Early Lunar Magnetism

@article{GarrickBethell2009EarlyLM,
  title={Early Lunar Magnetism},
  author={Ian Garrick‐Bethell and Benjamin P. Weiss and David L. Shuster and Jennifer Buz},
  journal={Science},
  year={2009},
  volume={323},
  pages={356 - 359}
}
It is uncertain whether the Moon ever formed a metallic core or generated a core dynamo. The lunar crust and returned samples are magnetized, but the source of this magnetization could be meteoroid impacts rather than a dynamo. Here, we report magnetic measurements and 40Ar/39Ar thermochronological calculations for the oldest known unshocked lunar rock, troctolite 76535. These data imply that there was a long-lived field on the Moon of at least 1 microtesla ∼4.2 billion years ago. The early age… 
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