53-7 Simulating Breccia Formation: Hypervelocity Impacts on Lunar Regolith

Abstract:

The hypervelocity impact experiments on Lunar Highland Simulant-1 (LHS-1) offer a compelling geological analogy for the formation of breccias on the Moon. Projectiles were launched at speeds at or near the Moon's escape velocity of 2.38 km/s, mimicking the high-energy impacts of meteorite ejecta. The kinetic energy (KE) of these projectiles, ranging from 240 J to 1680 J, was sufficient not only to halt their progress but also to induce significant changes in the target material. These impacts yielded friable lithic fragments measuring between 3 and 20 mm and a dense, 1.4-cm-diameter lithic plug. The fragments and plugs were easily comminuted and disintegrated into their constituent grains, providing physical evidence that intense pressure from hypervelocity impacts can compact loose regolith particles and "weld" them together to form new composite rock structures. This process is analogous to the shock metamorphism that occurs during natural meteorite impacts, where shock pressure waves travel through the regolith, causing varying levels of metamorphic change from melting to fracturing and brecciation. The presence of these impact-generated structures in the tests supports the theory that meteorite bombardment is a key process in the formation of lunar breccias, a dominant rock type found across the lunar highlands, and offers valuable insights into the ongoing geological activity on the Moon.

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