|Why do planets have different layers?
|Question Date: 2013-03-21|
Planets have different layers because
different materials have different densities.
Density is how heavy matter is at a certain
size. The planets formed as dust, gas, asteroids
and comets collided together. We call
this “accretion.” Accretion makes matter very
hot, hot enough to melt most rocks and metal!
While the planets were still hot, the densest
matter (pure metal) sank to the cores and the
lightest matter (gas) floated to the surface.
There are four main materials in the solar
system: metal, rock, water, and gas. Metal is
the densest and so it is at the core of every
planet. Around the metal cores, the planets have
a mantle and crust made of rock. Outside of the
rock is where you find the lightest materials
(least dense), like water and gas. Each planet
is a little different, but remember, it is all
about density! (Ask Scienceline about how the
solar system formed if you want to know more!)
Please look at this interesting picture the
Denser substances fall faster than lighter
substances, and thus settle to the inside of
planets, where the gravity draws it. Lighter
things float on top of the denser material. Air
sits on top of water, water on top of rock, and
rock on top of metal - that's basically the
layering of the Earth. Gas planets have layers,
too, but I don't think we've understood those as
Different materials will settle at different
levels according to their density. For instance,
the interior of the Earth is iron and nickel,
which are solid and dense materials compared to
water. Water, in turn, is dense compared to air,
which is further "out" from the center of the
Earth. I hope this helps!
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