Physical properties and structural evolution of asteroids

Abstract

Asteroids are thought to harbor an abundance of valuable mineral resources, and the original materials that were present in the early solar system. The information contained in these small bodies could provide us with critical clues about how the planets formed as well as life started on the Earth. With the help of observations and the data returned by several successful asteroid missions, the progression of asteroid research has been expanded from understanding the asteroids’ orbits, shapes, rotation states and spectral classes to exploring more details about their internal structures and how they evolve in response to external effects. Among all the possible forms of asteroids’ structures, the rubble-pile structure provides an interesting insight about how asteroids’ structures evolve and a reasonable explanation for some observations. However, the discrete and low-strength characteristics of this structure raise many open questions to understanding its evolution, identifying its physical properties, and designing future asteroid missions. Based on the orbital distribution and the observed physical properties of asteroids, this study attempts to draw a whole picture on how asteroids’ structure evolves and demonstrates the reasons why most asteroids above 300 m size scale should possess rubble-pile structures. From the perspective of the physics of granular mechanics, a review of progress in investigating the structural characteristics and the dynamical evolution mechanisms of rubble-pile asteroids is present. A thorough comparative analysis on the efforts made by different methods shows that, theoretical analyses and laboratory experiments suffer from the limitation of applications and high economic cost, respectively, while numerical modeling techniques can efficiently serve many purposes. Among all the numerical methods, the discrete element method can retain the discrete nature of rubble-pile structures and can be used to analyze both static and dynamic processes. Some basic problems and potential research interests related to the application of discrete element method on rubble-pile asteroids are suggested.