LROC: Pyroclastic Trails

Northeastern rim of unnamed crater 340 km southeast of Copernicus, among the Schröter and Gambart crater groups in Southern Sinus Aestuum (5.65°N, 8.71°W). A 612 meter-wide field of view from LROC Narrow Angle Camera (NAC) observation M144680787R, spacecraft orbit 6455, November 18, 2010; angle of incidence 49.39° at an original 50 cm per pixel resolution from 46.42 km. Downslope is to the bottom-right, view the original 1200 x 1200 LROC Featured Image HERE [NASA/GSFC/Arizona State University]

Hiroyuki Sato
LROC News System

The pyroclastic Southern Sinus Aestuum (5.42°N, 351.36°E) is famous for extensive dark mantle deposits (DMD), materials which have the lowest albedo (or highest optical maturity, or 'OMAT') on the Moon.

The DMD were likely formed as explosive eruptions threw out a blanket of small particles (pyroclasts).

Today's Featured Image shows a portion of unnamed crater rim located inside this DMD unit, about 2.4 km in diameter, with 4 or 5 dark streaks on its slope (see the crater's full profile in the NAC mosaic below).

The opening image highlights one of the sources for a dark streak. The right half of the image is the crater wall, and the left half is the surrounding flat area. The streak originates at nearly the top portion of the crater wall and extends down the slope. Notice that the streak is darker than the surrounding flat area some buried low reflectance materials were exposed on the middle of the slope and slid downhill.

Zoom out view of a mosaic of both the right and left frames of LROC NAC observation M144680787 (M144680787R and M144680787L). About a 3.93 km-wide field of view, sunlight from the east. Blue box indicates the location of the area shown in the LROC Featured Image released September 6, 2012. View the full size context image HERE [NASA/GSFC/Arizona State University].

Actually, the albedo around this unnamed crater is not as low as the main DMD area. The contrast is very, small but you can see a slightly higher albedo halo around the crater in the WAC context image. The dark streaks inside this crater all originate from almost the same level of the crater wall. Probably this unnamed crater excavated higher reflectance bedrock under the DMD, and spread it around the crater. Then the pyroclastic materials exposed in the wall (sandwiched between the bedrock and the ejecta) slumped down the crater wall leaving the dark streaks.

Careful investigations of the craters in the DMD by NAC images are quite useful to understand the thickness, the volume, and formation process of DMD. More and more NAC observations of DMD are expected. 

Southern Sinus Aestuum in context with Copernicus, 340 km away. Note dark streaks from rim to floor are also a feature of nearby Schröter D crater. LROC WAC monochrome mosaic (100 m/pix) centered on the subject unnamed crater (arrow), draped over LOLA altimetry data using the NASA LMMP ILIADS application  [NASA/LMMP/GSFC/Arizona State University].

Explore this pyroclastic slides by full NAC frame yourself, HERE.

Related Posts:
Dark streaks in Diophantus crater
Dark Craters on a Bright Ejecta Blanket
Alphonsus crater mantled floor fracture
Dark-haloed crater in Mare Humorum
Pyroclastic Excavation

Pyroclastic Southern Sinus Aestuum, including the unnamed crater of interest at center, as seen from Earth. 4100 x 5000 pixel Mosaic of the Moon captured by Astronominsk, August 8, 2012.