Characterization of Meteoroids and Meteors through Simulations and Remote Sensing Using High-Power Large-Aperture Radars

每天大约有100吨主要由流星体组成的地外物质进入地球大气层。流星体被定义为太空中自然形成的固体颗粒，通常来自彗星和小行星的分裂，并根据它们的起源进行分类。平均每天有超过1000亿个质量大于1微克的流星体进入地球大气层。流星体在太阳轨道上相对于地球的速度在11到72.8公里/秒之间；一小部分（虽然尚未确定）来自太阳系之外，这意味着遥远的恒星系统可以影响地球的环境。流星体穿过行星大气层时产生的光和相关的物理现象被称为流星，这是流星体在电离其轨道上的气体时产生的等离子体造成的。虽然流星体对我们的空间环境有着深远的影响，但我们对它们的基本特性知之甚少。流星体性质与等离子体形成之间的联系仍然知之甚少，因为缺乏关于背景性质如何影响等离子体动力学以及观测仪器中的选择效应如何影响探测的知识。这个项目试图通过探索流星体周围的等离子体物理来回答这些问题，被称为头部回波等离子体，并揭示流星体特性、等离子体形成和背景电离层特性之间的联系。这项研究将解决流星和流星体界的许多悬而未决的问题，包括进入我们大气层的质量沉积速率，优势密度种群，以及背景电场和磁场对等离子体膨胀和分布的影响。这项基础研究包括三个模拟的发展，包括直接模拟蒙特卡罗（DSMC）模型和粒子胞内（PIC）算法，用于确定等离子体的形成和膨胀，以及有限差分时域（FDTD）模型，用于将雷达信号强度与等离子体密度关联起来。项目团队还将收集和分析不同地理位置的高功率、大孔径（HPLA）雷达数据。这项研究将有助于国家空间天气计划了解电离层不规则演变的目标，并回答以下三个科学问题：1)流星等离子体的特性是什么，包括峰值等离子体密度和分布？2)上层大气和电离层的物理特性如何影响流星体的消融和等离子体的形成？3)母流星体的性质是什么，包括质量、体积密度和速度，它们与流星等离子体有什么关系？这项研究的结果将有助于理解撞击等离子体，并促进麻省理工学院干草堆天文台和斯坦福大学之间的合作。除了开发的模型和模拟外，HPLA数据将广泛传播，以增进科学和技术的了解。研究生将参与建模和仿真的各个方面，本科生和研究生都将能够分析HPLA数据，这将有助于培养下一代科学家和工程师。该研究将整合到斯坦福大学的课堂中，包括由PI设计和教授的三个研究生班和一个本科班。除了开发和教授这些课程外，PI还经常参与外展活动，例如与小学合作，为本科生提供火星任务计划，以及各种电视节目，例如国家地理，天气频道和PBS NOVA，她在其中描述了流星体如何威胁行星际空间计划。这些努力将激励斯坦福大学直接从事这一研究领域的下一代学生攻读学位。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Approximate 100 tons of extraterrestrial matter, primarily composed of meteoroids, enters the Earth’s atmosphere every day. Meteoroids are defined as solid particles of natural origin in space, which typically originate from the breakup of comets and asteroids and are categorized according to their origin. On average, over 100 billion meteoroids enter Earth’s atmosphere daily with masses larger than 1 microgram. Meteoroids travel between 11 and 72.8 km/s relative to the Earth if in solar orbit; a small, though as yet undetermined, fraction originates outside of our solar system, implying that distant stellar systems can impact Earth’s environment. The light and associated physical phenomena associated with a meteoroid’s passage through a planet’s atmosphere is called a meteor, which results from the plasma created by the meteoroid as it ionizes the gas along its trajectory. Although meteoroids have a profound effect on our space environment, we know very little about their fundamental properties. The connection between meteoroid properties and plasma formation still remains poorly understood due to a lack of knowledge regarding how background properties influence the plasma dynamics and also how selection effects in the observing instrument impacts detection. This project seeks to answer these questions by probing into the plasma physics that surrounds the meteoroid, known as the head echo plasma, and uncover the connection between meteoroid properties, plasma formation, and the properties of the background ionosphere. The research will address many of the outstanding questions in the meteor and meteoroid community, including the mass deposition rate into our atmosphere, the dominant density population, and the effect of the background electric and magnetic fields on plasma expansion and distribution. This fundamental research includes the development of three simulations, including a Direct Simulation Monte Carlo (DSMC) model and a Particle-In-Cell (PIC) algorithm to determine the plasma formation and expansion, and a Finite-Difference Time-Domain (FDTD) model to correlate radar signal strength with plasma density. The project team will also collect and analyze High-Power, Large-Aperture (HPLA) radar data at diverse geographic locations. This research will contribute to the National Space Weather Program’s goal of understanding the evolution of ionospheric irregularities, and answer the following three scientific questions:1) What are the properties of meteor plasmas, including peak plasma density and distribution?2) How is meteoroid ablation and plasma formation affected by the physics of the upper atmosphere and ionosphere?3) What are the properties of the parent meteoroids, including mass, bulk density, and velocity, and how do they correlate to the meteor plasmas?The results of this research will enable understanding of impact plasma and facilitate collaboration between MIT Haystack Observatory and Stanford University. The HPLA data, in addition to the models and simulations developed, will be widely disseminated to enhance scientific and technological understanding. Graduate students will be involved in all aspects of the modeling and simulation, and both undergraduate and graduate student students will be able to analyze the HPLA data, which will contribute to the training of the next generation of scientists and engineers. The research will be integrated into the classroom at Stanford University, including three graduate classes and one undergraduate class designed and taught by the PI. In addition to developing and teaching these courses, the PI frequently engages in outreach activities, such as with grade schools, the Mission to Mars Program for undergraduate students, and various television programs, such as National Geographic, the Weather Channel, and PBS NOVA, where she has described how meteoroids can threaten interplanetary space programs. These endeavors will inspire another generation of students beyond those directly engaged at Stanford University to pursue a degree in this field of research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.