The Moon’s magnetic field was twice as strong as Earth’s for billions of years

Vibrating invisible electric and magnetic forces surround Earth, protecting us from cosmic radiation and thus making life possible. The magnetic field is thought to be created by the activities of the churning liquid metals at the planet’s core.

Recently scientists discovered that an iron “snow'” is always falling from the outer to the inner core at incredible temperatures and pressures.

Now researchers at MIT have discovered that the Moon also had a magnetic field that lasted for at least two billion years. Surprisingly, the field was twice as strong as the Earth’s when our lunar neighbor’s orbit was twice as close, around four billion years ago.

Over time the field weakened but persisted until as recently as a billion years ago.

The recent video from NASA below shows how Earth’s magnetic field vibrates like a drum:

Lunar dynamo

Similar to Earth, the Moon’s magnetic field may have been created by a churning electrically charged liquid iron core. However, this is not known for sure. Scientists think the gravitational forces of the Earth generated the motion they call a lunar “dynamo.”

“The magnetic field is this nebulous thing that pervades space, like an invisible force field,” says Benjamin Weiss, professor of Earth, atmospheric, and planetary sciences at MIT. “We’ve shown that the dynamo that produced the moon’s magnetic field died somewhere between 1.5 and one billion years ago, and seems to have been powered in an Earth-like way.”

The researchers studied lunar rocks from NASA’s Apollo missions. Almost all the rocks on the Moon’s surface date back three to four billion years, possibly formed from volcanic eruptions. The volcanic activity seems to have stopped around three billion years ago.

The rocks contain a record of the magnetic field during the time of formation measured in microteslas.

“The team took the samples back to the lab and first analyzed the orientation of each rock’s electrons, which Weiss describes as ‘little compasses’ that either align in the direction of an existing magnetic field or appear in random orientations in the absence of one.”

The missing record

Interestingly, the researchers have been unable to find many samples from more recent times, and most samples appear to have endured a “massive impact” around one billion years ago.

“The past three billion years of lunar history has been a mystery because there’s almost no rock record of it,” Weiss told Newsweek.

What stopped the dynamo?

The researchers think that the Moon was able to retain its magnetic field for an extraordinarily long time but, of course, eventually stopped.

Weiss noted that the Moon’s dynamo seems to have outlasted the dynamo on Mars, even though Mars is twice as large. The scientists aren’t sure what made the relatively small Moon’s moving core so long-lived.

“A strong field on the moon may have shielded the surface from the solar wind, the supersonic plasma emitted from the sun,” study author Benjamin Weiss told Newsweek. “This may have prevented the surface from being space weathered and the soil becoming rich in solar gases like it is today. Furthermore, the Moon was likely about twice as close to the Earth during the time the Moon was inferred to have a strong magnetic field compared today.”

Over the years, the Moon moved away from Earth, and the pull of gravity diminished. As a result, the Moon’s core began to crystalize. The process took billions of years, and eventually, the core fully crystalized, killing the dynamo. The magnetic field vanished and the Moon was bombarded by radiation and solar debris. We can see the scars with our naked eyes today.

Our rare and wonderful Moon

Today, the Moon’s gravitational forces continue to make life as we know it possible by stabilizing our orbit and creating the tides.

Earth’s Moon is thought to be rare in all the universe. It is unusually large for a moon and may have formed when a Mars-sized body collided with the Earth. The resulting debris collected together through the forces of gravity and the Moon settled into orbit, avoiding further collisions that could have blasted it away into space.

Most moons are thought to result when smaller floating bodies are trapped in a planet’s gravitational forces. Although all moons can impact the planets they orbit, our Moon has a particularly strong and critical effect on life.

Now we can only wonder how life may have been different if the Moon’s dynamo had continued to churn until more recent times. Would life have been possible on the surface? We can only guess but will learn much more as we prepare to travel back to the Moon in the near future.


“The space agency plans to land two people near the lunar south pole by 2024, and at least one of those pioneers will be a woman. So the coming giant leap will be quite different than the Apollo moon missions, NASA chief Jim Bridenstine stressed.”

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Featured image: Composite from screenshots via YouTube






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