The erosion of lunar soil by rocket exhaust plumes is investigatedexperimentally. This has identified the diffusion-driven flow in the bulk ofthe sand as an important but previously unrecognized mechanism for erosiondynamics. It has also shown that slow regime cratering is governed by therecirculation of sand in the widening geometry of the crater. Scalingrelationships and erosion mechanisms have been characterized in detail for theslow regime. The diffusion-driven flow occurs in both slow and fast regimecratering. Because diffusion-driven flow had been omitted from the lunarerosion theory and from the pressure cratering theory of the Apollo and Vikingera, those theories cannot be entirely correct.
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