Chappelow J E
Meteorifics Inc., 1148 Sundance Loop, Fairbanks, Alaska 99709, USA.
Meteorit Planet Sci. 2018 Apr;53(4):813-825. doi: 10.1111/maps.12853. Epub 2017 Mar 27.
Recent work on the shapes of small, simple impact craters on the Moon has shown that the parabolic ideal does not well represent the vast majority of these craters. They are hyperbolic in shape and usually resemble a cone more than a parabola. A parabolic shape also does not fit the most commonly held archetype for simple craters in general (Linné), which is also hyperbolic. In addition, Linné itself may not be the best model for fresh simple craters, in terms of cross-sectional shape, although shape data to compare it to have heretofore been lacking. Here, the "free shadowfront method" for determining the shapes of simple craters is used to measure 64 fresh simple craters on five lunar maria to test both assumptions. Laser altimetry cross sections, available for many of the craters measured herein, are used to complement and spot-check the shadow measurement results, and thereby demonstrate the efficacy of the free shadowfront method. A new shape model is established, and two craters that better fit this model than Linné are identified. These are located at 24.45° N/328.12° E and 31.35° N/296.46° E and have diameters of 1.40 and 2.73 km, respectively. An apparent dichotomy between fresh simple craters smaller than 2.5 km and those larger than this is observed. Flat floors are found to be ubiquitous among the larger craters, but rare and small in extent in smaller ones. A slide in one crater which appears to be an incipient flat floor suggests a major mode of formation for these flat floors.
近期对月球上小型简单撞击坑形状的研究表明，抛物线理想模型并不能很好地代表这些撞击坑中的绝大多数。它们的形状是双曲线形的，通常更像圆锥而非抛物线。一般来说，抛物线形状也不符合简单撞击坑（林奈撞击坑）最普遍的原型，其也是双曲线形的。此外，就横截面形状而言，林奈撞击坑本身可能并非新鲜简单撞击坑的最佳模型，尽管此前一直缺乏可与之比较的形状数据。在此，使用“自由阴影前沿法”来确定简单撞击坑的形状，以测量五个月海区域的64个新鲜简单撞击坑，从而检验这两个假设。本文测量的许多撞击坑都有激光测高横截面数据，用于补充和抽查阴影测量结果，进而证明自由阴影前沿法的有效性。建立了一个新的形状模型，并识别出两个比林奈撞击坑更符合该模型的撞击坑。它们分别位于北纬24.45°/东经328.12°和北纬31.35°/东经296.46°，直径分别为1.40千米和2.73千米。观察到直径小于2.5千米的新鲜简单撞击坑与直径大于2.5千米的撞击坑之间存在明显差异。发现平坦的坑底在较大的撞击坑中普遍存在，但在较小的撞击坑中很少见且范围较小。一个撞击坑内似乎是初始平坦坑底的滑坡表明了这些平坦坑底的一种主要形成方式。
