When dust, pebbles, rocks, and boulders act like liquid


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The science team of Lunar Reconnaissance Orbiter released an intriguing picture yesterday of what scientists call a granular flow down the side of a five mile wide crater on the far side of the moon. Looking at the image, one would swear that the darker material flowing down the slope of the crater rim is a lava flow frozen in place.

lunar granular flow

However, according to the scientists, that is not what it is. Instead, this is merely debris left behind from an avalanche.

This location most likely means that we are not observing a compositional difference, as there are no nearby sources of mare basalt that could account for the low-reflectance material. Second, in this particular NAC frame there is no evidence for impact melt deposits around the rim of the crater, although you can find evidence of impact melt in the crater floor. The crater is not large enough to develop terraces where impact melt can pool and then flow out. So this flow is probably granular, not molten.

What I like is how liquid-like the flow looks, especially once it reaches the crater floor and begins to fan out. As the lunar scientists note on another page explaining granular flows, “It is amazing how the physics of wet material (Newtonian flow) in some cases applies to dry material! The Moon is dry and this slide was formed without the involvement of water.”

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