Magnetizations within lunar rocks indicate that the ancient Moon produced an internally generated magnetic field^1,2,3,4. Yet the long-lived field intensities of 40–120 μT inferred for the ancient Moon¹ are unsustainably high and cannot be reconciled with the small lunar core size, requiring three orders of magnitude more energy than deemed possible⁵. Here, we report that a 1 Gyr protracted foundering of cool, dense Ti-rich material initially emplaced at shallow depths can generate the high-intensity magnetic fields (≥50 μT) preserved within returned lunar samples through temporary episodes of elevated superadiabatic heat flow (≥50 mW m⁻³) out of the lunar core. Our results can simultaneously explain both the high magnitude and large-scale variability in field intensities before at least 3.5 Gyr ago¹ while still permitting lower fields to have persisted thereafter.

月球岩石内的磁化表明古代月球产生了内部产生的磁场^1,2,3,4。然而，为古月球¹推断的 40-120 μT 的长寿命场强度高得不可持续，无法与小月球核心尺寸相协调，需要比认为可能的能量多三个数量级的能量⁵。在这里，我们报告说，最初放置在浅层深度的冷、致密富钛材料的 1 Gyr 长时间沉降可以通过临时升高的超绝热热流产生高强度磁场（≥50 μT）保存在返回的月球样本中。 ≥50 mW m ^{- 3}) 在月核之外。我们的结果可以同时解释至少 3.5 Gyr 前¹之前场强的高幅度和大尺度变化，同时仍然允许较低的场在此后持续存在。