, LROC NAC M134374642L. Sunlight is from left side [NASA/GSFC/Arizona State University].

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.

Necho crater and its eastern side of the ejecta deposits in WAC monochrome mosaic (100 m/pix). Image center is 5.15°S, 123.70°E. The locations of full NAC frame (blue box) and today's Featured Image (yellow arrow) 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!

Related Posts:
Impact melt at Necho crater
Necho Crater
Fresh Bench Crater in Oceanus Procellarum
Bench Crater in Plato
A molten flood


Posted by Hiroyuki Sato on August 01, 2012 09:35.