Splash Mark

Meandering line of boulders at the bottom of Necho crater. Image width is 690 m, LROC NAC M167390131L. Sunlight is from left side [NASA/GSFC/Arizona State University]

Today's Featured Image highlights the southern edge of an impact melt pond, located on the floor of Necho crater. Necho is a relatively young, Copernican-aged crater (meaning, it formed between ~1.1 billion years ago and the present) with a diameter of 30 km, located on the farside of the Moon (5.25°S, 123.24°E). As seen in the WAC context image below, the crater floor is filled by impact melts. The meandering line of boulders in the opening image was found near the bottom of a north to northeast facing slope. There is no clear relief or texture difference on the surface except this boulder line. How was it formed?

Necho crater and its surroundings in WAC monochrome mosaic (100 m/pix). Image center is 5.25°S, 123.31°E. The locations of full NAC frame (blue box) and today's Featured Image (yellow arrow) are indicated [NASA/GSFC/Arizona State University].

Probably this line of boulders was formed as a splash mark or wave front coming from the melt pond, driven by secondary impacts or debris dumped into the melt pond. In fact, impact melt flows frequently retain similar boulder lines along the edge of each flow unit (see Scalelike Impact Melts, A molten flood). Also, discontinuous boulder marks at the upper part of this image extend downslope, near the relatively level melt pond area, which might be a side of the splash flow. 

Explore the full NAC view of Necho's impact melt pond yourself!

Related Posts:
Necho Crater
Scalelike Impact Melts
Waves
Impact melt in Anaxagoras crater
A molten flood


Posted by Hiroyuki Sato on July 31, 2012 09:19.