Sometimes You Just Need to Vent

Low reflectance material cascaded down the wall of what is likely a volcanic vent in the southwestern portion of the Orientale basin. Image width is approximately 750 m. LROC NAC image M1150135366 [NASA/GSFC/Arizona State University].


Pyroclastic deposits on the Moon are often identified by a mantled appearance and low reflectance. These deposits are the result of an explosive eruption (or many) that involved a volatile component, likely carbon monoxide. The resulting fine-grained debris, including glass beads like those sampled by Apollo 17, gives the surface a dark, mantled appearance (See WAC image below).

LROC WAC normalized reflectance (643 nm) of the low reflectance pyroclastic annulus on the southwest edge of the Orientale basin. The annulus is approximately 180 km in diameter, the extent of which is indicated by the white dashed circle. The red box denotes the location of the NAC image from which Today's Featured Image was taken [NASA/GSFC/Arizona State University].

So, where did the low reflectance material come from? The low reflectance material from Today's Featured Image flowed down the wall of a kidney-shaped (reniform) depression located at the center of the annulus. The lack of a discernible crater rim and irregular shape make this depression a suspect (See WAC image below). The walls of the depression are steep-sloped, yet the floor is fairly flat, which is best observed in a color-shaded digital terrain model (DTM). Such reniform depressions are observed in other locations across the Moon, such as Sulpicius Gallus, interpreted to be a pyroclastic source vent. If the kidney-shaped depression is the source of the low reflectance material, it is likely that material was ejected from the source vent at high velocity, creating an umbrella-shaped plume and depositing the dark, fine-grained material in a ring around the vent.

LROC WAC image of the irregular, kidney-shaped depression from Today's Featured Image. The depression is ~20 km long by ~10 km wide. Note the subdued appearance of the surrounding terrain [NASA/GSFC/Arizona State University].

Pyroclastic deposits are currently of interest to lunar scientists as a possible resource for future missions to the Moon. Such deposits are rich in hydrogen and helium-3, two potential resources for energy production, and iron and titanium, which have engineering applications. The necessary capabilities for utilizing resources such as these in-situ, or on site, are currently under development. In-situ resource utilization (ISRU) is critical to the future of exploration of areas that would otherwise be beyond our reach, both physically and financially.

Do some investigating of your own with the full NAC!

Related Posts:

Layer of Pyroclastics

Lavoisier Pyroclastics

Pyroclastic Excavation

Pyroclastic Trails

Pyroclastics and Vent

Published by H. Meyer on 15 April 2014