Origin of Binary Near-Earth Asteroids

AST 0307549理查森博士马里兰大学的德里克·理查森将开展研究，旨在了解双星近地小行星(NEA)的起源。目前来自光曲线分析和雷达成像的估计表明，至少15%的近地小行星(在0.017 AU范围内接近地球的小行星)可能是双星，即由两颗围绕共同质心运行的小行星组成的动力系统。此外，大约50%的快速旋转的近地天体(自转周期在2至4小时之间)的直径超过0.2公里，似乎是双星。NEA双星与其他观测到的小行星双星群体，即主带、特洛伊和柯伊伯带双星似乎有本质上的不同。特别是，NEA二进制文件往往具有较小的间隔和组件之间的中等大小比率。如果潮汐扰动在双星近地天体的形成中发挥了重要作用，那么这些特征以及在类地行星上形成双星陨石坑的频率可以得到解释。然而，为了有效地进行潮汐破坏，前身必须是脆弱的(重力集合体或碎石堆)，因此能够被潮汐撕裂。越来越多的观测证据表明，这样的天体存在：彗星解体、陨石坑链、双星陨石坑、截断自转、低体积密度、巨大的陨石坑、表面凹槽和不寻常的形状，这些都是彗星和小行星之间脆弱的、可能是碎石结构的迹象。然而，以前关于类地行星对小行星的潮汐破坏的研究要么是非常简化的模型，要么主要关注于区分严重和轻微的破坏，而没有特别集中于双星形成。理查森博士将对地球对近地天体的潮汐破坏进行高分辨率的数值模拟，以确定双星形成的频率和由此产生的双星系统的典型特征。要采样的参数空间包括前体大小、形状、旋转、相遇速度和近距离。第一年的工作将包括一些软件开发，因为虽然主要的模拟软件已经编写并稳定，但需要针对拟议项目的辅助代码来实现自动化和分析。在第二年和第三年，将主要进行参数空间的探索。这项研究的结果将与现有和未来对双星近地天体的观测结果进行比较，以确定潮汐破坏是否可以解释部分或全部现有人口。将在更长的时间间隔内进行一些模拟，以将演变与分析估计进行比较，特别是推导出碎石堆的潮汐耗散参数Q，该参数可用于估计双星系统的长期演变，而不需要显式积分。这些模拟还将检查缓慢或翻滚的旋转体，以努力了解这种异常旋转状态是如何产生的。这项研究的结果将使人们深入了解近地生态系统的内部结构，并可能对减灾战略产生影响。总体而言，尤其是更好地了解近地小行星，将有助于更好地了解小行星的一般情况，从而更清楚地了解我们的起源。这项工作的一部分需要开发一个基于网络的界面，用于组织和挖掘将产生的大量数据集。一名有网页设计经验的本科生将帮助这一发展。事实上，多达三名本科生和两名研究生将直接参与这个项目。一旦项目完成，网络界面将向公众开放，供公众自由访问我们的数据。*

AST 0307549RichardsonDr. Derek Richardson, University of Maryland, will carry out research aimed at understanding the origin of binary near-Earth asteroids (NEAs). Current estimates from light curve analysis and radar imaging suggest that at least 15% of NEAs (asteroids that approach Earth within 0.017 AU) may be binaries, i.e., dynamical systems that consist of two asteroids orbiting a common center of mass. Moreover, roughly 50% of fast-spinning NEAs (having rotation periods between 2 and 4 hours) with diameters larger than 0.2 km appear to be binaries. The NEA binaries appear qualitatively different from other observed asteroid binary populations, namely the main belt, Trojan, and Kuiper belt binaries. In particular, the NEA binaries tend to have small separations and intermediate size ratios between components. These characteristics, and the frequency of doublet crater formation onterrestrial planets, may be explained if tidal disruption plays an important role in the creation of binary NEAs. However, for tidal disruption to be effective, the progenitor must be fragile (a gravitational aggregate or rubble pile) and therefore capable of being pulled apart by tides. Observational evidence has been mounting that such bodies exist: comet breakups, crater chains, doublet craters, truncated spins, low bulk densities, giant craters, surface grooves, and unusual shapes are all indications of weak, possibly rubble structure among comets and asteroids. Yet previous studies of tidal disruption of asteroids by terrestrial planets were either very simplified models or were concerned primarily with distinguishing between severe and mild disruption without specifically concentrating on binary formation. Dr. Richardson will perform high-resolution numerical simulations of the tidal disruption of NEAs by the Earth to determine the frequency of binary formation and the typical characteristics of the resulting binary systems. The parameter space to be sampled includes progenitor size, shape, spin, encounter speed, and close-approach distance. The first year of the effort will include some software development since, although the main simulation software is already written and stable, auxiliary codes specific to the proposed project are needed for automation and analysis. In the second and third years the main exploration of parameter space will take place. The results of this study will be compared to existing and future observations of binary NEAs to establish whether tidal disruption can explain some or all of the existing population. Some simulations will be carried out for a longer interval to compare the evolution with analytical estimates, in particular to derive the tidal dissipation parameter Q for a rubble pile, a quantity that could be used to estimate the long-term evolution of a binary system without requiring explicit integration. The simulations will also be examined for slow or tumbling rotators in an effort to understand how such anomalous rotation states originate. Results from this research will give insight into the internal structure of NEAs and may have implications for hazard mitigation strategies. Overall, a better understanding of NEAs in particular will lead to a better understanding of asteroids in general, and thereby to a clearer picture of our origins.Part of this work entails the development of a web-based interface for organizing and mining thelarge data sets that will be produced. An undergraduate student with experience in web design will assist in this development. In fact, as many as three undergraduate students and two graduate students will be involved directly in this project. Once the project is completed, the web interface will be available to the public for accessing our data freely.***