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WASHINGTON, Jan. 10 (Xinhua) -- The moon may have formed from a series of large impacts on the ancient Earth instead of a single giant collision, according to a study published in the journal Nature Geoscience on Monday.
This model contradicts the prevailing hypothesis that the moon was born from a single giant collision between Earth and a Mars-sized celestial body.
In the single impact scenario, the Mars-sized body collided with the Earth, sending trillions of tons of debris of the embryonic Earth into space. Gravity bound the ejected particles together, creating the moon.
However, the single impact scenario failed to explain why the makeup of the moon are near identical to the Earth, rather than a mix of Earth and another planet.
In a successful giant-impact scenario, either most of the material that forms the moon comes from the Earth, or the impactor's composition is identical to the Earth. "However, both are possible, but unlikely, scenarios," the study said.
"The multiple impact scenario is a more 'natural' way of explaining the formation of the Moon," Raluca Rufu of the Weizmann Institute of Science in Israel, co-author of the study, was quoted by the AFP as saying.
Such multiple hits would have kicked up more Earth material than a single one into the Earth's orbit to form moonlets that closely resemble the Earth's composition, the researchers said.
"It would take about 20 of these moonlet-forming collisions to assemble the Moon," the study said.
Rufu and his team conducted a series of computer simulations of moon-to-Mars sized celestial bodies impacting the proto-Earth. After each impact, the debris formed disks around the Earth like Saturn's rings. Over centuries, debris in several disks accreted to form moonlets that eventually migrated outwards and merged to form one big moon.
"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 the AFP.
A moon assembled through multiple impacts implies that the moon was formed over many millions of years, rather than in a geologic instant, the study said.
The Earth and moon's interiors may be less well mixed than in a giant-impact scenario, potentially preserving a record of this period of bombardment, it added.
