Impact melt, rock that is melted by the tremendous energy released during an impact cratering event, results in fascinating morphologies visible in many NAC images. Most melt stays inside the crater, freezing into melt-ponds, but some is thrown out of the crater and flows down the exterior ejecta blanket until it is completely solidified by surface cooling.
Today's Featured Image explores a fantastic impact melt deposit on the southern rim slope of Petavius B, about 2.5 km away from the rim. The flat floored arc-shaped area at the bottom of this image was likely a pool of melt that drained out of the channel at the top. The shadows highlight the depth and steep banks of the channel.
Similar morphologies are found within terrestrial lava flows, but the terrestrial examples often have distinctive cracks as lava backs up beneath a crust forming tumuli or pressure ridges. Why do we not see similar structures on the Moon? This is a mystery, but perhaps the impact melts have lower viscosities or different cooling processes than the lava on Earth!
Open up the full NAC frame and find more fascinating impact melt features by yourself!
Posted by Hiroyuki Sato on February 14, 2012 11:19.