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The Earth and its constant companion, the Moon, have a very similar make-up, something that has long puzzled scientists when it comes to deciding how the satellite planet formed.
One prevailing hypothesis suggests the Moon was formed when it splintered off in a single, giant impact between Earth and another object in the Solar System. In this theory, about a fifth of the Moon’s material would have come from Earth and the rest from the impacting body. Since it was proposed in the 1970s, this has been the go-to explanation for how the Moon was born.
However, the Moon and Earth have far more in common materially than the one-fifth theory dictates, leading scientists to now propose that the Moon was in fact created when a collective of smaller bodies smashed into the Earth. A study describing this theory has been published in Nature Geoscience.
Raluca Rufu, of the Weizmann Institute of Science and co-author of the new study, said: “The multiple impact scenario is a more ‘natural’ way of explaining the formation of the Moon.”
In order to investigate the theory, Rufu and a team of scientists created nearly a thousand computer simulations between a proto-Earth and embryonic planets, named planetesimals. Every collision would have formed a disk of debris around the proto-Earth, which would clump together to form “moonlets” or dwarf moons, made up of the excavated material from Earth. The moonlets would then combine to formulate the Moon, and closely resemble the Earth’s composition.
"In the early stages of the Solar System, impacts were very abundant, therefore it is more natural that several common impactors formed the Moon rather than one special one," Rufu told AFP.
The researchers proposed that about 20 such crashes would have been needed to build the Moon.
Writing in an accompanying comment piece on the study in Nature Geoscience, Imperial College London researcher Gareth S Collins said: “Building the moon in this way takes many millions of years, implying that the Moon’s formation overlapped with a considerable portion of Earth’s growth.” However, he believes more understanding is needed of how the moonlets formed and merged efficiently in order to build the Moon and to fully discard the single-crash theory, saying: “For final adjudication, we must now look to firmer evidence on each side.”
This article was originally published by WIRED UK
