Observational studies of small solar system bodies: origins, dynamics and structure

太阳系中的小天体（小行星、彗星、半人马和海王星外天体）是我们太阳系形成阶段的遗迹。在许多情况下，它们含有未经实质性加工的原始材料。它们的物理结构、化学和动态演化为我们了解太阳系和其他行星系统的早期形成模型提供了一个独特的窗口。这些天体的碎片偶尔会撞击地球大气层，以“流星”的形式产生电离、辐射和冲击。通过研究碎片（流星体）如何在大气中消融，我们可以重建它的特性（体积密度、强度、粒度），进而了解它的母体。这个提议的方法是通过记录它们的光、电离和激波产生来观察从尘埃颗粒到巨石的大小不等的流星体与大气的相互作用。通过测量它们的质量和各种大小的数量，我将准确地估计这些天体到地球的通量。对于较小的流星体，这将有助于提炼地球积累的陨石物质的数量。对于较大的物体（米-十米尺度），我将测量它们的冲击效果，特别是冲击强度，因为这对于限制火球如何在地面上造成损害至关重要。2015年2月15日，俄罗斯车里雅宾斯克发生了空中爆炸事件，因此迫切需要更好的地面破坏模型，以便在另一个几米大小的近地物体在撞击前被探测到时，帮助民防官员了解情况。对于这些较大的事件，陨石的恢复也为前体的组成和结构提供了“基础真相”。如果我们能够同时记录大气中的火球，那么这种较大的撞击物也会形成进入模型的最终校准。通过模拟各种尺寸的大气中的解体行为，我将测量大量流星体的强度和体积密度，并将其与撞击前的轨道相关联。结果将是一幅详细的协调图像，显示尘埃到巨石大小的物体与地球相撞的强度/结构和轨道起源。最终，这将从尘埃和较大的近地天体（NEOs）的角度，建立起一幅近地空间小天体的起源和当前生态的图景。由此得出的地球附近从尘埃到巨石大小的流星体的数量和物理特征的“路线图”，对于行星防御和保护航天器免受流星体撞击具有实际重要性。这些信息也需要用于即将到来的航天器任务，比如NASA的小行星重定向任务，该任务旨在将一块巨石大小的岩石从一颗近地小行星带回月球轨道

The small bodies in the solar system (asteroids, comets, centaurs and trans-Neptunian objects) are relics from the formation stage of our solar system. In many cases they contain primitive material which has not experienced substantial processing. Their physical structure, chemistry and dynamical evolution offer a unique window into the early solar system informing formation models of our solar system and other planetary systems.***Fragments of these bodies occasionally impact the Earth's atmosphere, producing ionization, radiation and shocks in the form of “meteors”. By studying how the fragment (meteoroid) ablates in the atmosphere we can reconstruct its properties (bulk density, strength, grain sizes) and by extension learn about its parent body.***The approach of this proposal is to observe meteoroids ranging in size from dust grains to boulders interacting with the atmosphere by recording their light, ionization and shock production. By measuring their mass and numbers at all sizes I will accurately estimate the flux of these bodies to Earth. For smaller meteoroids this will help in refining the amount of meteoritic material accumulated by the Earth. For larger objects (meter-decameter-scale) I will measure their impact effects, particularly shock strength, as this is critical to constraining how fireballs can cause damage at the ground. In the wake of the Feb 15, 2015 Chelyabinsk airburst over Russia there is a pressing need for better ground damage models to help inform civil defence officials in the event another multi-meter sized near-Earth object is detected just prior to impact. For these larger events, recovery of meteorites also provides “ground-truth” for precursor body composition and structure. Such larger impactors also form the ultimate calibration for entry models, if we are able to simultaneously document the fireball in the atmosphere. Through modelling of the breakup behavior in the atmosphere at all sizes I will measure the strength and bulk density of a large number of meteoroids and correlate this with their pre-impact orbits. The result will be a detailed coordinated picture of the strength/structure and orbital origins for dust-to-boulder sized objects colliding with the Earth. Ultimately this will build up a picture of the origins and present ecology of small bodies in near-Earth space both in terms of dust and larger Near-Earth Objects (NEOs). The resulting “road-map” of the number and physical characteristics of dust to boulder sized meteoroids near Earth is of practical importance for planetary defence and for the protection of spacecraft from meteoroid impacts. This information is also needed for upcoming spacecraft missions such as the NASA Asteroid Redirect Mission, which seeks to return a boulder-sized rock to lunar orbit from a near-Earth asteroid.**