Small Crater Ejecta

Fifty meter diameter crater with a bright ejecta blanket that extends several crater radii. The darker interior of the crater could be a melt pond. Image width is 1000 m, LROC NAC M1117189620R [NASA/GSFC/Arizona State University].

Our impressions (and interpretations) of surface features on planetary bodies are affected by the way they interact with sunlight when we image them. For instance, the shape of a crater is brought out by shadows in large incidence angle (Sun near the horizon) images. In today’s Featured Image, we are observing a crater with the Sun nearly directly above the surface. This type of image (small incidence angle) helps scientists understand the physical properties of the surface. Why might the ejecta blanket of the crater be highly reflective? Why is the interior have a much lower reflectance? Two different surface properties could be affecting what we see. First, 'fresh' material should be brighter than surrounding material. And second, the composition of materials affects how they reflect light (see albedo). 

LROC WAC context mosaic of today’s Featured Image, near the red asterisk (3.022° N, 258.698° E). Image width is 100 km [NASA/GSFC/Arizona State University].

In the case of today's Featured Image, the crater looks very young. We have some stratigraphic evidence for this as the crater is sitting on top of a larger flesh unnamed crater's ejecta deposit (see context image). Therefore the brightness of the ejecta blanket is likely due to the young nature of the crater! But that doesn't solve the problem of the crater's interior. The interior could have been mantled by a thin veneer of impact melt which then pooled in the center. We know from many examples that impact melt rock reflects less light than its source material. The impact melt hypothesis is not certain, though a follow up image at a larger incidence angle to help us understand morphology and could certainly help test this hypothesis!

Explore more ejecta in full the NAC frame! 

Related Posts:

Ejecta Starburst

Swept Surface

Symmetric Ejecta

Published by Drew Enns on 28 March 2013