Palaeomagnetic studies of Apollo samples indicate that the Moon generated a magnetic field for at least 2 billion years^1,2. However, the geometry of the lunar magnetic field is still largely unknown because the original orientations of essentially all Apollo samples have not been well constrained. Determining the direction of the lunar magnetic field over time could elucidate the mechanism by which the lunar dynamo was powered and whether the Moon experienced true polar wander. Here we present measurements of the lunar magnetic field 3.7 billion years ago as recorded by Apollo 17 mare basalts 75035 and 75055. We find that 75035 and 75055 record a mean palaeointensity of ~50 μT. Furthermore, we could infer from the magnetization direction of 75055 and the layering of its parent boulder that the inclination of the magnetic field at the time was 34 ± 10°. Our recovered inclination is consistent with, but does not require, a selenocentric axial dipole (SAD) field geometry: a dipole in the centre of the Moon and aligned along the spin axis. Additionally, although true polar wander is not required by our data, true polar wander paths inferred from some independent studies of lunar hydrogen deposits and crustal magnetic anomalies^4,5,6 are consistent with our measured paleoinclination.

阿波罗样本的古地磁研究表明，月球产生了至少 20 亿年的磁场^1,2. 然而，月球磁场的几何形状在很大程度上仍然是未知的，因为基本上所有阿波罗样本的原始方向都没有得到很好的限制。随着时间的推移确定月球磁场的方向可以阐明月球发电机的动力机制以及月球是否经历了真正的极地漂移。在这里，我们展示了由阿波罗 17 号母马玄武岩 75035 和 75055 记录的 37 亿年前的月球磁场测量结果。我们发现 75035 和 75055 记录的平均古强度约为 50 μT。此外，我们可以从75055的磁化方向及其母巨石的分层推断，当时的磁场倾角为34±10°。我们恢复的倾向是一致的，但不要求，一个以硒为中心的轴向偶极子 (SAD) 场几何结构：月球中心的偶极子并沿自旋轴对齐。此外，虽然我们的数据不需要真正的极地漂移，但从对月球氢沉积物和地壳磁异常的一些独立研究中推断出真正的极地漂移路径^4,5,6与我们测量的古倾角一致。