SGER: Fracture Processes on Small Extraterrestrial Bodies in the Solar System

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Leonid GermanovichGeorgia Institute of TechnologySGER: Fracture Processes on Small Extraterrestrial Bodies in the Solar System"Traditionally, asteroids and comets are considered to be an important source of information on the early Solar System. The defense against asteroids and comets has become a popular media and research topic. They pose a risk to life on Earth, but also represent a potential source of metals and other raw materials in the near-Earth space. The vast majority of data concerning asteroids and comets has been obtained via remote observations based on the assumed surface properties, which are functions of former and ongoing geomechanical processes. Yet, there has been no or hardly any quantification and mathematical treatment of the possible role of these processes in the evolution of asteroids and comets.The goal of this proposal is to incorporate principles of terrestrial geomechanics in the framework of mechanical processes that occur on asteroids and comets. Geomechanical processes on terrestrial planets (i.e., Mercury, Venus, Earth, Moon, and Mars) are significantly affected by such factors as gravitation, tectonics, volcanism, and erosion, which are considered absent, or of no consequence, on small extraterrestrial bodies. In essence, asteroids represent the simplest geomechanical systems (no air, no water, extremely low gravity, "primitive" rocks) and studying this extreme case would not only assist astronomical developments but could also provide valuable feedback for conventional (terrestrial) geomechanics.The proposed research consists of three parts: (1) devising a new mathematical model accounting for various temporal and spatial scales associated with fracture processes on asteroids; (2) investigating mechanics of the formation of the soil (regolith) on asteroids; and (3) developing a new model of cometary outbursts associated with fractional sublimation of nucleus material. It is suggested that thermal stresses induced by the "seasonal" periodic heating due to the motion of the asteroid around the Sun in elliptical orbits coupled with short "daily" rotations around the axis of inertia are primarily responsible for the disintegration of asteroid material. Furthermore, the regolith/soil formation is an ongoing process caused by thermal space weathering, which is an effective means of erosion even in the airless, waterless, and low-gravity environment. Finally, sublimation of cometary material caused by crystallization of amorphous ice produces large hydraulic fractures. Propagation of these fractures transports pressurized vapor-dust emulsions to the surface of the comet nucleus resulting in catastrophic vapor-dust outbursts.