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

“传统上，小行星和彗星被认为是早期太阳系信息的重要来源。对小行星和彗星的防御已经成为一个流行的媒体和研究课题。它们对地球上的生命构成威胁，但也代表了近地空间金属和其他原材料的潜在来源。关于小行星和彗星的绝大多数数据都是通过基于假定的表面性质的远程观测获得的，这些表面性质是以前和正在进行的地质力学过程的函数。然而，对于这些过程在小行星和彗星的演化中可能发挥的作用，还没有或几乎没有任何量化和数学处理。这项提议的目标是将地球地质力学原理纳入小行星和彗星上发生的力学过程的框架中。类地行星（即水星、金星、地球、月球和火星）上的地质力学过程受到诸如引力、构造、火山活动和侵蚀等因素的显著影响，而这些因素在小型地外天体上被认为是不存在的，或者是无足轻重的。从本质上讲，小行星代表了最简单的地质力学系统（没有空气，没有水，重力极低，“原始”岩石），研究这种极端情况不仅有助于天文学的发展，而且可以为传统（地球）地质力学提供有价值的反馈。本研究包括三个部分：(1)建立新的数学模型，考虑小行星断裂过程的不同时空尺度；(2)研究小行星上土壤（风化层）形成的机理；(3)建立了一种与核物质分数升华有关的彗星爆发的新模型。由于小行星在椭圆轨道上绕太阳运动而引起的“季节性”周期性加热加上绕惯性轴的短暂“每日”旋转引起的热应力是小行星物质解体的主要原因。此外，风化层/土壤的形成是一个由热空间风化引起的持续过程，即使在无气、无水、低重力环境下，热空间风化也是一种有效的侵蚀手段。最后，由非晶冰结晶引起的彗星物质升华会产生大的水力裂缝。这些裂缝的传播将加压的蒸汽尘埃乳剂输送到彗星核的表面，导致灾难性的蒸汽尘埃爆发。

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.