Nasa’s Apollo missions returned a wealth of lunar rock samples to Earth, providing invaluable insights into the Moon’s geological history. Despite significant advancements in lunar studies over the decades, one intriguing question persists: how did certain moon rocks acquire magnetic properties when the Moon currently lacks a magnetic field similar to Earth’s?
Researchers have proposed several theories to unravel this scientific enigma. In a new study published in the journal Science Advances, scientists from the Massachusetts Institute of Technology (MIT) present the hypothesis that a large asteroid impact may have temporarily intensified the Moon’s weak magnetic field during its early history, leaving a magnetic imprint on some of the lunar samples.
Findings from ongoing spacecraft missions, including data from China’s Chang’e 5 and Chang’e 6, have hinted at the possibility of an early, albeit weak, magnetic field existing on the Moon. These findings raise the question of the origin of such a magnetic field. Typically, magnetic fields in celestial bodies arise from a dynamo effect, where convecting molten metals in the core generate magnetic forces. However, the early Moon’s small core was closely matched in temperature to its mantle, which likely inhibited sufficient convection for a robust dynamo.
Several explanations have emerged regarding the development of a core dynamo on the Moon. A 2022 study suggested that during the Moon’s formative years, when its surface was molten, large rocks coalesced as magma cooled and solidified. In this scenario, denser minerals would sink toward the core, while lighter ones formed an upper crust.
The authors of this analysis argued that a layer of titanium crystallized beneath the lunar surface, eventually breaking apart into smaller masses that descended through the mantle. This gravitational overturn could have generated convection due to the temperature differences between the sinking materials and the hotter core, resulting in the intermittent creation of magnetic fields. This theory offers a potential explanation for the magnetic characteristics observed in some moon rocks.
Alternatively, some researchers argue that the evidence may not necessitate a dynamo-driven magnetic field at all. A 2021 study posited that previous analyses of lunar samples could have been altered during examination. In this research, the team re-evaluated Apollo 16 samples from 1972 using CO2 lasers to heat the rocks, mitigating the risk of altering their magnetic carriers. Their findings suggested that the magnetic signatures could be attributed to impacts from meteorites or comets intersecting the Moon’s surface.
