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THE INNER PLANETS
• The four planets that are closest to the sun are
called the inner planets.
• They are all small and rocky.
• They are sometimes called the terrestrial planets.
The inner planets: note the spin
and axis angles of each planet
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Earth
• The Earth has an atmosphere that extends for
about 100 kilometers.
• It is 20% oxygen,78% nitrogen and a few other
gases.
• 70% of the surface is covered with water.
• Earth has three main layers, a crust, a mantle,
and a core.
• The crust is the hard rocky surface.
• The mantle is under the crust and is made of
liquid rock.
The Earth as
seen from the
moon
The Earth
The inner core is most likely solid iron and nickel.
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• MERCURY
Mercury is closest to the sun.
It has no moons.
It is a little larger than our moon.
The surface has many flat plain-like areas and
craters.
It has a very thin atmosphere of sodium and other
gases.
Since it has little atmosphere and is so close to the
sun its temperatures range from 450º C to -170º C.
The
evening
sky
Mercury up close
Mercury, really close
VENUS
• Venus is about the size and in many ways the
same structure as Earth.
• There are, however, many ways in which it
differs.
• It takes Venus 7.5 Earth-months to revolve
around the sun.
• It takes Venus 8 Earth-months to rotate on its
axis. On Venus a day is longer than a year.
• Venus also rotates in a direction that is opposite
of all the other planets. That is called retrograde
rotation.
• Venus’ atmosphere is very thick. Every day is
cloudy.
• The atmosphere is 90 times greater than ours. If
you were on the surface you would be crushed.
• The atmosphere is almost all carbon dioxide with
some sulfuric acid as well. A human could not
survive.
• The carbon dioxide traps the sun’s energy so the
temperature gets up to 460ºC and stays there.
• That is called the greenhouse effect.
• Venus is mostly rock with volcanoes and lava
flow.
Venus: shrouded with clouds
composed of sulfuric acid
Radar can
see
through
the clouds
to the
surface of
Venus
Venus rotates “backward” compared to the other
inner planets. Note other differences between the
planets’ motions.
MARS
• Mars is called the red planet because it has an
iron oxide surface that is red.
• It has a very thin atmosphere that is mostly
carbon dioxide.
• There is some solid water at the north pole of
Mars. This is covered with solid carbon dioxide
in the winter.
• Mars is tilted on its axis so it has seasons. During
the change of seasons many dust storms exist.
• Mars has two very small moons called Phobos
and Deimos.