Sonia Tikoo on the Moon’s Magnetic Field
For quite some time we have known that the Moon had a strong magnetic field between about 4.25 and 3.5 billion years ago. In the past few years, we have discovered that a weaker field was operating as recently as about 1 billion years ago. After that, the Moon’s magnetic field vanished entirely. In the podcast, Sonia Tikoo explains that we don’t fully understand either how the early field could be so strong, or how any field could last so long. Certainly, no single mechanism can explain both the high-field early epoch and the long weak-field tail.
Sonia Tikoo studies the history of magnetic fields on the Moon and other small solar system bodies using paleomagnetism and fundamental rock magnetism. She is an Assistant Professor in the Department of Geophysics at Stanford University.
Podcast Illustrations
The Moon is much smaller than the Earth, and its core occupies a smaller fraction of the Moon’s volume than that of the Earth. As Tikoo explains in the podcast, the scaling laws that apply to the magnetic field strength generated by core-driven convection suggest that the Moon’s magnetic field should be a fraction of a microtesla (μT). Instead, rock samples returned from the Moon indicate a much stronger field of 20 - 100 μT 4.5 to 3.5 billion years ago.
Plot showing current experimental estimates of the intensity of the lunar magnetic field over time.
Courtesy of Ji-in Jung
Lunar crustal field map showing total field strength at 30 km altitude.
Wieczorek et al., 2023 (need full citation)
Lunar surface shots of Reiner Gamma swirl/magnetic anomaly
NASA/LRO WAC Science team