Reading the moon's diary, one speck of dust at a time

Magnetism on the moon has always been a bit confusing. Remote sensing probes have noted there is some magnetic signature, but far from the strong cocoon that surrounds Earth itself. Previous attempts to detect it in returned regolith samples blended together all of the rocks in those samples, leading to confusion about the source—whether they were caused by a strong inner dynamo in ages past, or by powerful asteroid impacts that magnetized the rocks they hit. A new study from Yibo Yang of Zhejiang University and Lin Xing of the Chinese Academy of Sciences, published recently in the journal Fundamental Research, shows that the right answer seems to be—a little of both.