The new research published by NASA reveals that the heat produced during the crystallization of the lunar core may have developed its now-defunct magnetic field some 3 billion years ago.
Crystallization of the Core of the Ancient Moon:
The moon does not own a magnetic field. However, during the Apollo missions, our Earth received magnetized lunar rocks. So, the astronomers believed that the moon once had its magnetic field. The magnetic field of the moon was as strong as the magnetic field generated by the modern Earth.
They also supposed that the magnetic field of the moon lasted for more than a billion years. This magnetic field was powered by a lunar dynamo. Which is a molten, churning core present at the center of the moon. However, at that time, the astronomers were not able to understand how the moon generated its magnetic field.
Recently, the scientists from the NASA’s Astromaterials Research and Exploration Science (ARES) Division published their research about the crystallization of the lunar core. They worked on different physical and chemical constraints to understand how the moon acquired a magnetic field and maintained it.
Formation of the Magnetic Field of the Moon:
According to the latest research, the moon likely had an iron or nickel core with only a small amount of carbon and sulfur. Due to which, the lunar core had a high melting point. As a result, the crystallization of the lunar core occurred due to which the magnetic field of the moon generated. Consequently, the scientists discovered the magnetic field which was recorded in the ancient lunar samples.
The researchers created different synthetic core compositions based on the recent geochemical data obtained from the moon. Then they equilibrated them at the temperatures and pressures of the lunar interior. According to their estimation, the magnetic field recorded in the lunar samples was as young as 3.1 billion years old. However, it is currently inactive. This indicates that at some point in 3.1 billion years, the heat flow declined to such an extent that the lunar dynamo became inactive.
Up till now, the scientists used to think that the lunar core is composed of a solid inner and liquid outer core on the basis of the Apollo seismic and other geophysical and spacecraft data. However, the ARES group proposed a new specific lunar core composition. It would be partially solid and partially liquid while keeping it consistent with the geophysical and seismic data.
The ARES scientists analyzed the latest Apollo samples for the preparation of iron powder, nickel powder, sulfur powder, and carbon powder. They prepared the powders based on the geochemical proportion estimates of the moon. After preparing the powders, they encapsulated them and heated under pressures corresponding to the pressures inside the lunar interior. They also investigated a wide range of temperatures because the moon might have experienced a drastic change in temperatures from high temperatures to lower ones.
This research has opened new aspects of the geochemically-derived composition of the lunar core and the crystallization of the moon. Before this, the dilemma was that the modelling of the moon involved an iron/nickel core with a high quantity of sulfur contents. Due to which, the melting point of the lunar core was so low that the crystallization would not have occurred.
Therefore, the scientists were not clear about the source of the heat flow out of the lunar core which was required to drive a dynamo. So, they used to propose various sources in their researches like heat from the impact or shear forces. The ARES scientists acknowledge that such sources may be real. However, if the heat from the crystallization of the outer core is available, then it must be the source for the lunar dynamo.