Washington, Jan 16. A new study has suggested that the moon, in its ancient past, had an Earth-like core, which may explain its mysterious magnetic field.
Magnetic moon rocks picked up on the Apollo missions in the late 1960s and early 1970s surprised scientists, who thought no such field existed on the moon.
Since then, two competing theories have emerged for the moon’s magnetism: shockwaves locking in magnetic fields generated by meteors slamming into the heavily cratered surface, or the movement of heat inside a molten metallic core.
According to a report in National Geographic News, new analysis of the oldest known “unshocked” Apollo sample—a rock never affected by a meteor impact—favors the iron core theory.
That’s because the 4.2-billion-year-old rock has a history of longer, slower cooling periods, a discovery more consistent with the core’s influence than occasional meteor impacts.
“There’s growing evidence for the internal structure of the moon having a core, and this study supports those theories,” said study lead author Ian Garrick-Bethell, a Ph.D. student from Massachusetts Institute of Technology (MIT).
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, according to Garrick-Bethell.
Furthermore, the rock dates to an era during which the moon would have most likely had an active core, the study authors said.
According to Pierre Rochette, a geoscience professor at Universite d’Aix-Marseille 3 in France, the result “makes again a strong case for both the presence of a metallic core in the moon and more firm magnetic evidence.”
The new moon research can also tell scientists more about the moon itself, such as when its dark features known as “mare plains” formed.
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,” he added.
ANI
