Where did the Moon come from? The most widely accepted theory is that the Moon was formed through a collision between the Earth and another planet early on in the Solar System's history. However, a new study from the Weizmann Institute of Science suggests there wasn't one collision, but several.

The commonly accepted origin suggests that the one big collision threw up debris that eventually coalesced and formed the Moon. This theory is supported by chemical analyses of Moon samples, which show them to be pretty much identical to Earth rock.

But in all the Moon samples, there's no trace of that other planetoid that supposedly hit us. If a large body did hit us, there should be traces of that body among the debris that formed the Moon. What the Weizmann scientists propose is that instead of one large body, we were hit by several small ones, and that's why there's little trace of them.

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According to this new hypothesis, multiple impacts with smaller asteroids spread over millions of years kicked up enough debris to form several small moonlets, which eventually merged to make a single moon. The researchers argue that their hypothesis is better supported by the data—or lack thereof.

On the one hand, this theory seems more plausible than the current paradigm. In order for a single large planetoid to form a moon like ours, it would have to be a certain specific size and collide with the Earth at a specific speed and angle. That's a lot of specifics. The multiple-impact theory is much less picky.

However, it's tough to prove a theory based on what the data don't show. The best evidence for the multiple-impact theory is that the Moon shows no evidence of another large body, and that by itself isn't enough to prove anything.

So this mystery endures.

Source: Weizmann Institute of Science

From: Popular Mechanics