Scientists believe that our moon formed some 4.5 billion years ago when a Mars-sized rocky object, referred to as a protoplanet called Theia, crashed into the young earth. This collision threw debris from both the earth and the protoplanet into the orbit. Eventually some of the debris stuck together to form our moon.
However, many astronomers doubt if Theia ever existed. Their reasoning is that if Theia’s and Earth’s materials combined to form the moon, the moon should be a hybrid of these two. But the chemical composition of moon and earth are precisely the same. This suggests that the earlier belief about moon’s formation has something wrong in it.
A new hypothesis by the Weizmann Institute of Science in Rehovot, Israel, says that the moon-forming scenario is best justified by multiple impacts. According to it, a number of small collisions flung earth’s material into the orbit. These eventually combined to form our moon. The rubble thrown by the initial impact circled the earth. The material, over centuries, bound together into a mini-moon. Later, over many impacts and tens of millions of years, about 20 moonlets intermingled to form a single big moon.