14 DAY TRIAL // A collaboration of investigators from the Harvard University, the Massachusetts Institute of Technology (MIT) and the Institut de Physique du Globe de Paris, in France, recently provided a simple explanation for why some parts of the lunar crust contain swaths of highly magnetic material.
This was first discovered about 50 years ago, during some of the first surveys ever to be conducted at Earth's natural satellite. Since that time, numerous researchers have proposed a host of theories to explain why the materials exist.
Over the years, those explanations have become increasingly complex. What the new study provided was a very simple answer to this mystery. The group proposes that the magnetic material comes from asteroids, and that they were produced during past impacts.
Details of this simple and elegant proposal appear in the March 9 issue of the top journal Science. The research team believes that a massive impact occurred between the Moon and an asteroid some 4 billion years ago, shortly after the object formed.
This impact would have left behind an enormous crater and a lot of iron-rich, highly-magnetic rock. The Moon did have its own magnetic field at one point, but it was never really strong enough to allow for the formation of such anomalous rocks, according to Astrobiology Magazine.
“The conundrum has always been that the magnetism we see on the Moon is not correlated with any surface geology,” explains Sarah Stewart-Mukhopadhyay, who holds an appointment as the John L. Loeb associate professor of the natural sciences at Harvard.
“The theory that has been most commonly cited to explain it is an 'impact-induced field,' in which an impact concentrates and amplifies the Moon's magnetic field. But it was difficult to test – people have tried to model it, but it is right at the edge of what could work,” she explains.
Most of the highly-magnetic material on the Moon lies around the edges of the South Pole-Aitken Crater, a 2,400-kilometer (1,490-mile) hole in the floor of the lunar south pole. “It is possible that metallic iron from an asteroid could have been magnetized by the impact,” Stewart-Mukhopadhyay says.
This proposal makes sense when it's placed in the context of our solar system's history. During the Late Heavy Bombardment, around 3.8 billion years ago, numerous space rocks impacted all the planets and moons in the inner solar system.