Moon younger than expected?

New dating of lunar rock contradicts conventional theory

Full moon © Luc Viatour / GFDL
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The moon is either significantly younger than assumed or he never owned a magma ocean. This is postulated by an international research team in the journal "Nature". Both would contradict current theory. However, according to the researchers, their study of lunar rocks suggests this conclusion.

According to established theory, the moon was formed when a Mars-sized protoplanet collided with the still young earth. Out of the debris thrown into space, the Earth's moon was formed. At first, a hundred-kilometer-thick ocean of liquid magma covered the young moon. As soon as he froze, the first minerals and rocks of the moon crust were formed. "The earth's moon is the archetypal example of this kind of differentiation, " explain Lars Borg of the Lawrence Livermore National Laboratory in California and his colleagues. This scenario has the great advantage of being able to explain the formation mechanisms of all rocks occurring on the moon.

Common theory does not fit the new dating

However, their studies of lunar rocks have yielded values ​​that are inconsistent with this scenario. The scientists used several methods to determine the age of a rock that is considered to be particularly primitive. This so-called anorthosite is said to date from the time of moon formation. "So far, attempts to date this rock variety, delivered contradictory results, " the researchers write in the journal "Nature". Therefore, they would have improved and expanded the standard methods.

Their dating showed that lunar anorthosity could have been formed only 4.36 billion years ago. This corresponds to a time around 200 million years after the formation of the solar system. So far, scientists had settled the formation of the moon and its first rocks much earlier.

The now measured extremely young age could be due to the fact that the moon solidified significantly later. "This means that the moon solidified relatively slowly after the collision or that it contained enough heat to delay the formation of solid rocks, " say the researchers. display

Regional smelting instead of magma ocean?

But it is also possible that the lunar surface has formed differently than previously thought. The lunar Magamozean did not exist then. Instead, the lunar surface was only partially melted, so the rocks were formed at different times. "This scenario of serial magmatism would have the advantage that it could also explain the older dated moon rock samples, " write Borg and his colleagues.

The big disadvantage, however, is that the theory of a lunar magma ocean is based on strong evidence. Numerous chemical and geological features, as well as isotope distributions of lunar rocks speak for it. If the theory turns out to be wrong, the formation of other rocky planets and moons must also be reconsidered, the researchers write.

However, they do not provide a clear answer to what they believe happened then. They conclude their article with a consideration of the arguments for or against both scenarios. Although they scratch the usual theory, they do not yet offer a watertight alternative. (Nature, 2011; DOI: 10.1038 / nature10328)

(Nature, 18.08.2011 - NPO)