Does Mars have a continental crust?

Marsrover Curiosity finds unusually quartz-like rocks

Landscape on Mount Sharp: Are there any continental crusts left over here? © NASA / JPL-Caltech / MSSS
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Earth may not be the only planet with a continental crust. Because now the NASA rover Curiosity has also discovered rocks on Mars with unexpectedly high silicon contents. They are similar to terrestrial quartz rocks and could indicate that Mars, at least below the southern highlands, once had a typical continental crust, as researchers report in the journal "Nature Geoscience".

So far, the earth has been considered a nerd among the planets of the solar system, because it is the only one that has two different types of crust - at least that's what you thought. On the one hand, this is the thin but dense oceanic crust, which consists mainly of basalt-like gabbro and is formed along the mid-ocean ridges. Rock crusts of similar composition have been found on other planets, the Martian surface also consists mainly of such basaltic rocks.

Strikingly bright chunks

However, the continental crust has so far only been detected on earth. It forms the base of the landmasses and was created by complex transformation processes in the early days of the planet. It is thicker, less dense and contains more silicon than its oceanic counterpart. But as it turns out, even our cold neighbor Mars could at least in places possess such a continental crust.

Violaine Sautter of the Muséum d'Histoire Naturelle in Paris and her colleagues have analyzed data from the NASA Mars Rover Curiosity for their study. During his drive through the Gale crater, he analyzed 22 strikingly bright rocks using his laser spectrometer. These stones were probably flushed into the crater in the early days of Mars. "Their place of origin is a layer several kilometers thick under the present-day Martian surface, which appears in the northern crater rim, " the researchers explain.

One of the sample lumps, he shows feldspar mixed with quartz crystals and dark mafic rock. © NASA / JPL-Caltech / MSSS

More silicon than thought

The analyzes revealed that these rocks belong to different geochemical types, both of which contain more than 60 percent silicon dioxide but differ in alkalinity. "Our most exciting find are the quartz-like chunks of Group 1, " report Sautter and her colleagues. These rather coarse-grained samples are similar in composition to the continental crustal mass of the earth. display

Theoretically, these rocks could represent a local peculiarity, which originated, for example, when molten rock from deeper layers rose to the surface. "Such quartz-feldspar-like material was discovered by orbiters already in other regions of Mars, " said the researchers. Among other crater mountains in the north of the Syrtis Major region and on the edge of the Antoniadi crater.

Highlands as a continental crust residue?

"This geographically widely distributed evidence could therefore be the result of widespread silicon-rich rocks, " the researchers speculate. In their view, it is quite likely that these single finds are remnants of an ancient continental crust of Mars. It might still be common among the Martian highlands of the south.

This false-color image of the Marstopografie shows it clearly: The planet has two very different Hemisph ren: the northern one is deeper, in the south donkiert the highland. NASA / JPL-Caltech

The results of gravity field measurements may also support this hypothesis. Because they indicate that the crust of the Martian highlands could be less dense than in other areas and also less dense than analyzes of Martian meteorites so far suggested. "This paradox could be explained by a 'buried' lighter component in the southern hemisphere, " says Sautter and her colleagues.

The data are still insufficient to support this hypothesis. But if this were confirmed, the Earth would no longer be the only planet in the solar system with a continental crust. Mars and Earth would then be much more similar to their earlier geological history than previously thought, as the researchers emphasize. (Nature Geoscience, 2015; doi: 10.1038 / ngeo2474)

(Nature, 14.07.2015 - NPO)