Post by Scott Mest, Planetary Science Institute, Tucson, AZ 85719, USA.
Lunar sinuous rilles (German for ‘groove’) consist of long, narrow depressions in the lunar surface that meander in a curved path across the surface and morphologically resemble terrestrial fluvial channels (Image 1). Sinuous rilles are generally up to several kilometers wide and hundreds of kilometers in length. On the Moon, sinuous rilles are found within volcanic terrains such as the extensive lunar mare. Their morphology and association with volcanic deposits suggests that they are the remains of lava channels or collapsed lava tubes.
Unlike much of the lunar nearside, the south polar region of the Moon shows little evidence for volcanic activity. The largest concentration of mare deposits in this area are found along the eastern limb (near 90°E), and several impact crates and basins, such as Schrödinger basin, contain mare deposits on their floors.
The floor of Schrödinger consists primarily of plains materials that display a variety of surface textures and albedos. These materials have been interpreted to be impact-related materials (e.g., Schrödinger impact melt, ejecta deposits from nearby craters), mare deposits, or pyroclastic deposits (dark feature left of center). Recent geologic mapping using high resolution images from the Lunar Reconnaissance Orbiter Camera (LROC) has been able to constrain the spatial extents of the deposits on Schrödinger’s floor, as well as identify previously unseen features that can be used to constrain the origins of these deposits.
Image 1 shows a previously unobserved sinuous rille that cuts across part of the floor in central Schrödinger. Image data from previous missions (e.g., Lunar Orbiter, Clementine) are lower in resolution than images from the LROC narrow-angle camera and small features such as this rille remained undetected. This rille is approximately 30 km long and extends beyond the boundaries of this image. The rille cuts through dark plains material, that is interpreted to be basaltic in composition, as well as adjacent hilly terrain that may be volcanic in nature (likely basalt) or impact melt from the Schrödinger impact event. The presence of this rille provides evidence that at least some of the materials on the floor of Schrödinger basin is volcanic in nature. Rigorous analysis of additional high-resolution LROC images will enable more previously unobserved features to be discovered.
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