Theories on the formation of Moon had been a puzzle for scientists. Now, another theory affirms that moon was formed from the merger of many small moonlets, which were actually splinters of debris that emanated from multiple asteroid collisions with Earth.
The new theory, mooted by researchers from the Technion-Israel Institute of Technology and the Weizmann Institute of Science, is significant for its questioning of the long-held "giant impact" theory. The reigning theory claims that a giant asteroid hit the Earth and the resulting debris led to the formation of the Moon.
That assumption was getting weaker after the analysis of Moon rock brought by astronauts. It showed that the rocks were closely identical to those on Earth in terms of composition and there was no trace of the impacting asteroid on the rocks.
During the study, the authors ran 800 simulations of impacts to recreate the conditions that created moonlets. This drove them to conclude that the multiple-impact scenario is more logical in explaining why Moon has an almost identical composition as Earth.
The study, which was conducted by professor Hagai Perets of the Technion-Israel together with professors Raluca Rufu and Oded Aharonson from Weizmann, made a departure from the single collision theory on the lunar formation.
"Our model suggests that the ancient Earth once hosted a series of moons, each one formed from a different collision with the proto-Earth," said co-author Perets.
Merger Of Moonlets
The new theory implies that there could have been many previous moons for Earth and such a Moon would have already existed when the Moon-forming impacts on Earth took place.
The study asserts that an average 20 asteroids might have hit the Earth and the scattered debris on the orbit formed disks around the Earth just like the rings of Saturn. Later on, the debris in many disks conjoined to form moonlets.
Over the centuries, these moonlets moved away from the Earth because of tidal interactions and settled at the Hill radius and over the centuries they merged into a single big Moon.
"The multiple-impact scenario is a more natural way of explaining the formation of the Moon," observed Rufu, the lead author of the study. "A long series of such moon-moon collisions could gradually build up a bigger moon - the Moon we see today," he added.
According to observers, the new theory resonates well with the "Giant Impact Hypothesis" which says Theia, a planet-size rock, struck the Earth and the debris became the Moon.
Hailing the new theory, Gareth Collins, a planetary scientist in London said the study must be credited for reviving "the hitherto largely discarded scenario that a series of smaller and more common impacts, rather than a single giant punch, formed the Moon."
The findings were published in Nature Geoscience.