Comparative study of the surface roughness of small bodies in the Solar System

Abstract

Surface roughness can indicate the material and structure of a planetary body depending on the scale. Small scales give insights on the physical properties of the regolith, mid-scale can point out regional units and related evolutionary processes and the interior structure might be implied at a global scales. Previous roughness studies of asteroids were done by different techniques and over different scales. This work aimed for a consistent approach over the same scales of 1, 5, 10 and 19 m, so that the asteroids can be reliably compared. The small bodies of interest in this comparative study are 433 Eros, 25143 Itokawa, 101955 Bennu, 162173 Ryugu, 65803 Didymos and 65803-1 Dimorphos. The used method is Roughness from Shape (RFS) which is based on the relation of angles of the facets on a shape model. Unfortunately, Eros could only be studied at 19 m scale due to low resolution of the shape model, while Didymos’ results seem suspiciously smooth. However, roughness maps were produced for each individual body at respective scales and were studied in the view of matching morphological features, especially craters and boulders seem to correlate. Further, the results were compared to previous studies and the global mean/median roughness and roughness distribution were statistically analyzed. Most rubble-pile asteroids show similar mean/median values in contrast to the lower roughness on the fractured monolith Eros. The roughness distribution could be fitted with an Exponentiated Weibull function which indicates that the roughness is related to fragmentation processes. Overall, the results suggest that the formation process shaped the surface of the small bodies more than the asteroid’s properties.