Ancient volcanic slopes cover the high northern latitudes of Mercury. Ghostly are some craters that are covered by the lava flows. (c) NASA / JHUAPL / CIW-DTM / GSFC / MIT / Brown University. Rendering by James Dickson and Jim Head
Read aloud The planet Mercury has always been an outsider among the solid rock planets. After a year in orbit, the data of the spacecraft Messenger now show that the small celestial body is even more exotic than previously thought. Two research teams report in a journal article and at a conference that Mercury's coat contains a layer of iron sulfide? a material that is unlikely to be found in any other planet. In the outer rock hull, however, virtually no iron can be found. Crust and coat are only as thin as the shell of an orange compared to the core. The fact that Mercury has a comparatively large core was already known to planetary researchers because of its high density. The Messenger data now prove that the core fills an even larger part of the planet than they had previously assumed. The radius of the core is about 85 percent of the planet's radius. By comparison, the radius of the Earth's core is half the Earth's radius. Unusual is also the chemical composition of Mercury's core, which probably consists of a liquid outer layer and a solid inner part, as in the case of Earth. According to the researchers, the core of Mercury contains both silicon and large amounts of sulfur as an admixture. Since these substances are not miscible in all pressure and temperature conditions, the researchers conclude that they have a solid iron sulfide layer above the liquid core.

Messenger has now also made an accurate topographic map of the surface and measured the gravity field. As the researchers report, the differences in altitude on Mercury are less than on the moon or the planet Mars. In the huge Caloris Basin, one of the solar system's largest meteorite craters, the crater floor is sometimes higher than the rim. An unknown process must have pushed up the crater floor after its formation. This suggests, according to the researchers, that Mercury's geological activity lasted longer than expected. "So far, many researchers have assumed that Mercury was a dead planet for most of its history, " says Maria Zuber of the Massachusetts Institute of Technology, one of the authors. "Now we see convincing evidence of unusual dynamics within Mercury."

In the dark craters on the poles of Mercury, planetary scientists have been suspecting deposits of ice for some time. Messenger radar measurements now argue that there may actually be ice in the eternal shadow. They identified materials that reflect radio waves perfectly. Whether it is really about water ice, could soon show measurements with the neutron spectrometer of Messenger.

David Smith (Massachusetts Institute of Technology) et al: Science, Online Preliminary Publication, doi: 10.1126 / science.1218809 Maria Zuber (Massachusetts Institute of Technology) et al: Science, Online Preliminary Publication, doi: 10.1126 / science.1218805 science. de - Ute Kehse advertisement

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