The mystery of the magnetic field of the Moon

I have learned that the Moon is a rather mysterious object. The origin of the Moon is a mystery although the fact that its composition is the same as that of Earth gives hints; it seems that the Moon has effectively turned inside out; the faces of the Moon are very different; the latest mystery that I learned of, are the magnetic anomalies of the Moon. The TGD based view of the origin of the Moon combined with the TGD view of magnetic fields generalizing the Maxwellian view explains all these mysterious looking findings.

The magnetic field of the Moon (see the Wikipedia article) is mysterious. There are two ScienceAlert articles about the topic (see this and this). There is an article by Krawzynksi et al with the title “Possibility of Lunar Crustal Magnatism Producing Strong Crustal Magnetism” to be referred as Ketal (see this). The article by Hemingway and Tikoo with the title “Lunar Swirl Morphology Constrains the Geometry, Magnetization, and Origins of Lunar Magnetic Anomalies” to be referred as HT (see this) considers a model for the origin local magnetic anomalies of the Moon manifesting themselves as lunar swirls.

1. The magnetic anomalies of the Moon

1. The Moon has no global magnetic field but there are local rather strong magnetic fields. What puts bells ringing is that their ancient strengths according to HT are of the same order of magnitude as the strength of the Earth’s magnetic field with a nominal value of B_E≈ .5 Gauss. Note that also Mars lacks long range magnetic field but has similar local anomalies so that Martian auroras are possible. The mechanism causing these fields might be the same.
2. The crustal fields are a surface phenomenon and it is implausible that they could be caused by the rotation of plasma in the core of the Moon. The crustal magnetic fields seem to be associated with the lunar swirls, which are light-colored and therefore reflecting regions observed already at the 16^th century. Reiner Gamma is a classical example of a lunar swirl illustrated by Fig 1. of this. The origin of the swirlds is a mystery and several mechanisms have been proposed besides the crustal magnetism.
3. Since Moon does not have a global magnetic field shielding it from the solar wind and cosmic rays, weathering is expected to occur and change the chemistry of the surface so that it becomes dark colored and ceases to be reflective. In lunar maria this darkening has been indeed observed. The lunar swirls are an exception and a possible explanation is that they involve a relatively strong local magnetic field, which does the same as the magnetic field of Earth, and shields them from the weathering effects. It is known that the swirls are accompanied by magnetic fields much stronger than might be expected. What is interesting is that the opposite face of the Moon is mostly light-colored. Does this mean that there is a global magnetic field taking care of the shielding.

The article HT discusses a mechanism for how exceptionally strong magnetization could be associated with the vertical lava tubes and what are called dikes. The name indicates that the dikes are parallel to the surface.

1. The radar evidence indicates that the surface of the Moon once contained a molten rock. This suggest a period of high temperature and volcanic activity billions of years ago. Using a model of lava cooling rates Krawczynski and his colleagues have examined how a titanium-iron oxide, a mineral known as ilmenite – abundant on the Moon and commonly found in volcanic rock – could have produced a magnetization. Their experiments demonstrate that under the right conditions, the slow cooling of ilmenite can stimulate grains of metallic iron and iron nickel alloys within the Moon’s crust and upper mantle to produce a powerful magnetic field explaining the swirls.
2. The paleomagnetic analysis of the Apollo samples suggests that there was a global magnetic field during period ≈ 3.85-3.56 Ga (the conjectured Theia event would have occurred ≈ 4.5 Ga ago), which would have reached intensities .78+/- .43 Gauss. The order of magnitude for this field is the same as that for the Earth’s recent magnetic field. At the landing site of Apollo 16 magnetic fields as strong as .327 × 10^-3 Gauss were detected. A further analysis suggests the possibility of crustal fields of order 10^-2 Gauss to be compared with the Earth’s magnetic field of .5 Gauss.
3. The lunar swirls consist of bright and dark surface markings alternating in a scale of 1-5 km. If their origin is magnetic, also the crustal magnetic fields must vary in the same scale. The associated source structures, modellable as magnetic dipoles, should have the same length scale. The restricted volume of the source bodies should imply strong magnetization. 300 nT crustal fields (.3 × 10^-2 Gauss) are necessary to produce the swirl markings. The required rock magnetization would be higher than .5 A/m (note that 1 A/m corresponds to about 1.25× 10^-2 Gauss).

The model assumes that below the surface there are vertical magnetic dipoles serving as sources of the local magnetic field. The swirls as light regions would be above the dipoles generating a vertical magnetic field. In the dark regions, the magnetic field would be weak and approximately tangential due the absence of magnetization.

The above picture would conform with the TGD based model in which the face of the Moon opposite to us corresponds to the bottom of the ancient Earth’s crust. It could have been at high enough temperature at the time of the explosion producing the Moon. The volcanic activity would have occurred in the Earth’s crust and magnetization would be inherited from that period.

One can however wonder how the magnetized structures could have survived for such a long time. The magnetic fields generated by macroscopic currents in the core are unstable and their maintenance in the standard electrodynamics is a mystery to which TGD suggests a solution in terms of the monopole flux contribution of about 2B_E/5 to the Earth’s magnetic field which is topologically stable (see this). If the TGD explanation for the origin of the Moon is correct, these stable monopole fluxes assignable with the ancient crust of the Earth should be present also in the recent Moon and could cause a strong magnetization.

The mysterious findings could be indeed understood in the TGD based model for the birth of the Moon as being due to an explosion throwing out the crust of Earth as a spherical shell which condensed to form the Moon.

1. The TGD based model for the magnetic field of the Earth (see this) predicts that the Earth’s magnetic field is the sum of a Maxwellian contribution and monopole contribution, which is topologically stable. This part corresponds to monopole flux tubes reflecting the nontrivial topology of CP₂. The monopole flux tubes have a closed 2-surface as a cross section and, unlike ordinary Maxwellian magnetic fields, the monopole part requires no currents to generate it. This explains why the Earth’s magnetic field is stable in conflict with prediction that it should decay rather rapidly. Also an explanation for magnetic fields in cosmic scales emerges.
2. The Moon’s magnetic field is known to be a surface phenomenon and very probably does originate from the rotation of the Moon’s core as the Earth’s magnetic field is believed to originate. In TGD, the stable monopole part would induce the flow of charged matter generating Maxwellian magnetic field and magnetization would also take place.

If the Moon was born in the explosion throwing out the crust of Earth, the recent magnetic field should correspond to the part of the Earth’s magnetic field associated with the monopole magnetic flux tubes in the crust. The flux tubes must be closed, which suggests that the loops run along the outer boundaries of the crust somewhat like dipole flux and return back along the inner boundaries of the crust. Therefore they formed a magnetic bubble. I have proposed that the explosions of magnetic bubbles of this kind generated in the explosions of the Sun gave rise to the planets (see this and this).

If the mass density was not changed appreciably the spherical shell had to transform to a folded structure filling the volume of the Moon. The flux tubes and crust formed a structure analogous to a cloth pack. The contracting spherical disk would have folded in the volume of Moon in a spherically symmetric way along the monopole flux tubes of a folded structure consisting of spherical layers. One could image the Moon as a deformation of a cube consisting of parallel layers to form a ball. There would be a symmetry axis, which could correspond to the rotation axis. Reconnections would have split the long closed monopole flux tubes to shorter ones unless this happened already in the explosion.

This idealization predicts that the Moon has a layered structure of about 27 layers and magnetic layering by monopole flux tubes. The magnitude of the dark monopole flux for Earth is about B_M =2B_E/5 ≈ .2 Gauss for the nominal value B_E=.5 Gauss. The monopole flux for the long loops is tangential but if reconnection occurs there are portions with length Δ R inside which the flux is vertical and connects the upper and lower boundaries of the layer. Note that in the TGD inspired quantum hydrodynamics also dark Z⁰ magnetic fields associated with hydrodynamic flows are possible and could be important in superfluidity (see this).

For a summary of earlier postings see Latest progress in TGD.

For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.