For more than a century, scientists discussed how the earth's moon formed. But researchers in Yale and Japan say they may have the answer.
Many theorists believe that an object the size of Mars struck the primitive Earth, and the material dislodged from that collision formed the base of the moon. When this idea was tested in computer simulations, it was discovered that the moon would be made primarily from the impacting object. However, the opposite is true; We know, by analyzing the rocks brought back from the Apollo missions, that the Moon consists primarily of Earth material.
A new study published April 29 in Nature Geoscience, co-authored by geophysicist Shun-ichiro Karato of Yale, offers an explanation.
The key, says Karato, is that the primitive proto-Earth – about 50 million years after the formation of the Sun – was covered by a sea of hot magma, while the impacting object was probably made of solid material. Karato and his collaborators began testing a new model, based on the collision of a proto Earth covered by an ocean of magma and a solid impacting object.
The model showed that after the collision, the magma is heated much more than the impacting object's solids. The magma expands in volume and enters orbit to form the moon, the researchers say. This explains why there is much more Earth stuff in the moon makeup. The previous models did not take into account the different degrees of heating between the proto-earth silicate and the impactor.
"In our model, about 80% of the moon is made of proto-terrain materials," said Karato, who conducted extensive research on the chemical properties of proto-terrestrial magma. "In most previous models, about 80% of the moon is made of the impactor. This is a big difference."
Karato said the new model confirms earlier theories about how the moon formed, without the need to propose unconventional collision conditions – something the theorists have had to do so far.
For the study, Karato conducted research on the compression of the molten silicate. A group from the Tokyo Institute of Technology and the RIKEN Center for Computational Science developed a computational model to predict how the collision material became the moon.
The first author of the study is Natsuki Hosono from RIKEN. Other co-authors are Junichiro Makino and Takayuki Saitoh.
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