There is a strong magnetic field around the Earth which is created by the rotation of liquid iron present in the core of the planet. Earth’s magnetic field can be almost as old as that of Earth. Scientists believe this idea is the exact opposite of the Moon, which today is completely devoid of a magnetic field. But has the core or the core of the Moon generated a magnetic field in the past? John Torduno from the University of Rochester, USA, gave detailed information on this topic.
Has the magnetic field ever been present on the Moon?
In the 1980s, geophysicists studying rocks brought by astronauts from Apollo concluded that the Moon once had a magnetic field as strong as Earth’s. But a strong magnetic field requires a power source, and the Moon’s core is relatively small. For decades, scientists have struggled to solve the riddle of how such a small nucleus could create a strong magnetic field.
I am a professor of geophysics and have been studying the Earth’s magnetic field for over 30 years. I recently assembled a team to reexamine the evidence for lunar magnetism using new scientific techniques. We discovered that the Moon didn’t really have a magnetic field for a long time. The discovery not only transforms the modern understanding of the geological history of the Moon, but it also has major implications for the presence of resources on the Moon that could be important for future human exploration.
Why the magnetic moon?
Some rocks have the extraordinary ability to retain records of past magnetic fields when they contain minerals containing iron atoms that align with a magnetic field as the rock cools and solidifies. The best magnetic minerals for preserving evidence of a field are tiny – a thousand times smaller than the width of a human hair – because it takes a lot of energy to rearrange their atoms.
Geophysicists who study ancient magnetism are recreating this process, warming rock samples in the presence of known magnetic fields and warming the rock with the orientation of the iron atoms before warming up. Let’s compare the new alignment. It helps researchers learn about past magnetic fields.
Why the study of magnetism in lunar soil is difficult
The first researchers studying the first rocks brought from the Moon by American astronauts wanted to use this method to study the magnetism of the Moon. But they had to face difficulties. Moon rocks contain a certain type of iron – called parent iron – which is easily changed by heat. Additionally, the original iron grains in moon rocks are sometimes relatively large, making them less likely to reliably register past magnetic fields.
Since the 1970s, geophysicists have used alternative non-temperature methods to study the magnetism of the Moon. They found that some lunar samples recorded strong magnetic fields, suggesting that the Moon had a magnetic field for more than 2 billion years. But this result deepened the puzzle. The question of how the Moon’s core could produce a strong magnetic field remained unanswered.
an alternative theory
In experiments, some Apollo samples showed signs of strong magnetic fields, but others did not. Some researchers have attributed the missing magnetization to the presence of large grains of core iron which were poor magnetic recorders. But many samples also contained tiny grains of iron that should have recorded evidence.
The no-heating technique used by researchers on Apollo samples has long been skeptical. Some scientists called them a “last resort” and concluded that the uncertainty of the data collected in this way was so great that any interpretation should be seen as speculation. Alternatively, another group of scientists have suggested for decades that when meteorites collide with the Moon, they form a dust-filled plasma – a gas of ions and electrons – which can generate a strong magnetic field and a impact. Region.
Study of lunar magnetism using the heating technique
In 2008, geophysicist Kristin Lawrence decided to revisit the question of lunar magnetism using an improved heating technique. Unlike the researchers who initially studied the samples, she was unable to locate definitive evidence of a past magnetic field. The approach used by Lawrence and his team was better than testing without heating, but his results were still inconclusive. She realized she was able to draw a conclusion, and that’s when she turned to me and my lab for help.
In 2011, Lawrence brought us a collection of lunar samples to test. We were developing techniques to identify millimeter-sized silicate crystals that contain only very small grains of iron and have ideal recording properties. We then used an ultra-sensitive superconducting magnetometer and a special carbon dioxide laser to quickly heat these samples, to prevent their iron minerals from changing. We found that almost all of the rocks had extremely weak magnetic signals.
absence of magnetic field on the moon
At the time of this first test, we were still improving the method, so we couldn’t say for sure whether the samples formed on the Moon without a magnetic field. But we are improving our testing methods, and last year we decided to review the Apollo samples. We have conclusively found that some samples actually contained magnetic minerals capable of preserving high-fidelity signals from old magnetic fields. But the rocks had registered no such sign. This suggests that the Moon has not had a magnetic field for most of its history.
John Tarduno, University of Rochester Rochester (United States)