Speaker 1: Welcome to brain Stuff from house stuff Works dot com
Speaker 1: where smart Happens. I am Marshall Brain with today's question,
Speaker 1: where did the Moon come from? This question became famous
Speaker 1: because of Bill O'Reilly, but it's a classic house stuff
Speaker 1: Works kind of question, so let's take a look at it.
Speaker 1: It's a basic tenet of science that everything in nature
Speaker 1: has some kind of explanation. So therefore, the moon has
Speaker 1: to have some kind of explanation. It had to come
Speaker 1: from somewhere or something. And scientists have been thinking about
Speaker 1: this and pondering this for a long time. They've come
Speaker 1: up with a number of theories that didn't really work
Speaker 1: when they looked at them deeper. So one example would
Speaker 1: be that the Earth and the Moon formed together when
Speaker 1: the Solar System was forming, there was an accretion process
Speaker 1: that allowed dust to accumulate into planets, and perhaps the
Speaker 1: Moon formed in the same way the Earth formed, and
Speaker 1: they formed next to each other and became this kind
Speaker 1: of orbiting system. There's a couple of reasons why we
Speaker 1: can say that isn't the case, but one really good
Speaker 1: reason is the fact that the Moon and the Earth
Speaker 1: have different compositions. The amount of iron in the cores
Speaker 1: of these two planets is remarkably different. If they had
Speaker 1: formed together, you'd expect them to be the same, So that,
Speaker 1: along with other things, kind of rules that out. Another
Speaker 1: theory that scientists came up with was the centrifugal force idea,
Speaker 1: the idea that the Earth formed with the Solar System,
Speaker 1: and it was much bigger than it is today, and
Speaker 1: it was spinning extremely quickly, and a chunk of it
Speaker 1: in the molten state just kind of flung off as
Speaker 1: a blob, and that became the Moon. So scientists looked
Speaker 1: at that and they thought about it, and they modeled
Speaker 1: it with computers. And there's a couple of problems with
Speaker 1: that theory, the main one being that the Earth would
Speaker 1: have to be spinning way too fast for it to
Speaker 1: fling a chunk of itself off, and it if it
Speaker 1: had been spinning that fast when the Moon was formed,
Speaker 1: then it would be spinning much faster than it is today.
Speaker 1: A day wouldn't be twenty four hours long, it would
Speaker 1: be much much shorter. Another theory is some kind of
Speaker 1: asteroid capture event. So an asteroid comes by and it
Speaker 1: somehow gets caught in Earth's gravitational field and it becomes
Speaker 1: our moon. The problem with this theory is that there
Speaker 1: would have to be something that would break the asteroid
Speaker 1: or slow it down once it approached Earth, and the
Speaker 1: atmosphere is one thing that could have done that. But
Speaker 1: because of the size of the Moon and the thickness
Speaker 1: of Earth's atmosphere and a couple other things, that theory
Speaker 1: doesn't really work very well either. But it probably is
Speaker 1: what happened with the little moons that are surrounding Mars
Speaker 1: right now. A fourth theory is the one that most
Speaker 1: scientists are currently pretty comfortable with, and the basic idea
Speaker 1: here is pretty easily stated. A planet like object with
Speaker 1: a size roughly equal to Mars hit planet or shortly
Speaker 1: after these two bodies formed, you know, maybe fifty million
Speaker 1: years after these two bodies formed, and the Moon was
Speaker 1: formed by matter that was ejected into orbit by that collision.
Speaker 1: So it would have been a massive collision with a
Speaker 1: lot of energy, and these objects would have formed into
Speaker 1: another molten ball in a chunk just was blasted out
Speaker 1: into orbit, and it would have been blasted out into orbit.
Speaker 1: Probably is is bits and pieces that would have formed
Speaker 1: or aggregated together to create the Moon that we have today.
Speaker 1: Science is based on evidence. So what evidence do we
Speaker 1: have to support this view of the Moon's origin. One
Speaker 1: piece of evidence came back from the Apollo Moon missions.
Speaker 1: The moon rocks collected by the Apollo astronauts support this theory.
Speaker 1: Another thing that support is the size of the core
Speaker 1: of the Moon. Is mentioned earlier. The core of the Moon,
Speaker 1: being of iron, is much smaller than the core of
Speaker 1: the Earth, and that fact is easily explained by some
Speaker 1: kind of collision event. In that event, mostly mantle would
Speaker 1: have been ejected into the uh into orbit around Earth
Speaker 1: rather than the iron core, it's thought, and so the
Speaker 1: Moon would therefore have less iron in its core as
Speaker 1: a result. Another piece of evidence is the canting of
Speaker 1: the Earth's rotational axis. You know, the fact that the
Speaker 1: axis is tilted, and this is what gives us our
Speaker 1: seasons and the length of the Earth day. And another
Speaker 1: is the distance of the Moon from the Earth and
Speaker 1: the increase in that distance over time. So you take
Speaker 1: pieces of evidence like this and they work together with
Speaker 1: each other to support the theory that the Moon was
Speaker 1: created by a collision event. There's a great deal of
Speaker 1: cheerill available through Google if you'd like to increase your
Speaker 1: scientific understanding of the Moon's origin. It really is an
Speaker 1: interesting question. If you think about it and you know
Speaker 1: in theory, you could come up with another idea for
Speaker 1: where the moon came from, and if you have the evidence,
Speaker 1: you could bring it forward and create another scientific discovery.
Speaker 1: That's How Science Works. Be sure to check out our
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