Boulder Mound

Boulder rich mound on the northeastern rim of Dawes crater. Image width is 500 m, sunlight is from the image bottom. LROC NAC M139734469L [NASA/GSFC/Arizona State University].

Today's Featured image focuses on an extremely boulder rich mound, located about 100 m east of the rim of Dawes crater. Dawes crater is 18 km in diameter and located at the boundary between Mare Serenitatis and Mare Tranquillitatis.

The diameter of the mound is about 150 meters. From the appearance of relatively fresh fragments clustering within a circular area, one gigantic boulder likely hit the ground and fragmented to make this mound. But it did not hit hard enough to make a crater, so we can infer that the impact velocity was low. Then the question is, where did that gigantic boulder came from?

LROC WAC 100 m/pixel monochrome mosaic of the boundary of Mare Serenitatis and Mare Tranquillitatis. Image center is latitude 17.226deg N, longitude 26.414deg E. Yellow arrow and blue square indicate today's Featured Image and NAC footprint  [NASA/GSFC/Arizona State University].

Since this bouldery mound is beside an 18 km diameter crater, huge boulders could have been thrown out as a part of its ejecta. But in the case of this mound, the landing must have been at the end of the ejecta emplacement, otherwise it would have been buried. Why did it land late in the sequence of ejecta emplacement? Another source crater might have supplied this huge boulder. If so, that second crater must be nearby to keep the impact velocity low. 

Explore other boulder rich mounds and search for a possible source crater in the full NAC frame yourself!

Related posts:
Zebra Stripes, Impact melt in Anaxagoras crater, Bright ridge near Mons Hansteen, Buckland Boulders, Fragmented Impact Melt, Mounds in a melt pond


Posted by Hiroyuki Sato on November 15, 2011 11:27.