Changes

There is not a complete consensus amongst contemporary scientists as to how the Moon came into existence. Historically , three hypotheses were widely seen as plausible contenders for such an explanation: they were the “Fission Hypothesis”, which held that the Moon was ejected by the ancient, swiftly-spinning Earth; the “Capture Hypothesis”, in which the Earth’s gravity captured another planet; and the “Co-accretion Hypothesis” in which both the Earth and the Moon came into being side by side formed together from the same primordial loose aggregation of space dust.  All of these scenarios had serious defects as theories, and all were formulated before the Apollo Moon Program of the late 1960s and early 1970s brought back tons of Moon rock to provide scientists with unprecedented data about the Moon’s composition and history. That data, and the more sophisticated measurements of the Moon’s mass and orbit available to recent researchers, led to the earlier theories losing favor and the promotion of a new one: “The Big Impact Hypothesis”. This theory envisages a massive collision between an ancient Earth and a large asteroid, one in which the early Earth melted and the asteroid disintegrated, only to re-coalesce as the Moon over a period of time.