Excavating Deposits

A ~250 m diameter crater excavates low reflectance material from beneath the lunar surface. LROC NAC image M185955372R, image width ~1.8 km [NASA/GSFC/Arizona State University].

Amazing ejecta patterns from small, young craters are always something to look at on the lunar surface. Today's Featured Image displays compositional diversity in fresh ejecta. The broad, low-reflectance streaks of material are likely excavated pyroclastic materials. This ~250 m diameter crater is located at 2.162°N, 349.401°E, west of the crater Sommering P. This low-reflectance material is part of a larger area called a Dark Mantle Deposit (DMD). Dark mantle deposits have lower reflectances compared to surrounding mare basalt areas and are also spectrally distinct from mare basalt. In this case, the dark mantle deposit was likely covered by a thin layer of crater ejecta.

The location of the crater in the Featured Image is marked with a white circle. WAC context image is 80 km across [NASA/GSFC/Arizona State University].

The opening image has a low incidence angle of 10° which means the Sun is high in the sky (near local noon). High-sun images are good for revealing differences in the reflectance properties of the surface. Low-sun (large incidence angle) images are better at emphasizing morphology due to topographic shading and shadowing. Incidence angle is the angle between the vector of sunlight and the vector normal to the surface. The WAC context image above has a large incidence angle (taken in early morning) which makes visible the topographic high where the crater was formed. This topographic high is a remnant of highland terrain (kipuka) surrounded by younger mare basalt deposits (smooth, flat areas). There are many other craters on the topographic high that excavate low-reflectance material, which suggests that the whole area is different from the surrounding mare basalt deposits. The high-sun WAC mosaic (below) of the same area shows the locations where the dark mantle deposit is visible. You can learn more about dark mantle deposits here!

WAC 643 nm reflectance mosaic of the same area as the WAC mosaic above (100 m/px). Note the darker material around the area of the topographic high. Image is 80 km across [NASA/GSFC/Arizona State University].

Explore the full NAC image to see the other craters excavating low-reflectance material! 

Related Images:

Hyginus Crater and Pyroclastics

Dark Wisps in Copernicus

Polka-Dot Ejecta

Pyroclastic Excavation

Published by Sarah Braden on 3 September 2013