The phenomenon endured for about half a billion years

Jan 27, 2012 21:31 GMT  ·  By

In a paper published in the January 27 issue of the top journal Science, experts propose that the Moon's magnetic field in fact endured for a lot longer than previously estimated. At the same time, its strength may have been underrated in past investigations, the same team indicates.

But the most important conclusion researchers came to was that the Moon had a natural dynamo at its core around 3.7 billion years ago. Whether its magnetic fields were created by a dynamo, or by plasma produced during asteroid collisions, was a matter of debate in the scientific community for years.

A dynamo effect is produced by a solid nucleus spinning in a fluid core. This is how Earth's magnetic field is produced, and it will continue to be renewed until the core solidifies entirely. At that point, the planet will be left defenseless against cosmic rays and solar radiation.

Experts know the Moon had a magnetic field because traces of magnetism were discovered in rock samples brought back by the Apollo missions. What the latest investigation did was establish that the natural satellite indeed had a core capable of driving a dynamo effect, long ago.

The impact theory – the other alternative to this explanation – held that plasma produced during asteroid impacts on the surface of the Moon was responsible for the traces of magnetism investigators found in the Apollo samples, Space reports.

However, the new research demonstrated that the Moon had a molten outer core surrounding a solid iron core for at least 500 million years, between 4.2 and 3.7 billion years ago. This period of time is a lot longer than experts arguing for this theory ever calculated.

“The findings in general were a big surprise. When we selected this sample, we had an idea that it'd have a good magnetic record, but we didn't have an idea how good it would be,” Massachusetts Institute of Technology (MIT) geologist and lead study author Erin Shea explains.

“The implications are amazing and interesting. If the moon had a dynamo that lived a long time, why not an asteroid like Vesta or a smaller asteroid?” the expert adds. Vesta is the largest asteroid in the solar system, and is cataloged by many as a protoplanet (a planetary embryo that never finished developing).

What the team is interested in now is determining whether the Moon's dynamo effect remained on for 500 million years, or whether it used to stop and restart at regular intervals. Establishing this could finally certify that the object was indeed once a part of our planet, separated during a cosmic impact with a Mars-sized planet.