Download The Outer Planets

The Outer Planets
The outer planets—Jupiter, Saturn, Uranus, and Neptune—are much larger and more massive
than Earth, and they do not have solid surfaces. Because these four planets are all so large, they are
often called the gas giants.
Like the sun, the gas giants are composed mainly of hydrogen and helium. Because they are so
massive, they exert a much stronger gravitational force than the terrestrial planets. This prevents their
gases from escaping, so they have thick atmospheres. All of the giants have many moons and are
surrounded by a set of rings. A ring is a thin disk of small particles of ice and rock.
Jupiter is the largest and most massive planet. Jupiter has a thick atmosphere made up mainly of
hydrogen and helium. An interesting feature of Jupiter’s atmosphere is its Great Red Spot, a storm
that is larger than Earth. Jupiter probably has a dense core of rock and iron at its center, surrounded
by a thick mantle of liquid hydrogen and helium. Galileo discovered Jupiter’s four largest moons: Io,
Europa, Ganymede, and Callisto.
Saturn is the second-largest planet in the solar system. Its average density is less than that of
water. The rings around Saturn are made of chunks of ice and rock. Saturn has the most spectacular
rings of any planet.
Uranus is about four times the diameter of Earth and is twice as far from the sun as Saturn.
Uranus looks blue-green because of traces of methane in its atmosphere. Uranus’s axis of rotation is
tilted at an angle of about 90 degrees from the vertical. It rotates from top to bottom instead of from
side to side.
Neptune is a cold, blue planet. Its atmosphere contains visible clouds. Neptune was discovered
as a result of a mathematical prediction. Astronomers have discovered at least 13 moons orbiting
Neptune.
Answer the following question in the spaces provided.
1. What are the four outer planets? __________________________________________________________________
2. Why doesn’t the gas on a gas giant escape into space, as it has on Mercury?
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3. What object in the solar system has a composition similar to that of the gas giants?
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4. What planet is by far the most massive of all the planets that revolve around the sun?
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5. What are Saturn’s rings made of? _________________________________________________________________
6. How did astronomers know where to look to discover Neptune?______________________________________
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7. Define gas giant. _________________________________________________________________________________
8. What is a ring? __________________________________________________________________________________
Inner Planets
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 –140°C to
20°C. 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.
Write the inner planet or planets that the statement describes.
1._______________________
1. has a rocky surface
2._______________________
2. 70 percent is covered with water
3._______________________
5._______________________
3. rotates in the opposite direction from most other planets and
moons
4. called the “red planet” because of the color of the dust
5. has at least one moon!
6._______________________
6. similar to each other in size, density, and internal structure
7._______________________
7. has almost no atmosphere
8._______________________
8. atmosphere is so heavy and thick that it would crush a human
9._______________________
9. has a tilted axis that causes seasons
4._______________________
10.______________________
!10. atmosphere has low air pressure and is mostly carbon dioxide