The mineral olivine? here an olive tuber from the earth's mantle surrounded by basalt? has been discovered at the edges of impact craters on the moon. It is rock from the moon mantle. Photo: David Köndgen
Read out Rocks from the interior of the moon are exposed on the lunar surface. This was discovered by Japanese researchers after the evaluation of images from the research satellite Kaguya. Especially near impact craters, they identified large amounts of the mineral olivine, which otherwise does not occur on the surface of the moon. The minerals must have been exposed by meteorite hits, because the composition speaks against a volcanic origin. So far, little is known about the processes and the composition of the Moon's interior. The Kaguya spacecraft recorded data over a period of one and a half years from 100 kilometers on the moon: it collected information from about 70 million points, covering an area of ​​0.1 to 0.25 square kilometers. The gauges aboard Kaguya recorded wavelengths at which the samples emitted energy in the form of electromagnetic waves. In the evaluation that has now been carried out, the scientists determine the composition of the elements with a so-called spectral analysis. Conclusion: In the rocks at the edges of numerous impact craters are accumulations of the mineral olivine, which is also the main component of the mantle. The centers of the lunar craters, however, were free of olivine.

So far there are no samples from the moon mantle. The Apollo astronauts and the Soviet robot mission brought only surface rocks to Earth. Also, some meteorites hit on the earth come from the moon. Only certain information about the interior of the moon is available: volcanic eruptions on the moon sometimes brought iron-rich melts to the surface, which can not come from the lunar crust. This is on average seventy kilometers thick? three times as powerful as the earth's crust? and consists mainly of the silica material feldspar. By contrast, the research on the structure of the moon mantle under the crust has so far been in the dark.

According to the study, olivine comes from inside the moon and is a result of crater formation. This is supported by the fact that the crust is significantly thinner at thirty to fifty kilometers in the crater area than anywhere else, write the scientists. Upon impact of a meteorite, most of the crust may have been blown away at the point of impact. Subsequently, the exposed mantle was again covered by lava only inside the crater.

Alternatively, the olivine-rich material could have come from lower depths of the lower crust and ascended in the molten state. However, after a more detailed analysis, the scientists excluded this variant: The composition of the rocks of the crater rim does not match the components of the lower crust. display

Satoru Yamamoto (Center for Global Environmental Research, Ibaraki) et al .: Nature Geoscience, online pre-release, doi: 10.1038 / ngeo897 ddp / David Köndgen


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