Observational Study of the Rotation Rates of Very Small Near-Earth Asteroids

AST-0908868 Eileen Ryan该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该项目的动机是我们对目前发现的最小近地小行星（NEAs）的物理特性缺乏了解。 对于自转周期来说尤其如此，它可以提供有关小行星内部成分，断裂程度和碰撞历史的信息。 目前的数据表明，直径小于200米的近地小行星的自转速度超过2.2小时，这是理论上推导出的无强度椭球体的临界自转极限，而较大的天体自转速度较慢。 这表明，这些快速旋转的小物体是固体，因此很可能是曾经组成碎石堆母体的单个碎片，这些碎片被灾难性的撞击破坏了。 然而，已知自转周期的小行星的样本量很小，需要更可靠的统计样本。 马格达莱纳海岭天文台最先进的2.4米望远镜将用于确定每年15-20个小近地小行星的自转周期（通过光变曲线）和物质分类（通过分光光度法）。 到这个为期三年的项目结束时，具有特征的小近地小行星的数目预计将增加一倍以上，如果如初步研究者的初步观察所表明的那样，存在着很大比例的缓慢旋转的小天体，那么在低质量一端很可能常见“碎石堆”（相对于整体或连贯天体）。 这一结果对于评估和规划这些物体构成的威胁十分重要。 该项目将在一个为少数民族服务的机构开展，并为这些学生提供研究和培训经验（尽管这里不包括直接支助）。 研究人员将把近地小行星观测和这项研究所涉及的概念作为K-12教育工作者科学教学硕士课程的一部分，他们经常就这些主题进行公开演讲。

AST-0908868Eileen RyanThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project is motivated by our lack of knowledge of the physical properties of the very smallest Near-Earth Asteroids (NEAs) now being discovered. This is particularly true for rotation periods, which can provide information about an asteroid's internal composition, degree of fracture, and collisional history. Current data suggest that NEAs smaller than 200 meters in diameter rotate faster than 2.2 hours, which is the theoretically derived critical rotation limit for strengthless ellipsoids, while larger bodies rotate more slowly. This suggests that the small fast rotating objects are solid and so are likely to be individual fragments that once made up a rubble pile parent body that was disrupted by a catastrophic impact. However, the sample size of small asteroids with known rotation periods is small and a more robust statistical sample is needed. The state-of-the-art 2.4-meter telescope at the Magdalena Ridge Observatory will be used to determine rotation periods (through light curves) and material classifications (through spectrophotometry) for 15-20 small NEAs per year. By the end of the three year project, the number of characterized small NEAs is expected to have more than doubled.If, as suggested by preliminary observations by the PIs, a large percentage of slowly rotating small bodies exists, it may well be the case that "rubble piles" (versus monolithic or coherent bodies) are common at the low-mass end. Such a result is important in assessing and planning for the threat posed by these objects. The project will be carried out at a minority serving institution and provide research and training experiences for these students (though no direct support is included here). The researchers will include Near-Earth Asteroid observations and the concepts involved in this research as part of a Masters of Science Teaching program for K-12 educators, and they routinely give public talks on these topics.