The moon is quite well researched – but there are still mysteries that drive research. One of them now seems to have been resolved.
Nice – The Moon is Earth's closest neighbor and the only alien celestial body that humans have visited so far. Nevertheless, it still poses many mysteries – for example, research is puzzling over how the interior of the moon is structured. Does the Earth's satellite have a half-molten core or is there also a solid inner core in it? This question was unanswered for a long time. But now a research team has clear evidence that there is a solid inner core in the moon.
To study the interior of the moon, researchers use the same methods that they use to study the Earth's interior: seismic waves. The manned "Apollo" missions of the US space agency Nasa have left behind a seismometer on the moon, among other things, whose data show that the core of the Earth's satellite could be at least partially liquid. However, the data is too imprecise to allow more precise conclusions to be drawn about the interior of the moon.
The Moon is Earth's closest neighbour – and yet it still holds many mysteries. © Anthony Anex/dpa
New study: How the moon is built up in its interior
A research team led by astronomer Arthur Briaud (Université Côte d'Azur) has used data from space missions and geophysical measurements to find out more about the interior of the Earth's satellite. The study was published in the journal Nature. The research group uses different computer models of the lunar core to find out which scenario comes closest to the observed data. "Our results (...) prove the existence of an inner core," the research group writes in it.
In their study, the researchers show that the Moon not only has a solid inner core – the structure of the Moon is apparently also similar to that of the Earth. The outer, semi-liquid core therefore has a radius of about 362 kilometers. Inside is the solid inner core, which has a radius of about 258 kilometers. According to the calculations, the inner core has a density of 7822 kilograms per cubic meter – which is roughly equivalent to the density of iron. The outer, semi-liquid core has a lower density of 5025 kilograms per cubic meter.
The Moon has a solid inner core – just like the Earth
The calculations of Briaud's team confirm an earlier research work that processed the "Apollo" measurement data using current seismological methods and also concluded that there was a solid inner core. "The existence of a solid inner core is crucial for understanding the mechanism that leads to the appearance of a planetary magnetic field or not," the research group writes in the study.
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By studying lunar rocks, researchers know that the moon had a strong magnetic field about four billion years ago, which disappeared about 3.2 billion years ago. Such a magnetic field is created by motion and convection in the nucleus – so by knowing the nature of the moon's core, research in the future will be able to explain how and why the magnetic field has disappeared. (tab)