CSEDI Collaborative Research: Understanding of the effects of large planetesimal collisions on Hadean Earth mantle dynamics

CSEDI合作研究：了解大型星子碰撞对冥古宙地幔动力学的影响

• 批准号: 2102777
• 负责人: Jun Korenaga
• 金额: $ 33.91万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2102777&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Understanding; effects

The evolution of the Hadean Earth (4-4.5 billion years ago) was shaped by large-scale interplanetary collisions, characterized by impactors with diameters ranging from 1,000 to 4,000 km. The defining characteristics of the Earth, such as oceans, continents, life, and plate tectonics are likely to have appeared for the first time on the Hadean eon. It thus seems inevitable that their emergence would have been affected by these early collisions, though to what extent they were affected remains an open question. In particular, little understood are the effects of these collisions on the internal evolution of the Earth. Collisions are thought to have contributed significantly to the abundance of highly iron-loving elements (e.g., Au, Ir, Ru) in the Earth’s mantle, but the details of their delivery through impacts are not fully understood due to complex mixing processes that arise when a projectile collides with the early Earth. In addition, it is not well-understood how the long-term evolution of the Earth’s mantle could have responded to the injection of materials derived from the impactors. This project introduces an innovative computational approach that combines impact simulations with models that explore the long-term evolution of the Earth’s interior to quantify the delivery of highly iron-loving elements, their distribution in the mantle, and the total mass of late accreted materials. These results allow for an increased understanding of the Hadean Earth surface environment. Moreover, the connections between short-term impact dynamics and long-term mantle dynamics may shed light on the origin of anomalies in the mantle (such as the large low-shear-velocity provinces, which are the most significant anomalies on the deep mantle), the dynamics of mantle plumes, and the history of the geomagnetic field. This project also provides support for interdisciplinary training of a graduate student, an undergraduate internship where the Southwest Research Institute will host 1-2 geophysics major from Yale University, and a series of movies that visualize planetesimal impacts and mantle dynamics for education outreach.The geophysical evolution of Hadean Earth was controlled by large-scale collisions and mantle dynamics, but the interplay of these processes remains largely unexplored. The Earth’s protracted bombardment of leftover planetesimals after the Moon-forming giant impact, called “late accretion”, is supported by the lunar cratering record and is required to explain the abundance of as well as the chondritic proportions of highly siderophile elements (HSEs) in the present-day mantle. Recently, based on impact simulations with smooth-particle hydrodynamics (SPH), the late accreted mass has been suggested to be two to five times higher than previously thought, because the metallic cores of large differentiated planetesimals, where the bulk of HSEs reside, are not efficiently mixed into the mantle. Such an upward revision of late accreted mass could dramatically modify our understanding of the Hadean Earth. This suggestion based on SPH simulations is, however, still provisional because important complications arising from long-term mantle dynamics are not incorporated. Thus, the delivery of HSEs, their distribution in the mantle, and the total mass of the late accretion are still wide-open questions, with important consequences on the Hadean Earth surface environment. This project aims to achieve the following two major objectives: (1) to quantify the fate of differentiated planetesimal cores during impacts, by re-evaluating SPH simulations including the physics of fragmentation, and (2) to understand the long-term fate of fragmented metallic blobs by conducting systematic mantle mixing simulations. The primary goal of this project is to determine the absolute scale of planetesimal impact history, but achieving this goal will also help to address a wide range of important questions, from the habitability of the early Earth to the origin of deep geochemical reservoirs.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.

冥古宙地球（40 - 45亿年前）的演变是由大规模的行星际碰撞形成的，其特征是直径从1 000公里到4 000公里不等的撞击物。地球的定义性特征，如海洋、大陆、生命和板块构造，很可能是在冥古宙第一次出现。因此，它们的出现似乎不可避免地会受到这些早期碰撞的影响，尽管它们受到多大程度的影响仍然是一个悬而未决的问题。特别是，人们对这些碰撞对地球内部演化的影响知之甚少。 碰撞被认为对富含高度亲铁元素（例如，Au、Ir、Ru），但由于抛射体与早期地球碰撞时产生的复杂混合过程，它们通过撞击传递的细节尚未完全了解。此外，人们还不太清楚地幔的长期演化如何对来自撞击物的物质注入作出反应。该项目引入了一种创新的计算方法，将撞击模拟与探索地球内部长期演化的模型相结合，以量化高度亲铁元素的交付，它们在地幔中的分布以及后期增生物质的总质量。这些结果可以增加对冥古宙地球表面环境的了解。此外，短期冲击动力学和长期地幔动力学之间的联系可能揭示地幔异常的起源（如大的低剪切速度区，这是最重要的地幔深部异常），地幔柱的动力学，以及地磁场的历史。该项目还为研究生的跨学科培训提供支持，西南研究院将接待1-2名耶鲁大学物理学专业的本科生实习，以及一系列可视化微行星撞击和地幔动力学的电影用于教育推广。Hadean地球的地球物理演化受到大规模碰撞和地幔动力学的控制，但这些过程的相互作用在很大程度上仍未得到探索。地球在形成月球的巨大撞击后对剩余星子的长期轰击，称为“后期吸积”，得到了月球陨石坑记录的支持，并需要解释现今地幔中高度亲铁元素（HSE）的丰度和比例。最近，基于光滑粒子流体动力学（SPH）的碰撞模拟，晚期吸积质量被认为比以前认为的高出2到5倍，因为大部分HSE居住的大型分化微行星的金属核心没有有效地混入地幔。这种对晚期吸积质量的向上修正可能会极大地改变我们对冥古宙地球的理解。然而，基于SPH模拟的这一建议仍然是临时的，因为没有考虑长期地幔动力学产生的重要复杂情况。因此，交付的HSEs，它们在地幔中的分布，以及后期吸积的总质量仍然是一个悬而未决的问题，对冥古宙地球表面环境的重要后果。该项目旨在实现以下两个主要目标：（1）通过重新评估SPH模拟，包括碎裂物理学，量化撞击期间分化的星子核的命运，以及（2）通过进行系统的地幔混合模拟，了解碎裂金属团块的长期命运。该项目的主要目标是确定小行星撞击历史的绝对规模，但实现这一目标也将有助于解决广泛的重要问题，从早期地球的可居住性到深层地球化学水库的起源。该奖项反映了NSF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。