Subset of uncalibrated LROC NAC frame M104447576R showing Vallis Lorca, one of four lobes that make up Aratus CA in western Mare Serenitatis near the Montes Apennius. The Sun is shining from the lower left, image width is 1924 meters [NASA/GSFC/Arizona State University].
Aratus CA is an unusual depression and possible volcanic vent, previously featured in the Apollo Image of the Week. This depression is about 9.5 km long and 3 km wide, located at the termination of a north-south trending wrinkle ridge known as Dorsum Owen. After the mare lavas erupted and cooled, contractional tectonic forces generated wrinkle ridge features. Most lunar scientists think this unique depression is a product of both volcanism and tectonic collapse. Each lobe is distinct, for example, Vallis Lorca is a collapse pit crater, while the lobe to the east named Rima Sung-Mei is a small rille. Stratigraphy and cross-cutting relationships indicate multiple tectonic and volcanic events. The featured image of the Vallis Lorca lobe shows “rings” around the rim, indicative of collapse. Browse the whole NAC image!
The 1.5 m/pixel resolution of this NAC image allows for a detailed view of layered outcrops of mare basalt in the southern wall of Aratus CA. Image width is 1480 meters [NASA/GSFC/Arizona State University].