Binary Near-Earth Asteroid Formation from Rotational Disruption of Gravitational Aggregates

AST 0708110 Richardson Dr.马里兰州大学的Derek Richardson将开展一项旨在了解近地小行星双星的起源和演变的研究方案。在以前的NSF资助的工作中，研究小组根据脆弱小行星与地球在广泛的遭遇参数范围内的潮汐遭遇建立了二元NEA形成效率。他们确定，以这种方式形成的双星的稳态数量最多为近地小行星总数的2%，而观测到的是15%。这是动机，以确定是否需要改进的模型或一个新的模型（如热致自旋），以充分解释观察。将进行四项任务：1）模拟双星的长期综合，包括研究组件形状效应、潮汐演变和实际近地天体轨道的影响，以提高稳态模型的复杂性; 2）研究颗粒大小/形状和聚集体强度对旋转破裂后双星形成的影响，以评估哪些方面促进和抑制双星形成; 3）结合任务1和2的结果确定双星形成的效率; 4）维护和传播观测和模拟的公共数据库。研究小组开发了一种工具，可以根据其他模拟的输入，快速预测二进制的稳态种群，包括从主带迁移进来的预先存在的二进制。当执行新的模拟时，结果很容易并入预测算法中。 这提供了一种强有力的方法来测试无数物理效应对双星产生和进化的相对重要性。没有其他小组拥有重力和碰撞的高性能模拟工具与可以解决拟议研究的分析方法相结合。鉴于观测工作的迅速改进以及最近和即将进行的航天器飞行任务提供的新数据，这一理论研究是了解太阳系小天体性质和演变的一个重要组成部分，研究结果有助于深入了解近地小行星的内部结构，并对减灾战略产生影响。如果不是所有近地小行星双星的性质都与旋转破裂的起源相一致（到目前为止，至少有一些可以用这种方式解释），那么就可以确定近地小行星通常必须具有非常低的拉伸强度。总的来说，特别是对近地小行星的更好了解将导致对小行星的更好了解，从而将有助于深入了解行星组成部分的形成和演变。如果近地小行星确实是由重新聚集的碎片组成的脆弱集合体，那么减轻此类天体与地球碰撞危险的战略将受到影响，而且现在已知约有15%的近地小行星是双星，这种影响将加倍。因此，这项研究的意义不仅仅是理解二元NEAs的起源。作为推广的一部分，观测到的二元小天体的公共储存库将与教育资源一起沿着，不仅解释外行和学生层面的研究，而且解释小天体的相关方面。这些数据将不断更新，并每年提交给NASA行星数据系统。 在工作期间，至少有一名新的研究生将加入团队。该研究还将建立和加强西南研究所（通过合作者Bottke），密歇根大学（通过合作者Scheeres）和马里兰州大学之间的伙伴关系。

AST 0708110RichardsonDr. Derek Richardson, University of Maryland, will carry out a research program aimed at understanding the origin and evolution of binary near-Earth asteroids (NEAs). In previous NSF funded work, the research team established the binary NEA formation efficiency based on tidal encounters of fragile asteroids with Earth over a wide range of encounter parameters. They established that the steady-state number of binaries formed in this way is at most 2% of the total number of NEAs, compared to the observed 15%. This is motivation to determine whether improvements to the model or a new model entirely (such as thermally induced spin-up) is required to fully explain the observations. Four tasks will be carried out: 1) long-term integration of simulated binaries, including study of component shape effects, tidal evolution, and effect of realistic NEA orbits, to improve the sophistication of the steady-state model; 2) investigation of the effect of particle size/shape and aggregate strength on binary formation following rotational disruption, to assess which aspects enhance and which suppress binary formation; 3) determination of the efficiency of binary formation, incorporating results from Tasks 1 and 2; and 4) maintenance and dissemination of a public database of observations and simulations. The research team has developed a tool that quickly provides predictions of steady-state populations of binaries, including pre-existing binaries migrating in from the Main Belt, on the basis of inputs from other simulations. As new simulations are performed, the results are easily incorporated into the predictive algorithm. This provides a powerful way of testing the relative importance of a myriad of physical effects on binary production and evolution. No other group possesses the combination of high-performance simulation tools for gravity and collisions with analysis methods that can address the proposed research. In light of rapidly improving observations and new data from recent and forthcoming spacecraft missions, this theoretical study is an important component of understanding the nature and evolution of small bodies in the solar system.Results from this research are giving insight into the internal structure of NEAs and have implications for hazard mitigation strategies. If the properties of most if not all NEA binaries are consistent with a rotational disruption origin (so far at least some can be accounted for in this way), it will be established that NEAs in general must have very low tensile strength. Overall, a better understanding of NEAs in particular will lead to a better understanding of asteroids in general, and will therefore give insight into the formation and evolution of the building blocks of planets. If NEAs are indeed fragile assemblages of reaccumulated fragments, strategies for mitigating the hazard of such bodies colliding with Earth will be affected, and doubly so now that about 15% of NEAs are known to be binaries. Thus, this study has implications beyond just understanding the origin of binary NEAs. As an outreach component, a public repository of observed binary small bodies will be maintained along with educational resources to explain not only the research at the layman and student levels but also related aspects of small bodies in. The data will be updated on an ongoing basis and submitted to the NASA Planetary Data System annually. At least one new graduate student will join the team over the work period. The research will also build and strengthen partnerships between the Southwest Research Institute (through collaborator Bottke), University of Michigan (through collaborator Scheeres), and the University of Maryland.***