The 4.1-billion-year-old meteorite Allan Hills 84001 (ALH 84001) may preserve a magnetic record of the extinct martian dynamo. However, previous paleomagnetic studies have reported heterogeneous, nonunidirectional magnetization in the meteorite at submillimeter scales, calling into question whether it records a dynamo field. We use the quantum diamond microscope to analyze igneous Fe-sulfides in ALH 84001 that may carry remanence as old as 4.1 billion years (Ga). We find that individual, 100-μm-scale ferromagnetic mineral assemblages are strongly magnetized in two nearly antipodal directions. This suggests that the meteorite recorded strong fields following impact heating at 4.1 to 3.95 Ga, after which at least one further impact heterogeneously remagnetized the meteorite in a nearly antipodal local field. These observations are most simply explained by a reversing martian dynamo that was active until 3.9 Ga, thereby implying a late cessation for the martian dynamo and potentially documenting reversing behavior in a nonterrestrial planetary dynamo.

中文翻译：

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古地磁证据表明存在约 3.9 Ga 的长寿且可能反转的火星发电机


41 亿年前的陨石 Allan Hills 84001 (ALH 84001) 可能保存着已灭绝的火星发电机的磁记录。然而，之前的古地磁研究报告称，陨石中存在亚毫米级的异质、非单向磁化，令人质疑它是否记录了发电机场。我们使用量子金刚石显微镜分析 ALH 84001 中的火成铁硫化物，其剩磁可能长达 41 亿年 (Ga)。我们发现单个 100 微米级的铁磁矿物组合在两个几乎相反的方向上被强烈磁化。这表明陨石在 4.1 至 3.95 Ga 的撞击加热后记录了强磁场，此后至少一次进一步的撞击使陨石在几乎相反的局部磁场中非均匀地重新磁化。这些观察结果最简单地可以通过一个活跃到 3.9 Ga 的火星发电机反转来解释，从而意味着火星发电机的晚期停止，并可能记录非地球行星发电机的反转行为。