A piece of a selenar rock brought from the moon in 1971 proves that it had a magnetic field one billion years ago.

The discovery shows that Earth’s natural satellite had a core which melted nearly 1-2.5 billion years ago, followed by the solidification process.

Researchers from MIT, Rutgers University and Berkeley, California, analyzed a piece of rock brought by the Apollo 15 mission, indicating the existence of a 5 microtesla magnetic field [The tesla (symbol T) is a derived unit of the strength of a magnetic Field in the International System of Units].

It is small compared to Earth’s, Terra having an area between 25 and 65 T and a core made of iron and nickel.

It is assumed that 4.5 billion years ago there was a massive impact between our planet and another Mars-sized object, impact that was enough to give the Moon a magnetic field of 70 T, but as the satellite cooled, the magnetic field became weaker.

No wonder it disappeared over time, the true mystery is how it resisted so much. Just 3.56 billion years after the collision, the body peaked, then dropped to only 4 T after just 400 million years.

Past cosmic impacts have played an important role through the generated thermal energy, but there is another possibility: the heat generated by the crystallization of the minerals in the core stirred the particles by convection enough to generate a magnetic field.

The rest of the data remains unknown.

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