Apollo 12 magnetometer: measurement of a steady magnetic field on the surface of the moon.

@article{Dyal1970Apollo1M,
  title={Apollo 12 magnetometer: measurement of a steady magnetic field on the surface of the moon.},
  author={P Dyal and C W Parkin and Charles Sonett},
  journal={Science},
  year={1970},
  volume={169 3947},
  pages={762-4}
}
The Apollo 12 magnetometer has measured a steady magnetic field of 36 +/- 5 gammas on the lunar surface. Surface gradient measurements and data from a lunar orbiting satellite indicate that this steady field is localized rather than global in its extent. These data suggest that the source is a large, magnetized body which acquired a field during an epoch in which the inducing field was much stronger than any that presently exists at the moon.