Magnetic Field Investigations of Mars and Mercury

拟议的研究计划旨在了解水星和火星的磁场环境。在水星和火星，磁场来自“内部来源”，如金属核心中的流体运动和/或地壳岩石的磁化，以及“外部来源”，如在行星表面高处产生的电流系统。由此产生的环境提供了关于每颗行星的内部、其演化及其与太阳风(从太阳向外流出的带电粒子流)相互作用的基本线索。过去和现在与太阳风的相互作用具有重要的后果。例如，火星上地表水的非凡历史在一定程度上与地球大气抵御太阳风侵蚀的能力有关。相反，在水星上，直接轰击表面是可能的，但还没有完全量化。这一过程可以改变表面(空间风化)，并弹出原子和分子形成稀薄的大气(外圈)。最后，外部磁场的时间变化(例如，由太阳风驱动)可以在行星内部产生电流，从而产生二次磁场。这种场是研究内部电导结构的独特探头。 我们将使用信使号任务(2011-2015)的轨道数据来研究水星内部磁场的性质和历史。我们将描述内部核心领域，以提供对最先进的发电机模型的关键约束。对地壳磁场的研究将阐明地壳中磁化的分布和来源以及发电机的历史。最后，这项拟议的工作还将识别和理解外部场环境中的时间变化，并确定这些动力学如何与水星内部耦合。 对火星的研究将使用火星全球勘测者(1997-2006)和MAVEN(2014-现在)任务返回的卫星观测，以及洞察力任务(2016年及以后)对火星磁场的首次地表测量。我们的工作将表征外部磁场，探测地壳和地幔的电导结构，并为地壳磁场提供改进的模型。这将有助于了解电离层(最上层大气层)的结构和来源，并限制地壳和地幔中未知和有争议的挥发性成分。 拟议中的磁场研究是研究重要物理过程的关键、实用方法，这些物理过程支配着我们自己以及其他太阳系中行星的进化和宜居性。获得资助的人员将为国际行星飞行任务作出贡献，并接受行星物理、计算和数据分析方面的高水平培训，为他们在学术界、政府或私营行业的广泛机会做好准备。

The proposed research program aims to understand the magnetic field environments of Mercury and Mars. At Mercury and Mars, magnetic fields arise from “internal sources” such as fluid motions in the metallic core and/or magnetization of crustal rocks, and from “external sources” such as current systems generated high above the planet’s surface. The resulting environments provide fundamental clues about each planet’s interior, its evolution and its interaction with the solar wind (the stream of charged particles that flows outward from the sun). Past and present interactions with the solar wind have important consequences. For example, the remarkable history of surface water on Mars is tied partly to the resilience of the planet’s atmosphere against erosion by the solar wind. In contrast, on Mercury, direct bombardment of the surface is possible but not yet fully quantified. This process can modify the surface (space weathering), and eject atoms and molecules to form a tenuous atmosphere (exosphere). Finally, time-variations in external magnetic fields (e.g., driven by the solar wind) can generate electrical currents in the planetary interior that produce secondary magnetic fields. Such fields are a unique probe of interior electrical conductivity structure. We will investigate the nature and history of Mercury’s internal magnetic field using orbital data from the MESSENGER mission (2011-2015). We will characterize the internal core field to provide critical constraints on state-of-the-art dynamo models. Investigations of crustal magnetic fields will elucidate the distribution and origin of magnetization in the crust and the history of the dynamo. Finally, the proposed work will also identify and understand time-variations in the external field environment and determine how these dynamics couple to Mercury’s interior. Studies of Mars will use satellite observations returned by the Mars Global Surveyor (1997-2006) and MAVEN (2014 - present) missions, as well as the first-ever surface measurements of Mars’ magnetic field from the InSight mission (2016 onwards). Our work will characterize external magnetic fields, probe the electrical conductivity structure of the crust and mantle, and provide improved models for the crustal magnetic field. It will contribute to understanding the structure and origin of the ionosphere (uppermost atmosphere) as well as to constraining the unknown and contentious volatile content of the crust and mantle. The proposed magnetic field studies are a key, practical approach to investigating important physical processes that govern the evolution and habitability of planets in our own, and other solar systems. Funded personnel will contribute to international planetary missions and receive high-level training in planetary physics, computing and data analysis preparing them for a broad range of opportunities in academia, government or private industry.