Tuesday, November 15, 2011

LROC: Boulder mound high on Dawes rim

Boulder rich mound on the northeastern rim of Dawes crater. Image field of view is 290 meters, under a high early afternoon Sun. LROC Narrow Angle Camera (NAC) M139734469L, LRO orbit 5726, September 21, 2010; incidence angle 20.59° with a resolution of 49.4 centimeters per pixel from 44.12 km. See the full 500 meter field of view HERE [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

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 Wide Angle Camera (WAC) 100 meter monochrome mosaic affixed to LOLA 128 topography in ILIADS simulated oblique perspective from the south and 18 km altitude. The boulder mound seen in the LROC Featured Image rests in a conspicuous interruption in the off-center rise in elevation along the northeast rim [NASA/GSFC/Arizona State University/ILIADS].
Fifty kilometer field of view of oddly-shaped Dawes, LROC WAC 100 meter Global Mosaic on LOLA topography, also from ILIADS, perspective from high above the center of the familiar landmark crater, along the Serenitatis and Tranquillitatis frontier [NASA/GSFC/Arizona State University/ILIADS].
LROC WAC 100 meter monochrome Global Mosaic showing Dawes in the context of the boundary zone, between Mare Serenitatis and Mare Tranquillitatis. Image center is latitude 17.226° N, 26.414° E, and the yellow arrow and blue rectangle indicate the location of the area of interest in the LROC Featured Image, November 15, 2011 and the NAC footprint of M139734469L [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

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