Moon once had own magnetic field: Swiss research

The Moon once had its own magnetic field (study) Keystone-SDA

The Moon once had its own magnetic field, according to Swiss researchers who analysed data collected by probes flying over the far side of the Moon.

The analysis, published on Wednesday in the specialist journal Science Advances, lends support to the theory of a phenomenon known as a ‘geodynamo’ in the Moon’s core.

On Earth, the magnetic field is generated deep within the planet. In the outer core, liquid iron is in constant motion. This movement generates electric currents which, in turn, create the Earth’s magnetic field.

This process is known as a ‘geodynamo’, much like a bicycle dynamo, which converts movement into electrical energy. This magnetic field surrounds the Earth and protects it, in particular, from the charged particles of the solar wind.

Unlike the Earth, the Moon currently has no magnetic field. The question of whether this was different in the past has, until now, been the subject of scientific controversy, writes the Swiss federal technology institute ETH Zurich.

Rock samples collected during the Apollo space missions had provided conflicting evidence.

Conflicting data

For their new study, Swiss researchers did not use rock samples, but rather measurements of gravity and the magnetic field taken by probes orbiting the Moon. The analysis focused on the Dewar region, located on the far side of the Moon.

Using this data, they developed a model of the subsurface structure. According to this model, there is a rocky strata approximately 60km wide and up to 9km deep.

This area is thought to be denser than the surrounding lunar crust and strongly magnetised. Taken together with the geochemical data and topography, this evidence suggests the presence of solidified magma originating from an underground volcanic complex.

Based on the iron content, the researchers estimated that the Moon’s magnetic field was at least 10 microteslas 4.2 billion years ago. This represents between one-fifth and one-third of the current strength of the Earth’s magnetic field, which is approximately 50 microteslas.

The researchers have ruled out the possibility that a massive meteorite impact could have caused this magnetisation.

As the Dewar region is located outside the exposed zones, it is still unclear how the Moon’s relatively small core could have generated such a powerful magnetic field.

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Translated from French, reviewed by an English Department journalist.