Ancient Moon Had Earthlike Core?

Christine Dell'Amore
National Geographic News
January 15, 2009

The mystery of the moon's magnetic field may finally be explained by the presence of an Earthlike core, a new study says.

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.

New analysis of the oldest known "unshocked" Apollo sample—a rock never affected by a meteor impact—favors the iron core theory, researchers say. (See photos of moon explorers.)

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.

(Related: "Moon Has Iron Core, Lunar-Rock Study Says" [January 11, 2007].)

Relic Thinking

Before the Apollo missions, lunar scientists thought the moon was just a rock—a relic of the solar system's formation that never formed a core.

Detecting what's at the moon's heart is tricky, with only ambiguous data available, said Garrick-Bethell, whose work appears tomorrow in the journal Science.

Even Earth's core is only known through seismology, the study of earthquakes and the seismic waves that pass through the planet, he added.

This uncertainty has pushed lunar scientists to adopt creative approaches, such as paleomagnetism—tracing the moon's ancient magnetic field.

Continued on Next Page >>




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