The moon’s “internal engine” stopped 1 billion years ago, causing its magnetic field to fade away

Now, new research suggests that about a billion years ago, when the moon’s “internal engine” stopped working, the moon’s once-protected magnetic field faded away. To determine the strength of the previous lunar magnetic field, the researchers analyzed samples of rocks on the moon’s surface that originated from a large-scale collision. As the celestial impact lava gradually cools, its internal tiny particles are rearranged with the moon’s magnetic field, becoming a snapshot of the strength and direction of the magnetic field at that time.

A billion years ago, the moon’s magnetic field dropped to 0.1 micro-Tesla, about 500 times the current Earth’s magnetic field, suggesting that the “engine” that drives the moon’s magnetic field, driven by the moon’s nucleus crystalline material, has stopped operating.


The Earth’s magnetic field is the product of the current produced by liquid metals as it moves through the core, which is essential for protecting people from the flow of charged particles from the sun. Scientists now discover that the moon once had a powerful magnetic field, but now it has long since disappeared.

The moon is still slowly moving away from us, about 2.5 meters a year, and Professor Weiss and colleagues have previously found that about 4 billion years ago the moon’s magnetic field was 100 micro-Teslas, about twice the intensity of the Earth’s magnetic field today.

Benjamin Weiss, a planetary scientist at the Massachusetts Institute of Technology, said the moon’s powerful magnetic field protects the moon’s surface from the solar wind, a supersonic plasma released by the sun that could prevent the surface from being weathered and avoid the moon’s soil containing large amounts of solar gas. Just like today. It is inferred that the moon’s magnetic field was twice as far away from Earth as it is now.

The moon is still slowly moving away from us, about 2.5 meters a year, and Professor Weiss and colleagues have previously found that about 4 billion years ago the moon’s magnetic field was 100 micro-Teslas, about twice the intensity of the Earth’s magnetic field today.

The team determined this by analyzing a lunar rock sample formed by volcanic activity on the moon’s surface, and when the ejected material cools and condenses, the tiny particles that make up the rock will be consistent with the direction of the moon’s magnetic field, like a miniature frozen compass, capturing a snapshot of the moon’s magnetic field strength and direction.

In fact, there are limitations to the current measurement of the moon’s early magnetic field, which researchers analyze based on forming lava, but volcanic activity on the moon has largely stopped about 3 billion years ago.

Weiss points out that the moon was a mystery 3 billion years ago because no rock records have been found during that period, and that volcanoes are not the only way for the moon to form lava, and that some molten material forms when certain objects collide with the moon’s surface.

In 2017, the team found that the moon formed rocks during a celestial collision 2.5 billion years ago, and their research confirmed that the moon’s magnetic field had dropped to about 10 micro-Teslas.

In their latest study, Professor Weiss said they found similar rock structures, possibly formed after a large impact on an object about 1 billion years ago, presumably no more than 0.1 microtra.

The study showed that the moon’s “internal engine” that drives the magnetic field was switched off, and the team believes that the moon’s magnetic field may be driven by two different processes. Initially, the moon’s orbit approached the Earth, causing gravitational agitation of liquid in the moon’s core, creating an engine effect that powers the magnetic field, but as the distance between the Earth and the moon increased, a second process known as “nuclear crystallization” may be even more important.

In the process, the moon’s dense iron core gradually formed and stirred the surrounding liquid matter outside the core, creating a magnetic field. When the moon’s core is completely detached from the shell and gradually crystallized, the “internal engine” that drives the magnetic field stops working, although scientists still don’t know whether the process occurred suddenly or whether it would suddenly occur before the moon’s magnetic field disappeared.

Professor Weiss points out that magnetic fields are pervading space, like an invisible force field, and we have now shown that the engines that produced the moon’s magnetic fields disappeared 1.5 billion to 1 billion years ago.

Researchers are reported to have studied the moon’s “internal engine” for at least 2 billion years because the moon is a smaller object that cools faster than planets. “Mars is about twice the diameter of the moon, but it is widely believed that the ‘internal engine’ of the Martian magnetic field ended 4 billion years ago, and that there must be an unusual secret about the ‘internal engine’ of the lunar magnetic field,” Weiss said. “

With the preliminary study completed, the researchers now hope to measure more than just the strength of the lunar magnetic field, Professor Weiss said: “We are trying to use the Apollo lunar rock sample to measure the direction of the moon’s magnetic field in ancient times to create the original orientation of the lunar magnetic field.” “The latest study is now published in the journal Science Advances.