| How was the moon created?|
|Question Date: 2012-09-25|
Great question! This is one of my favorite
topics. The moon is actually “closer to home”
than most people think, in fact a lot of the
moon is made up of material that used to be on
earth! The earth formed about 4.56 billion years
ago (that’s a really long time). In the first
several hundred million years of earth’s life it
was getting hit really hard by asteroids,
comets, and meteorites. Impacts
of “planetesimals” (small planets) happened very
often. At 4.5 billion years ago, a planetesimal
the size of Mars crashed into the earth. It hit
the earth with so much energy that part of the
earth was actually broken off and sent into
space. The part that was ripped off was caught
by the gravity of the earth that was left
behind, so it started to orbit it. That is why
the moon orbits the earth. So, the moon is made
up of stuff that was once part of this planet.
In fact, the rocks that we find on the moon are
very similar to rocks that we find in certain
places on earth!
found great information for you on the Web.
Please read it and try to watch the second video
on the web page; it shows a simulation of the
formation of the Moon.
The moon was formed ~4.5 billion years ago,
about 30–50 million years after the origin of
the Solar System, out of debris thrown into
orbit by a massive collision between a smaller
proto-Earth and another planetoid, about the
size of Mars. Initially the Moon spun much
faster, but because it is not perfectly
spherical and bulges out slightly at its
equator, the orbit slowed down and eventually
became tidally locked — keeping the same face
toward the Earth. Bulges along the Earth-Moon
line caused a torque, slowing the Moon spin,
much the same way a figure skater gradually
opens to decelerate a spin. When the Moon’s spin
slowed enough to match its orbital rate, the
bulge was in line with Earth, which is why we
always see the same side of the Moon. In our
solar system, almost all moons spin at the same
rate as they orbit.
The Earth would be a very different place if
the moon did not exist. Not only did the Earth
slow down the Moon’s rotation, but the Moon is
slowing down the rotation rate of the Earth.
Since the moon’s formation, the Earth has been
slowing its rotation due to the friction of the
tides caused by the moon, and in reaction to
this exchange of energy, the moon has been
moving farther away from the Earth. In fact, at
the time of the moon’s formation the Earth
rotated much faster than it does today; a day on
early Earth was only a few hours long. But the
Moon, being small in relation to Earth, will
take more than twice the age of the solar system
to slow Earth’s spin rate to the Moon’s orbital
The most accepted theory is that while the
Earth and Solar System were forming, a large
object (about the size of Mars) crashed into the
Earth at a slow speed, and small angle (it
barely hit us!), knocking some of Earth's mass
off. This mass did not go far enough to leave
Earth's gravitational pull, but far enough to
leave the atmosphere, creating the Moon we know
today. It is also hypothesized that this crash
is responsible for our tilt leading to seasons
as we travel around the sun.
About 4.5 billion years ago, when the Earth
young, an object about the size of Mars collided
with Earth. This collision blasted off a large
amount of material from the outer part of the
Earth and into orbit around the Earth. This
material then coalesced to form the Moon.
Good question - until recently, it was
that the Earth was hit by a Mars-sized object
about 4.5 billion years ago, and that the debris
blown off from the impact is what formed the
moon. I think that theory has come under fire,
though, and I don't know what the current
preferred theory is.
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