Fine-grained regolith, a surface layer of unconsolidated granular material, has been considered to cover the surfaces of airless bodies and determine their spectral and thermophysical properties. However, surfaces of asteroids visited by recent sample return missions are dominated by centimetre- to metre-sized boulders, indicating an active fine-grained regolith removal process at work. To understand asteroid regolith evolution, we apply recent space and laboratory experimental results to simulate regolith fragmentation processes, loss by impact ejecta, and electrostatic removal of fine-grained regolith. Here we show that coarse, boulder-rich scenery probably emerges on kilometre-sized and smaller asteroids within a few million years, as the electrostatic removal of fine-grained regolith dominates production by fragmentation. Surface thermal inertia enhancement associated with fine-grained regolith loss on small main-belt asteroids increases the Yarkovsky drift and the probability of orbital excursion to the near-Earth environment through resonances with giant planets. We suggest that the competition between electrostatic erosion and space weathering shapes the appearance of reflectance spectra of small asteroids, related to the size, spatial and spectral distributions of S-complex asteroids.

细粒风化层是松散颗粒材料的表面层，被认为覆盖了无气物体的表面并确定了它们的光谱和热物理特性。然而，最近的样本返回任务访问的小行星表面主要是厘米到米大小的巨石，这表明正在进行一个活跃的细粒风化层清除过程。为了了解小行星风化层的演化，我们应用最近的空间和实验室实验结果来模拟风化层碎裂过程、撞击喷射物的损失以及细粒风化层的静电去除。在这里，我们展示了粗糙的、富含巨石的景观可能会在几百万年内出现在千米大小和更小的小行星上，因为细粒风化层的静电去除主导了破碎的生产。与小型主带小行星上细粒风化层损失相关的表面热惯性增强增加了 Yarkovsky 漂移和通过与巨行星共振而轨道偏移到近地环境的可能性。我们认为静电侵蚀和空间风化之间的竞争塑造了小型小行星反射光谱的外观，这与 S 复合小行星的大小、空间和光谱分布有关。