Download The Inner Planets

Name ____________________________ Date ____________________ Class ____________
The Solar System
■
Section Summary
The Inner Planets
Guide for Reading
■ What characteristics do the inner planets have in common?
■
What are the main characteristics that distinguish each of the
inner planets?
© Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.
The Solar System
Mercury, Venus, Earth, and Mars are more similar to one other than they are
to the five outer planets. The four inner planets are small and dense and
have rocky surfaces. These planets are often called the terrestrial planets,
from the Latin word terra, or “earth.”
Earth is unique in our solar system in having liquid water at its
surface. Earth has a suitable atmosphere and temperature range for water to
exist as liquid, gas, or solid. Earth has an atmosphere that is rich in oxygen.
Nearly all of the remaining atmosphere consists of nitrogen, along with
small amounts of other gases such as argon and carbon dioxide. The
atmosphere also includes water vapor.
Mercury is the smallest terrestrial planet and the planet closest to the
sun. Mercury is smaller than Earth’s moon and has no moons of its own. The
planet’s interior is probably made of iron, and its surface has many plains
and craters. Because the planet is so close to the sun, the side facing the sun
reaches temperatures of 430°C. However, the temperature drops to –170°C
at night.
Venus is similar in size and mass to Earth. Venus’ density and internal
structure are similar to Earth’s. But in other ways, Venus and Earth are very
different. Venus rotates from east to west, the opposite direction from most
other planets and moons. The pressure of Venus’s atmosphere is 90 times
greater than the pressure of Earth’s atmosphere. The atmosphere is mostly
carbon dioxide, with clouds partly made up of sulfuric acid. The carbon
dioxide in the planet’s atmosphere traps the sun’s heat, causing the surface
temperature of Venus to be about 460°C. This trapping of heat by the
atmosphere is called the greenhouse effect. Venus is covered with rock,
similar to many rocky areas on Earth. Venus also has many volcanoes and
broad plains formed by lava flows.
Mars is called the “red planet.” Its surface is covered with red dust. The
planet Mars has a very thin atmosphere that is mostly carbon dioxide.
Temperatures on the surface range from –140ºC to 20ºC. Images of Mars
show a variety of features that look as if they were made by ancient streams,
lakes, or floods. Scientists think that a large amount of liquid water flowed
on Mars’s surface in the distant past. At present, liquid water cannot exist
for long on Mars’s surface. However, some water is frozen in the planet’s
two polar ice caps. A large amount of water may be frozen underground.
Like Earth, Mars is tilted on its axis, so its seasons change. Some regions of
Mars have giant volcanoes. Mars has two very small moons, Phobos and
Deimos.