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

每天大约有100吨地外物质进入地球大气层，主要由流星体组成。流星体被定义为太空中自然起源的固体粒子，通常起源于彗星和小行星的解体，并根据其来源进行分类。平均每天有超过1000亿颗质量大于1微克的流星体进入地球大气层。如果在太阳轨道上，流星体相对于地球的运行速度在11到72.8公里/S之间；一小部分流星体起源于我们的太阳系之外，这意味着遥远的恒星系统可能会影响地球环境。与流星体通过行星大气层有关的光和相关的物理现象被称为流星，它是流星体沿其轨道电离气体时产生的等离子体的结果。虽然流星体对我们的空间环境有深远的影响，但我们对它们的基本性质知之甚少。由于缺乏关于背景属性如何影响等离子体动力学以及观测仪器的选择效应如何影响探测的知识，流星体属性和等离子体形成之间的联系仍然知之甚少。这个项目试图通过探索围绕流星体的等离子体物理，即所谓的头部回声等离子体来回答这些问题，并揭示流星体属性、等离子体形成和背景电离层属性之间的联系。这项研究将解决流星和流星体群落中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，主要密度人口，以及背景电场和磁场对等离子体膨胀和分布的影响。这项基础性研究包括三个模拟的发展，包括用于确定等离子体形成和扩展的直接模拟蒙特卡罗(DSMC)模型和粒子在单元(PIC)算法，以及用于将雷达信号强度与等离子体密度关联的时域有限差分(FDTD)模型。项目组还将收集和分析不同地理位置的高功率大口径(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性演变的目标，并回答以下三个科学问题：1)流星等离子体的性质，包括峰值等离子体密度和分布；2)流星体消融和等离子体形成是如何受到高层大气和电离层物理影响的？3)母流星体的性质，包括质量、体积密度和速度，以及它们与流星等离子体的关系？这项研究的结果将使人们能够理解撞击等离子体，并促进麻省理工学院海斯塔克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，还将广泛传播人类解放军的数据，以增进对科学和技术的了解。研究生将参与建模和仿真的方方面面，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。这项研究将被整合到斯坦福大学的课堂上，包括由PI设计和教授的三个研究生班和一个本科生班。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、本科生火星任务计划以及各种电视节目，如国家地理、天气频道和PBS Nova，在这些节目中，她描述了流星体如何威胁星际空间项目。这些努力将激励斯坦福大学以外的新一代学生攻读这一研究领域的学位。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.