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

列昂尼德·格奥尔基维奇佐治亚理工学院SGER：太阳系中小型地外天体的断裂过程“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。防御小行星和彗星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，但也是近地空间金属和其他原材料的潜在来源。绝大多数有关小行星和彗星的数据都是根据假设的表面特性通过远程观测获得的，这些特性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演化过程中可能发挥的作用，没有或几乎没有任何量化和数学处理办法，本提案的目的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。类地行星上的地质力学过程（即，水星、金星、地球、月球和火星）受到引力、构造、火山活动和侵蚀等因素的显著影响，这些因素在小型外星天体上被认为是不存在的，或者没有影响。本质上，小行星代表了最简单的地质力学系统（没有空气，没有水，极低的重力，“原始”岩石），研究这种极端情况不仅有助于天文学的发展，而且还可以为传统的天文学提供有价值的反馈。（陆地）地质力学。拟议的研究包括三个部分：（1）设计一个新的数学模型，说明与小行星断裂过程有关的各种时间和空间尺度;（2）研究小行星上土壤（风化层）形成的机制;（3）建立一个与核物质部分升华有关的彗星爆发的新模型。据认为，小行星在椭圆轨道上围绕太阳运动，加上围绕惯性轴的“每日”短暂旋转，造成“季节性”周期性加热，由此产生的热应力是造成小行星物质解体的主要原因。此外，风化层/土壤的形成是由热空间风化引起的持续过程，即使在无空气、无水和低重力环境中，这也是一种有效的侵蚀手段。最后，由无定形冰的结晶引起的彗星物质的升华产生了大的水力裂缝。这些裂缝的传播将加压的蒸气-尘埃乳状液输送到彗星核的表面，导致灾难性的蒸气-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.