The Inner
Planets
Mercury, Venus, Earth
and Mars
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Vocabulary
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Vocabulary
Rotation
Revolution
Orbit
Diameter
Satellite
Atmospheric
Geological
Gathering information about the
INNER PLANETS!
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The Inner Planets!
Mercury

The planet closest to the sun is Mercury.
Mercury is not much larger than Earth’s moon
and has no moons of its own. Mercury is made
up mainly of the dense metals iron and nickel.

Mercury has many flat plains and craters on its
surface. The craters on Mercury have been
named for artists, writers, and musicians
including the composers Bach and Mozart.
Mercury Continued
Mercury Continued

Mercury has an extremely thin atmosphere. Astronomers have
detected small amounts of sodium and helium. Mercury is a planet
of extremes. It is so close to the sun that during the day, the side
facing the sun reaches temperatures of 450˚C. Because Mercury
has almost no atmosphere, at night all the heat escapes into space.
The temperature drops to -170˚C. Mercury thus has a greater range
of temperatures than any other planet in the solar system.
Average
distance from
Sun
Diameter (km)
Period of
Revolution
(Earth days)
Rate of
Rotation (Earth
days)
58,000,000
4,878
88
59
Take away fact:
Mercury resembles the moon!
Venus

Venus is so similar in size to Earth that it is sometimes called Earth’s twin.
Astronomers think that the density and internal structure of Venus are
similar to Earths; however, Venus differs in many other ways.

Venus is the second planet from the sun; therefore, it receives a great deal
of light. Ordinary light from the sun causes Venus’s surface to heat up. In
turn, carbon dioxide traps this heat in the atmosphere causing Venus’s
surface to become hotter and hotter, until it is about 460˚C—hot enough to
melt lead. This trapping of heat by the atmosphere is called the
greenhouse effect.

Venus takes about 7.5 Earth months (225 days) to revolve around the sun.
It takes about 8 months (243 days) for Venus to rotate on its axis. Venus
rotates so slowly that its “day” is longer than its “year.” Oddly, Venus rotates
from east to west, the opposite direction from most other planets and
moons. This type of rotation is called retrograde rotation, from the Latin
words for “moving backward.” One hypothesis proposed by astronomers to
explain this unusual rotation is that Venus was struck by a very large object
billions of years ago. This collision caused the direction of its rotation to
change.
Venus Continued
Venus Continued

Venus is covered with rock, similar to many rocky areas on Earth.
Venus has volcanoes with lava flow, many craters and strange
domes not found on other planets.

Venus is also known as the "morning star" or the "evening star"
since it is visible and quite bright at either dawn or dusk. It is only
visible at dawn or dusk since it is closer to the sun than we are.
Average
distance from
Sun
Diameter
(km)
Number of
Satellites
(moons)
Dominant
Atmospheric Gases
108,000,000
12,104
0
Mostly CO2 gas
(Greenhouse effect)
Partly Sulfuric Acid
Take away fact:
Venus has retrograde rotation!
Earth

The Earth is the third planet from the Sun in our Solar System. It is the
planet we evolved on and the only planet in our Solar System that is known
to support life. Earth is 12,756 km in diameter, the fifth largest!

Our planet’s atmosphere extends more than 100 kilometers above Earth’s
surface. The oxygen you need to live makes up about 20 percent of the
gases in Earth’s atmosphere. Almost all the rest is nitrogen gas, with a
small amount of carbon dioxide. Earth’s atmosphere also contains water
vapor and clouds of water droplets.

Most of Earth, about 70 percent, is covered with water. Perhaps the planet
should be named “Water” instead of “Earth”! No other planet in our solar
system has oceans like Earth’s.

Earth has three main layers—a crust, a mantle, and a core. The crust
includes the solid rocky surface. Under the crust is the mantle, a layer of
hot molten rock. When volcanoes erupt, this hot material rises to the
surface. Earth has a dense inner core made up mainly of iron and nickel
Earth Continued
Earth Continued

Our Earth has one satellite or moon which is about ¼ of
the diameter of Earth. Some scientists hypothesize that
the moon may have once been a part of the Earth: it may
have been broken off during a catastrophic collision of a
huge body with the Earth billions of years ago.
Average
distance from
Sun
Period of
Revolution
(Earth days)
Rate of Rotation
(Earth days)
Surface
Temperature
(˚C)
150,000,000
365 days
1 day
(23 hrs, 56 min.)
-88˚C
58˚C
Take away fact:
Earth is 70% water!
Mars

Mars is the farthest inner planet from the sun, approximately
228,000,000 kilometers away. Mars is called the “red planet”
because it has a slightly reddish color when you see it in the sky.
The atmosphere of Mars is mostly carbon dioxide. In the early
1900’s, two Italian astronomers convinced many people that there
were canals on Mars that had been built by intelligent Martians to
carry water. Astronomers now know that this was a mistake. There
are no canals on Mars; however, we have found that some water
remains in the form of ice at its north pole. Unlike Earth’s ice caps,
during the winter this polar cap is covered by a layer of frozen
carbon dioxide.

For the most part, Mars is deserted and covered with craters like the
moon. Some regions of Mars have giant volcanoes that show signs
of lava flow. The rocks on Mars look red because they are covered
with a rusty dust. There are also deep canyons possibly formed by
fault zones.
Mars Continued
Mars Continued

Mars has two very small moons. Phobos, the larger moon, is only
27 kilometers in diameter, about the distance a car can travel on the
highway in 15 minutes. Deimos, is even smaller, only 15 kilometers
in diameter. Close-up views from space show that, like Earth’s
moon, Phobos and Deimos are covered with craters.
Diameter (km)
Period of
Revolution
(Earth days)
Rate of
rotation (Earth
days)
Surface
Temperature
(˚C)
6,794
687 days
1 day
(24 hrs. 37
min.)
-87˚C
-5˚C
Take away fact:
Mars has the largest volcanoes
in our Solar System!
Revolution
The movement of an object
around another object!
Geological
The physical characteristics,
especially the surface features of
an area (mountains, craters, etc)!
Satellite
Any object that revolves
around another object in
space (moon)!
Diameter
A straight line connecting
two points of a circle
(size).
Orbit
The path of an object as it
revolves around another
object in space!
Rotation
The spinning motion of
a planet about its axis!
Atmospheric
The air or climate in a
specific place!
QUIZ TIME!!!!!
Time to test out what you have
learned!
Click here to
start the quiz!
1. Which planet is green and blue,
and has an average diameter of
12,756 kilometers?
a. Mercury
b. Venus
c. Earth
d. Mars
2. Which planet orbits the sun once
every 687 days, and has the largest
volcanoes in our solar system?
a. Mercury
b. Venus
c. Earth
d. Mars
3. Which planet is about the same
size as Earth, shows evidence of
volcanic activity, but is so hot you
wouldn’t be able to live?
a. Mercury
b. Venus
c. Earth
d. Mars
Correct!!!
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Make sure you record your
answer in Chart 1.
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Look at your chart 1:
Terrestrial Planets!
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You have learned
all about the
inner planets!
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