The moon's magnetic field may have been altered by huge sinking rocks

Moon rocks collected by the Apollo missions sparked a mystery because they showed signs of having formed under a magnetic field as strong as Earth’s, but it was unclear how a body as small as the moon could have created such a field. Now there is a potential solution.

Alexander Evans at Brown University in Rhode Island and Sonia Tikoo at Stanford University in California propose that giant rocks as large as 60 kilometres across once sank through the moon’s mantle and stirred up the interior, generating sporadic, relatively…