Transcript THE INNER PLANETS

THE INNER PLANETS
• The four inner planets are small and
dense and have rocky surfaces. The inner
planets are often called “terrestrial
planets,” from the Latin word “terra” which
means “Earth.”
Mercury
• Mercury is the smallest
terrestrial planet and
the planet closest to
the sun. It is not much
larger than Earth’s
moon and has no
moons of its own. The
inside of Mercury is
most likely made up of
the dense metal iron.
• Mercury has many flat plains and craters on its
surface. Mercury also has virtually no
atmosphere due to its high daytime
temperatures. The side of Mercury that faces
the sun can reach temperatures of 430 degrees
Celsius. However, because Mercury has no
atmosphere, at night its heat escapes into
space causing temperatures to drop to -170
degrees Celsius.
Venus
• Venus is similar in
mass and size to Earth
that it is known as
“Earth’s twin.”
Although Venus and
Earth have similar
internal structures and
densities, they are very
different in other ways.
• Venus’s atmosphere is so thick that it is always
cloudy there. These clouds are mostly made of
sulfuric acid. The pressure of Venus’s
atmosphere is 90 times greater than Earth’s,
which means you would be crushed by it if you
were to stand on Venus’s surface. You could not
breathe on Venus because its atmosphere is
mostly carbon dioxide (which is what WE
breathe out!).
• At 460 degrees
Celsius, Venus has
a surface
temperature hot
enough to melt lead.
Its surface has
many volcanoes and
broad plains formed
by lava flows.
Earth
• Earth has 3 main layers:
the crust, mantle, and
core. The crust includes
the solid, rocky surface.
Under the crust is the
mantle, a layer of hot
molten rock. Earth has a
dense core made of
mainly iron and nickel.
The outer core is liquid,
but the inner core is solid.
• Earth is unique in our solar system in
having liquid water at its surface. About
70 percent of Earth’s surface is water.
• Earth has enough gravity to hold on to most gases.
These gases make up Earth’s atmosphere, which
extends more than 100 kilometers above its surface.
Although some other plates also have atmospheres,
Earth is the only one that is rich in oxygen. The rest of
its atmosphere is mostly nitrogen.
Mars
• Mars is called the “red
planet” because it has
a reddish color in the
sky. The red color is
caused by the
breakdown of iron-rich
rocks, which causes a
rusty dust that covers
Mars’s surface.
• Mars’s atmosphere is more than 95 percent
carbon dioxide (similar to Venus’s
atmosphere, but much thinner), and contains
few clouds. Because Mars has a
transparent atmosphere, its surface is easily
viewed from Earth through a telescope.
Mars has temperatures that range from -140
degrees Celsius to 20 degrees Celsius.
• Scientists think that a large amount of
liquid water flowed on Mars’s surface in
the distant past. For this to be true,
Mars must have been much warmer and
had a thicker atmosphere at that time.
Today, liquid water cannot exist on Mars
for very long. Since Mars’s atmosphere
is so thin, liquid water would quickly turn
into gas. Much of the water on Mars
exists in its polar ice caps.
• The surface of Mars is
barren and covered
with craters like the
moon. Some regions
of Mars have giant
volcanoes.
Astronomers see signs
that lava flowed from
the volcanoes in the
past, but the volcanoes
are no longer active.