Orientale Sculpture

An oblique view of ejecta from the Orientale basin, over 400 km south of the basin rim. Scene is approximately 5 km across, centered at 51.8°S, 264.8°E, NAC images M1127819355L & R [NASA/GSFC/Arizona State University].

Today's featured image is located near the center of the ancient 600-km Mendel-Rydberg basin. Its degraded state means Mendel-Rydberg's presence is not obvious in the WAC context image below (in fact, its existence was only confirmed in 1994 with Clementine topography data), but its western rim is near the crater Mendel, and Rydberg and Guthnick craters are near the center of the basin. However, it was not the Mendel-Rydberg impact that was responsible for the ups and downs in the hummocky deposits seen in today's Featured Image, but the Orientale impact event, hundreds of kilometers away to the north.

Ejecta from impact basins is both erosional, gouging out long valleys and leaving strings of large secondary craters (along the arrows in the image below), and depositional, blanketing even distant terrain with material excavated from the impact site. Basin ejecta plays such a large role shaping the lunar surface that these ups and downs are often referred to as "basin sculpture," and the ejecta from Orientale (below) certainly sculpted the terrain in today's image.

LROC WAC context views of the southern Orientale region. The blue box in the image on the left shows the location of the scene on the right; the yellow box shows the approximate location of today's featured image. Click to enlarge [NASA/GSFC/Arizona State University].

The hummocky deposits that cover low-lying areas in the top image, and the image below, are likely ejecta from the Orientale basin. These low-lying regions may have once been exposures of smooth mare basalt, some of which is still exposed on the surface in nearby regions, but are now hidden under a blanket of debris from Orientale. Buried volcanic deposits such as these are known as "cryptomare" and tracking down the locations of these ancient sites of volcanic activity is key for understanding the extent of early volcanism on the Moon.

A wider (reduced-resolution) view of today's featured image within the Mendel-Rydberg basin. NAC images M1127819355L & R [NASA/GSFC/Arizona State University].

You may also note that the hills in the southern portion (right side) of the image above have a lumpy texture, also visible in the WAC context image. This is also likely due to Orientale's influence - the result of a massive ground hugging flow of ejecta that piled up on the sloped terrain. This oblique view of the region gives a great perspective on its complex history that would have been compelling enough with just the ancient Mendel-Rydberg basin and early lunar volcanism, but the spectacular basin ejecta flows captured here are just icing on the cake (so to speak). 

Explore the full-resolution view below. 

Related Featured Images:

Amazing Orientale Peaks and Valleys

Regolith Patterns in Mendel-Rydberg

Window to the Farside Mantle

Two-toned Impact Crater in Balmer Basin: A reflection of the Target?

Dark Craters on a Bright Ejecta Blanket


Published by Brett Denevi on 30 July 2013