Impact Melt Volumes in Simple Lunar Craters: Constraints on Modeling

Introduction: Impact melt is a typical product produced during the cratering process as a result of the intense heating of the target usually because of pressure decompression, but also possible because of shear heating (Figure 1). Melt is observed on all of the terrestrial planets in both simple and complex craters [16]. High-resolution data for the Moon now allows impact melt deposits to be characterized with much greater fidelity than in the past or on the other terrestrial planets as they are imaged at lower resolution (e.g., Mercury and Venus) or have widespread dust coatings (Mars). Recognition that lunar craters as small as ~200 m in diameter have well-defined impact melt deposits on their floors [7] was unexpected, based as consideration of theoretical modeling and consideration that much of the melt would be ejected [8-11]. For craters in the hundreds of meter diameter range, the predicted volume of impact melt was so small that most should have been ejected from the crater and insufficient volume would have been available to pool on the floor. The observation that small diameter craters did have melt, led to the questions of the amount of melt that was present and the extent to which the theoretical models were correct with respect to the amount of melt produced during an impact.