guardian: Nowadays, the moon has no global magnetic field, but that was not always the case; between 4.25bn and 3.56bn years ago, the lunar magnetic field was similar to that of the Earth. by Nicola Davis
'The field is thought to have been generated by the churning movement of fluids within the moon’s molten core – a sort of lunar dynamo.
'But scientists have long puzzled over when the magnetic field disappeared, with previous research unable to tell whether the field had disappeared completely by 3.19bn years ago or had lingered on in a weaker form.
'“One the question that we were trying to answer was really when did the magnetic field cease, [so] we wanted to study younger lunar samples – rocks that are younger than 3.56bn years old,” said Sonia Tikoo, a planetary scientist and co-author of the research from Rutgers University.'