Small crater in Oceanus Procellarum

This unnamed 740 m diameter crater has bouldery walls and is morphologically similar to many <1 km diameter craters in the mare. Image width is 847 m, LROC NAC M127328861L [NASA/GSFC/Arizona State University].

The LROC NAC has imaged thousands of blocky craters similar to this example found in Oceanus Procellarum. The numerous boulders may be fragments of bedrock, regolith breccias formed by the impact itself, or a combination of both. Since a crater depth of excavation is roughly one tenth its diameter, this small crater has probably distributed material from about 75 meters depth around its rim. Usually, ejecta material on the rim comes from the deepest part of the crater, and ejecta farther away from the crater comes from shallower depths. Thus astronauts can walk towards a crater rim, sampling material from greater depths as the rim is approached in a radial cross-section of the ejecta blanket. As you look at these boulders, you are witnessing a history of the emplacement of this mare. If we could just pick up samples and bring them back to Earth, we could figure out how much time elapsed between mare basalt flows in this area and how much the composition changed with time.

The vast Oceanus Procellarum mare basalts are observed in this portion of LROC Wide Angle Camera monochrome M117895651M. Prominent across the scene are wrinkle ridges and secondary crater clusters. The arrow points to the blocky crater in the opening image [NASA/GSFC/Arizona State University].

How many more blocky craters can you find in the full LROC NAC image?

Related posts: Exposed Boulders in the Aitken Mare

Smooth floor in Copernicus crater

Illumination comparison of a mare crater

Published by Lillian Ostrach on 22 March 2011