Download Solar System Study Guide 1

Solar System Study Guide 5
The Inner Planets:
 The area of the asteroid belt can be thought of as a dividing line between two
groups of planets, the inner and the outer. The inner planets – Mercury, Venus,
Earth, and Mars – lie between the sun and the asteroid belt.
 Like the asteroids, the inner planets are rocky and dense.
 Unlike the asteroids, these planets are large and, except for Mercury, have
atmospheres.
 Mercury, the planet closest to the sun, is about the size of Earth’s moon.
 Mercury, which is covered with craters, even looks like the moon.
 Very small amounts of gases are present on Mercury, but there aren’t enough of
them to form an atmosphere.
 Venus, the second planet from the sun, is about the same size as Earth. But Venus
is very different from Earth. Venus is very dry and has a thick atmosphere that
transfers heat. The thick atmosphere presses down on Venus with a weight 100
times that of Earth’s atmosphere. Also, Venus spins on its axis in a direction
opposite from that of Earth’s rotation.
 Earth, the third planet from the sun is the largest of the inner planets. It has one
natural satellite, the moon. Earth is the only planet that has liquid water. It is also
the only known planet that supports life.
 Earth’s atmosphere absorbs and reflects the right amount of solar energy to keep
the planet at the correct temperature for living things such as humans to survive.
 Mars, the fourth planet from the sun, is sometimes called the Red Planet because
its soil is dark reddish brown.
 Mars has two moons and the largest volcano in the solar system – Olympus
Mons.
 Space probes have shown us that nothing lives on Mars. Dust storms can last for
months and affect the whole planet.
 It is believed that liquid water once existed on Mars. This is because probes and
satellites have found deep valleys and sedimentary rocks. These features
probably were formed by flowing rocks. NEWS UPDATE: In August 2008 ice
water was found on Mars!
The Outer Planets:
 On the other side of the asteroid belt are the outer planets – Jupiter, Saturn,
Uranus, and Neptune.
 Four of these planets – Jupiter, Saturn, Uranus, and Neptune – are large spheres
made up mostly of gases. Because of this, these planets are often called the gas
giants.
 Jupiter is the largest planet in our solar system. The three thin rings that
surround it are hard to see.
 At least 16 moons orbit Jupiter.
 Jupiter’s atmosphere is very active. Its energy causes a circular storm known as
the Great Red Spot. This weather, which is a lot like a hurricane, has lasted more
than 300 years. It is so big around that three Earth’s would fit inside it.
 Saturn is a gas giant known for its rings.
 Saturn has at least 18 moons.
 Uranus, the seventh planet from the sun, is a blue-green ball of gas and liquid.
 Neptune, the eighth planet from the sun, is blue green because its clouds contain
methane ice crystals.
 Dwarf Planet Pluto: From Pluto’s surface, the sun looks like a very bright star.
 Little heat or light reaches Pluto or its moon.
 Pluto has a rocky surface that is probably covered by frozen gases.
Moons and Rings:
 Every planet except Mercury and Venus has at least one natural satellite (moon).
 Earth’s moon is round and rocky, and it has many craters.
 Others, like the two moons of Mars or the outer moons of Jupiter, are small and
rocky and have uneven shapes.
 Jupiter and Mars orbit near the asteroid belt, so their moons may be asteroids
pulled in by the planets’ gravity.
 The large moons of Jupiter and Saturn are almost like small planets.
 Io, one of Jupiter’s larger moons, has active volcanoes.
 Titan, one of Saturn’s moons, has a dense atmosphere that glows red-orange.
 Besides having moons, each of the gas giants has a system of rings. These rings
are made of tiny bits of dust, ice crystals, and small pieces of rock.
 Saturn’s rings may have formed as a moon was pulled apart by gravity because it
got too close to the planet.
Harcourt Science D74-81