Did The Moon Once Have A Magnetic Heart Stronger Than Earth's?

John Hopton for redOrbit.com – Your Universe Online

Samples of moon rocks brought back by the Apollo astronauts are a gift that just keeps on giving, and a new study has shed more light on the fact that the moon once had its own magnetic field, just like the Earth has today. Scientists, however, are unsure what sustained it or why it ended.

The moon is only one percent of the Earth’s mass, and yet it is thought to have had magnetic heart that at one time beat stronger than our own planet’s. Experts have been divided as to the source of the magnetic field, with some theorizing that the moon provided its own magnetism, like the Earth, through a moving, molten metallic core which acted as a dynamo. A global magnetic field would therefore be generated through electric currents. Others insisted that lunar soil picked up magnetic fields from impacting asteroids and other bodies, which resulted in recurring but temporary electrically charged plasmas.

Recent analysis of lunar samples has shown that the moon had a dynamo-driven magnetic field that was “surprisingly intense (stronger than Earth’s field today) and long-lived, persisting from at least 4.2 billion years ago until at least 3.56 billion years ago,” according to planetary scientist Benjamin Weiss, with the Massachusetts Institute of Technology (MIT). Researchers are unsure as to when the moon’s magnetic field ended, but the size of the field suggests a dynamo system similar to Earth’s.

“We see this super strong field and then it just drops off a cliff. Everywhere points to this large-scale geophysical process,” Weiss told Discovery News reporter Irene Klotz.

Clément Suavet, also with MIT, said last year that upon discovering that the moon’s magnetic field survived longer than previously thought and survived the period of heaviest cratering, he believed that impacts could be dismissed as the cause of the dynamo’s origin. However, impacts may have acted as a catalyst of greater activity within the core. Another theory is that “gravitational tugs” from Earth may have kept the fluid moving by splitting the moon’s solid mantle and molten core.

“Planetary dynamos are generated by the process of induction,” says Weiss, “in which the energy of turbulent, conducting fluids is transformed into a magnetic field. Magnetic fields are one of the very few outward manifestations of the extremely energetic fluid motions that can occur in advecting planetary cores.”

He adds that, “The motion of Earth’s liquid core is powered by the cooling of the planet, which stirs up buoyant fluid from the surrounding liquid — similar to what happens in a lava lamp. We have recently argued from magnetic studies of Apollo samples that the moon also generated a dynamo in its molten metal core.”

Alignment of electrons in the rock is the clue to the history of the moon’s magnetic field, representing the field’s significant strength as well as the way in which the dynamo was “stirred up.” Weiss says that, “The record of past magnetic fields are recorded in rock, the microscopic alignment of electrons in the rock, like little compass needles. The more of them that are aligned, the stronger the magnetic field.”

“Maybe every time the moon was hit by a big impact it underwent this major rotation, the north pole became a different location,” he added.

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