Science and Exploration

Dry Debris or Liquid Flow on The Moon?

By Keith Cowing
Status Report
September 28, 2016
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Dry Debris or Liquid Flow on The Moon?
Stevinus A

Stevinus A (31.75°S, 51.55°E) is an 8 km diameter crater with very smooth, high albedo crater walls and low albedo streamers and streaks.

The high albedo material composing the crater walls may have once been an impact melt veneer that is eroding over time as micrometeorite bombardment promotes regolith formation. Sometimes, craters with smooth walls are observed because the craters are old enough (at least Eratosthenian age, where their ejecta rays have been erased) to have developed a regolith layer that blankets the interior of the crater and obscures small-scale morphology variations. However, Stevinus A is pretty young and has only recently begun to accumulate a thin regolith because there are distinct edges observed (above the boulder mentioned in the opening image, for example) as well as boulder trails (also observed in the opening image).

Stevinus A crater is home to many unique features, but the low albedo flows on the crater walls are striking. Are they impact melt flows that splashed onto the crater walls and flowed downhill, toward the crater floor? Or are these flows composed of granular, dry debris that acted like a fluid when the particles were mobilized, perhaps by a seismic shock wave from a nearby impact? Moreover, why are these streamers composed of such low reflectance material when the rest of the crater is of higher albedo?

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