Download Chapter 9 Lesson 2

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Rings Around a Planet:
Saturn’s rings have fascinated sky gazers
since the astronomer Galileo first saw
them in 1610. We’ve learned that the
rings are made of rock, gas, and ice.
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 A solar system is a group of objects in space that orbit a star in the
center, plus the star itself. The sun is the star in the center of our solar
system.
 Our solar system contains a variety of objects. These include planets
and moons as well as asteroids, which are small and rocky.
 A planet is a large object that orbits a star. A moon is a smaller object
that orbits a planet.
 In our solar system, there are EIGHT (8) planets. Pluto is now
considered a dwarf planet, so there are no longer 9 planets .
 Often scientists group them as the inner planets (closer to the sun)
and the outer planets (farther from the sun). The groups are
separated by a ring of asteroids.
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o The inner planets are those closest to the sun; they are Mercury,
Venus, Earth, and Mars. These planets are alike in many ways. They all
have rocky surfaces and are smaller than most of the outer planets.
Also, none of the inner planets has more than two moons.
o There are also many differences—Mercury is hot enough to melt lead
while Mars never gets above 68°F.
o Earth is the most unusual inner planet. Only Earth has liquid water on its
surface and a large amount of oxygen in the atmosphere. This water
and oxygen help support life on Earth.
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o Beyond Mars, on the far side of the asteroid belt, are the outer
planets. They are Jupiter, Saturn, Uranus, and Neptune.
o These 4 planets are huge and made mostly of gases. They are often
called the gas giants.
o They all have many moons, and they all are surrounded by rings that
are made of dust, ice, or rock.
o Pluto is no longer considered an outer planet .