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The Boulder Population of Asteroid 4 Vesta: Size‐Frequency Distribution and Survival Time
Earth and Space Science ( IF 3.1 ) Pub Date : 2020-11-03 , DOI: 10.1029/2019ea000941
Stefan E. Schröder 1 , Uri Carsenty 1 , Ernst Hauber 1 , Franziska Schulzeck 1 , Carol A. Raymond 2 , Christopher T. Russell 3
Affiliation  

Dawn's framing camera observed boulders on the surface of Vesta when the spacecraftwas in its lowest orbit (Low Altitude Mapping Orbit, LAMO). We identified, measured, and mapped boulders in LAMO images, which have a scale of 20 m per pixel. We estimate that our sample is virtually complete down to a boulder size of 4 pixels (80 m). The largest boulder is a 400 m‐sized block on the Marcia crater floor. Relatively few boulders reside in a large area of relatively low albedo, surmised to be the carbon‐rich ejecta of the Veneneia basin, either because boulders form less easily here or live shorter. By comparing the density of boulders around craters with a known age, we find that the maximum boulder lifetime is about 300 Ma. The boulder size‐frequency distribution (SFD) is generally assumed to follow a power law. We fit power laws to the Vesta SFD by means of the maximum likelihood method, but they do not fit well. Our analysis of power law exponents for boulders on other small Solar System bodies suggests that the derived exponent is primarily a function of boulder size range. The Weibull distribution mimics this behavior and fits the Vesta boulder SFD well. The Weibull distribution is often encountered in rock grinding experiments and may result from the fractal nature of cracks propagating in the rock interior. We propose that, in general, the SFD of particles (including boulders) on the surface of small bodies follows a Weibull distribution rather than a power law.

中文翻译:

小行星4 Vesta的巨石种群:大小频率分布和生存时间

当航天器处于最低轨道(低海拔制图轨道,LAMO)时,Dawn的成帧相机观察到Vesta表面的巨石。我们在LAMO图像中识别,测量和绘制了巨石,每个像素的大小为20 m。我们估计我们的样本实际上可以完整地缩小到4像素(80 m)的巨石尺寸。最大的巨石是Marcia火山口层上一个400 m大小的地块。相对来说,在大的相对较低的反照率地区中,巨石很少,据推测是威尼斯地区盆地的富碳射出物,因为巨石在这里不那么容易形成或寿命较短。通过比较已知年龄的陨石坑周围的巨石密度,我们发现最大巨石寿命约为300 Ma。通常假定巨石大小频率分布(SFD)遵循幂定律。我们通过最大似然法将功率定律适用于Vesta SFD,但它们不太适合。我们对其他小型太阳系天体上巨石的幂律指数的分析表明,得出的指数主要是巨石尺寸范围的函数。Weibull分布模仿了这种行为,非常适合Vesta boulder SFD。威布尔分布在岩石磨削实验中经常遇到,并且可能是由于岩石内部传播的裂纹的分形特性造成的。我们建议,一般而言,小物体表面上的颗粒(包括巨石)的SFD遵循威布尔分布而不是幂定律。我们对其他小型太阳系天体上巨石的幂律指数的分析表明,得出的指数主要是巨石尺寸范围的函数。Weibull分布模仿了这种行为,非常适合Vesta boulder SFD。威布尔分布在岩石磨削实验中经常遇到,并且可能是由于岩石内部传播的裂纹的分形特性造成的。我们建议,一般而言,小物体表面上的颗粒(包括巨石)的SFD遵循威布尔分布而不是幂定律。我们对其他小型太阳系天体上巨石的幂律指数的分析表明,得出的指数主要是巨石尺寸范围的函数。Weibull分布模仿了这种行为,非常适合Vesta boulder SFD。威布尔分布在岩石磨削实验中经常遇到,并且可能是由于岩石内部传播的裂纹的分形特性造成的。我们建议,一般而言,小物体表面上的颗粒(包括巨石)的SFD遵循威布尔分布而不是幂定律。
更新日期:2020-11-03
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