Asymmetrical distribution of rayed craters on the Moon
Asymmetrical distribution of rayed craters on the Moon
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DOI：
10.1016/s0012-821x(02)01111-1
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发表时间：
2003-02
影响因子：
5.3
通讯作者：
T. Morota;M. Furumoto
中科院分区：
文献类型：
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作者：
T. Morota;M. Furumoto
卫星的同步旋转应该会导致其表面上的陨石坑率的空间变化。撞击坑密度在轨道运动的顶点处最大，随着距顶点角距离的增加而减小。顶点密度（最大值）与前顶点密度（最小值）之比取决于撞击物与卫星相遇的平均速度。虽然月球也处于同步自转的状态，但据推测，月球上陨石坑密度的不对称性很难观察到。我们在这里报告的空间变化的射线陨石坑的密度在月球上，这可能与同步旋转。由于射线的寿命相对较短（<8亿年），因此结果提供了有关最近撞击的信息。克莱门汀750纳米镶嵌图像上的射线陨石坑。我们调查了从42°N到42°S的低纬度地区的陨石坑。为了避免物质差异对射线保存的影响，我们分析了东经70° ~ 290°E高原上的陨石坑。在1.4× 107 km ~ 2的研究区域内，共发现222个直径大于5 km的射线撞击坑。射线坑的平均密度，在领先的一面是远远高于在拖尾侧。弹坑密度随着距顶点的角距离的正弦函数而减小。观察到的顶点处的密度与前顶点处的密度之比约为1.5。这一比例表明，月球上最近的陨石坑主要是由近地小行星形成的，而不是具有更高碰撞速度的彗星。
The synchronous rotation of the satellite ought to cause a spatial variation in the cratering rate over its surface. The crater density is expected to be maximum at the apex of the orbital motion and decrease with the increase of the angular distance from the apex. The ratio of the density at the apex (maximum) to that of the antapex (minimum) depends on the average encounter velocity of impactors to the satellite. Although the Moon is also in a state of the synchronous rotation, it has been supposed that the asymmetry in the crater density on the Moon can be hardly observed. We report here a spatial variation in the density of rayed craters on the Moon, which may be associated with the synchronous rotation. Since the lifetime of a ray is relatively short (<0.8 billion years), the results provide information on recent impacts. Rayed craters are identified on Clementine 750-nm mosaic images. We investigate craters in a lower latitude zone from 42°N to 42°S. To avoid an effect of material difference on the ray preservation, we analyze craters on the highland from 70°E to 290°E in east longitude. A total of 222 rayed craters larger than 5 km in diameter are identified in the study area of about 1.4×107km2. The average density of rayed craters on the leading side is substantially higher than that on the trailing side. The crater density decreases as a sinusoidal function of the angular distance from the apex. The observed ratio of the density at the apex to that at the antapex is about 1.5. The ratio suggests that recent craters on the Moon are formed mainly by near-Earth asteroids rather than comets with higher encounter velocities.