Left panel: the spatial distribution of boulders on the Abydos site, where Philae is identified by a yellow circle. Boulders smaller than 1.7 m, where the boulder size corresponds to the length calculated from the corresponding area, are shown in yellow and are not taken into account in the statistic. Right panel: the cumulative size-frequency distribution of boulders larger than 1.7 m identified on the Abydos site. The bin size is 34 cm, and vertical error bars indicate the root of the cumulative number of counting boulders (as in Michikami et al. 2008). The fitting regression line gives a power-law index of −4.0 + 0.3/−0.4.