SPACE.com -- 24 Hours of Chaos: The Day The Moon Was MadeFor 25 years, scientists have pondered a theory that the Moon was created when an object the size of Mars crashed into Earth less than 100 million years after the Sun was born, some 4.6 billion years ago. The general idea has been run through the paces and massaged into shape and is now the favored explanation.
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But attempts to model cousins of that theory on computers generate inexplicable side effects.
In one of two leading computer models, Earth was creamed while it was still gathering mass, during a brief time when it was only half its current size. All the rocky inner planets are thought to have formed this way, a method rapid accumulation of matter called
runaway growth.
But if the Moon was carved out during Earth's growth phase, then it would have been around when Earth continued bulking up by swallowing tremendous numbers of large asteroids. Some of these iron-rich rocks would have hit the Moon, too. Yet the iron is not there.
In the other model, the aggressor was three times as massive as Mars and created an excess of rotation in the Earth-Moon system that simply doesn't exist today.
Now researchers have harnessed the latest in computing power to provide the most detailed model ever made of the cosmic scene that supposedly created the Moon. The result, a 3-D animation of the blast and subsequent chaos, is comforting. It shows that the Moon could have formed when a Mars-sized object hit a fully formed Earth.
The collision would have given Earth its spin, defined what we now call an equator, and put enough material into orbit at the right distance from Earth to allow the formation of a satellite that generations would later swoon over.
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