Mystery of Moon's Lost Magnetism

This illustration shows one suggested mechanism for creating an ancient magnetic field on the moon. In this scenario, impacting space rocks on the moon would create instability in the moon's core that could lead to a dynamo that creates a magnetic field.

CREDIT: M.-H. Deproost, ORB, Belgique

One of the abiding mysteries of our moon is why it apparently once had a magnetic field.

Now two teams of scientists have offered two separate, but potentially complementary, explanations.

When Apollo astronauts brought back samples of moon rocks from their lunar landing missions in the 1960s and '70s, some of them shocked scientists by being magnetic.

That means that individual rocks might have a magnetic north and south pole and a small magnetic field of their own.

This can happen to rocks with the right minerals inside them, if they cool in the presence of a magnetic field.

The problem is, scientists had no idea that the moon had ever had a magnetic field, and were at a loss to explain how that might have happened.

A magnetic field is generated by what's called a dynamo, which is caused by the fluid motion of a conducting material, such as liquid iron.

In the case of the Earth's magnetic field, this motion occurs in the planet's outer core, and is caused by the convection of heat.