In the new study, Garrick-Bethell and colleagues built on paleomagnetism with another technique of studying moon rocks: Looking at their heat—or thermal—histories.
The team was able to determine that the rock heated and then cooled only twice in 4.2 billion years.
These cooling events were more drawn out than what would be expected if a barrage of meteors had magnetized the rock.
Magnetic fields created by meteor impacts usually last a day at most, Garrick-Bethell said.
Furthermore, the rock dates to an era during which the moon would have most likely had an active core, the study authors say.
Pierre Rochette, a geoscience professor at Université d'Aix-Marseille 3 in France, said the result "makes again a strong case for both the presence of a metallic core in the moon and more firm magnetic evidence."
The research could also reveal more about the wider solar system, added Rochette, who was not part of the study.
For instance, there is a long-held consensus that objects in the solar system smaller than than Mars, can't sustain magnetic fields.
With more studies pointing to the moon's core, in addition to signs that Mercury and satellites of Jupiter and Saturn have cores, experts are being forced to "go backward in that direction," Rochette said.
Likewise, the new moon research can also tell scientists more about the moon itself, such as when its dark features known as "mare plains" formed, study lead author Garrick-Bethell said.
The large basaltic areas were likely caused by ancient volcanic eruptions.
"This is related to features everyone looks up and sees, these dark plains," Garrick-Bethell said.
"If we can do this study for lots of other rocks, we have the potential to unravel the internal thermal history and evolution of the moon."
SOURCES AND RELATED WEB SITES