Since the Apollo missions returned from the Moon, we have not understood the lunar samples they brought home.
Some of the rocks are more than 3 billion years old and appear to have been formed in the presence of a strong geomagnetic field. The Moon is too small and dense to have a magnetosphere.
Unlike Earth, the Moon's insides are not constantly churned with electrical material that causes a geomagnetic field. Why do lunar rocks tell us differently?
It's possible that the Moon didn't freeze over as quickly as we thought, and that it might have been slightly molten a few billion years ago.
The strength of the field is unlikely to match what the surface rocks are telling us, even if it was sustained for a long time.
Scientists think the Moon used to jiggle more, which kept the liquid in its belly from moving. The Moon could have gotten a boost from meteorites.
Researchers have previously thought of a new way to answer the question, suggesting that the lunar surface was exposed to short bursts of magnetic activity.
The model proposed by the duo from Brown University in the US is about how these fields might form.
Alexander Evans said that he was thinking about how to power a strong magnetic field continuously over billions of years.
Our model shows how that can happen, and it's in line with what we know about the Moon's interior.
The Moon's core was not very hot in the first billion years of its existence. The heat from the Moon's interior didn't have a place to go, which causes molten material to move. The hotter bits tend to rise until they cool, while the denser bits sink until they heat up.
The pot generated a magnetic field.
As the object cooled, the molten rock would have solidified at slightly different rates, and it was likely that the Moon was covered in molten rock in its youth.
The densest minerals, such as olivine and pyroxene, would have sunk to the bottom and cooled first, while lighter elements like titanium would have floated to the top and cooled last.
The rock would have weighed more than what was below it, causing it to fall through the mantle and into the core.
At least a hundred blobs of titanium-rich material hit 'rock bottom' in a billion years, according to researchers.
Each time one of these massive slabs, about 60 kilometers (37 miles) in radius, connected with the core, had a mismatch in temperature, the current would have been strong enough to generate a pulse of magnetism.
Evans says it's like a drop of water hitting a hot skillet.
A lot of heat can evaporate from the core when it is cold. The strong magnetic fields are caused by that.
Different lunar rocks have different magnetic signatures. The Moon's magnetosphere may not have been constant.
The authors want to see if they can detect a weak magnetic background that is only occasionally pierced by a stronger force.
Nature Astronomy published the study.
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