The magnetic field persisted well beyond its midlife, well after its expected disappearance time.
Scientists discovered that the moon's magnetic field measured approximately two to four microteslas about two billion years ago - which is less than 10 percent of the Earth's current surface magnetic field.
Ross Mitchell, co-author of the paper from the Institute of Geology and Geophysics in Beijing, stated that whereas some people assumed the moon's magnetic field had long disappeared by then, their study showed that it was "at least still barely operational".
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According to planetary scientist Benjamin Weiss of the Massachusetts Institute of Technology, although not involved in the current research, a mild yet enduring magnetic field likely originated from ongoing interior processes such as the potential crystallization of the moon's core or interactions between its core and mantle.
These processes would have kept the moon's magnetic field, also called the lunar dynamo, active for billions of years.
Weiss wrote in a review article interpreting the results, "The moon goddess's elixir appears to have worked its magic."
The results imply that the long-lasting magnetic field could have protected the moon's surface from solar radiation, allowing volatile compounds, like water, to remain.
Understanding such details of the moon's magnetic history helps us gain valuable insights into planetary habitability and evolution.
the Apollo missions suggested its presence over three billion years ago, with strengths comparable to Earth's current magnetic field, between 25 and 65 microteslas.
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The exact duration of the lunar dynamo remained unknown.
Analyzing the American Apollo samples posed a challenge due to their relatively older age, large iron grains which resulted in poorly preserved magnetic signals and other limitations, Weiss pointed out.
missions five decades ago.
The researchers chose nine teeny-weeny pieces of basalt for the study - each 3-8 millimeters in size and weighing under 0.3 grams.
These fragments functioned as magnetic recorders, maintaining the magnetic field present when the rocks were formed billions of years ago. The authors subsequently extracted the ancient magnetic signals using highly sensitive laboratory methods.
"When it comes to magnetism, small sample sizes result in weak signals, which demand challenging, thorough lab work," said lead author Cai Shuhui, a colleague of Mitchell's at the Institute of Geology and Geophysics.
They were just good enough.
The magnetic strength of two to four microteslas stood in stark contrast to the much stronger magnetic fields that characterized the moon's early history, which reached tens of microteslas.
The area of the planet's magnetosphere that is covered in a magnetic field is significantly wider than previously assumed.
A magnetic field generated in the Moon's core indicates that its deep interior was still warm and geologically active, which would explain the puzzling volcanic activity observed in the samples returned by the Chang'e-5 mission.
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This article originated in the South China Morning Post (www.scmp.com), a leading news outlet focused on China and Asia.
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