MIT scientists searching for answers to the presence of highly magnetic material detected on the far side of the moon are unveiling new clues that could soon help solve the mystery.
According to new research, the team believes a massive impact that struck the Moon’s Earth-facing side caused a plasma cloud in the atmosphere and associated shockwave, which magnetized several surface rocks on its far side.
Directly sampling some highly magnetic moon rocks to confirm the hypothesis may be viable since many ideal targets are located around the lunar south pole near NASA’s planned Artemis mission.
“There are large parts of lunar magnetism that are still unexplained,” explained Isaac Narrett, a graduate student in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS) and lead author of the study detailing the theory. “But the majority of the strong magnetic fields that are measured by orbiting spacecraft can be explained by this process, especially on the far side of the moon.”
Highly Magnetic Material on the Far Side of the Moon Still a Mystery
Most scientists believe that Earth’s magnetic field is generated by a rotating core of molten lava that creates an electrical ‘dynamo’ effect as it spins. Today, the Moon lacks a global magnetic field and an active dynamo, although scientists believe it once had a molten, rotating core that generated a magnetic field in the distant past.
When Apollo astronauts brought samples of lunar rocks to Earth in the 1960s and 1970s, analysis indicated the remnants of a strong magnetic field in the moon’s past. Several orbiting spacecraft have also detected signs of magnetism on the moon’s surface, seemingly confirming the ancient magnetic field theory.
Still, those same orbital readings also presented researchers with a lunar mystery: some of the surface material on the far side of the moon appeared to be highly magnetic. While a magnetic field in the moon’s distant past could account for some of the mysterious magnetism, the high levels and localized concentrations on the moon’s far side left scientists scratching their heads.
According to the study authors, one previous effort tried to connect the “missing magnetism” to the force of a massive lunar impact event combined with the presence of a weak magnetic field caused by the sun. However, that study still could not explain the highly magnetic material.
The MIT team has proposed a new theory to explain the confusing data. According to their simulations, a massive impact event that generates a seismic shockwave and a moon-wide plasma plume, combined with a theoretical ancient magnetic field caused by a now-extinct rotating molten lunar core, could explain how some surface material on the far side of the moon is highly magnetic.
Simulations Offer Support for New Mysterious Magnetism Theory
First, the MIT team estimated the size of the moon’s ancient rotating core. This allowed them to determine the likely strength of the field at around one microtesla, which is 50 times weaker than Earth’s present-day magnetic field.
Next, the team employed simulations by team member Katarina Milijovic to test various lunar surface impact scenarios powerful enough to create the Imbrium basin. This site was chosen because it’s one of the largest impact craters on the Moon’s near side, and researchers theorize that the force from the impact could have influenced magnetic anomalies on the far side.
After simulating the impact event, the team simulated the size and shape of the huge plasma cloud that such an impact would have created. These results were further analyzed using an adaptation of a code developed by collaborators at the University of Michigan that simulated how the plasma cloud of vaporized lunar surface material would likely have interacted with the moon’s weak magnetic field.
Although the simulations showed some of the plasma cloud expanding out into space due to the moon’s virtually nonexistent atmosphere (formally known as its exosphere), the vast majority streamed around the natural satellite until it concentrated on the far side of the moon, right where the highly magnetic material had first been detected. The simulation data also showed how the compressed plasma would have briefly amplified the moon’s theoretical magnetic field for around 40 minutes before it returned to its previous baseline. While the simulations showed the resulting spike wasn’t substantial enough to account for the mysterious magnetism, the researchers inserted one more variable designed to “shake up” the results.
How the Moon Played a Magnetized Game of 52 Pickup
When evaluating their simulation data, the team noted that the massive impact, powerful enough to cause their traveling plasma plume, would have also resulted in an enormous pressure wave. As this pressure wave would have moved through the moon like a seismic shock, the researchers say it would have “jittered” the surface material, including the rocks on the far side of the moon. This jittering would have also resulted in an “unsettling” of the electrons within the rocks. Since electrons naturally orient their spins to any external magnetic field, after they settled, their orientations would have all assumed a new orientation based on the brief interaction with the magnetic field.
“It’s as if you throw a 52-card deck in the air, in a magnetic field, and each card has a compass needle,” Weiss explained. “When the cards settle back to the ground, they do so in a new orientation. That’s essentially the magnetization process.”
Confirming the new hypothesis will likely require directly measuring lunar rocks sampled from several lunar locations. Fortunately, the landing spot for NASA’s upcoming Artemis mission is extremely close to the location of the highly magnetic mystery rocks near the lunar south pole. Ultimately, the research team believes their study offers the likeliest explanation for the moon’s mysterious magnetism and the best way to confirm it.
“For several decades, there’s been sort of a conundrum over the moon’s magnetism — is it from impacts or is it from a dynamo?” MIT researcher and fellow team member Rona Oran said. “And here we’re saying, it’s a little bit of both. And it’s a testable hypothesis, which is nice.”
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.