Download The Planets

The Solar System
Section 2
The Inner Planets
〉 How are the inner planets similar to one another?
〉 The terrestrial planets are relatively small and have
solid, rocky surfaces.
• terrestrial planet: one of the highly dense planets
nearest to the sun: Mercury, Venus, Earth, and Mars.
The Solar System
The Inner Planets
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The Solar System
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The Inner Planets, continued
• Mercury has extreme temperatures.
– Mercury is the closest planet to the sun.
– One year there is only 88 days on Earth.
– The side of Mercury facing the sun can reach 720 K. The
side facing away from the sun is only 103 K.
– Mercury is covered by craters.
The Solar System
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• Thick clouds on Venus cause a greenhouse effect.
– Venus has a thick atmosphere containing large amounts of
sulfuric acid.
– The atmospheric pressure on Venus is 90 times that of
Earth.
– A runaway greenhouse effect keeps the surface temperature
above 700 K.
The Solar System
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• Earth has ideal conditions for living creatures.
– Earth is the only planet known to harbor life.
• hydrosphere: the portion of Earth that is water
• The atmosphere protects Earth from radiation.
– Earth’s atmosphere is 78% nitrogen, 21% oxygen, and 1%
carbon dioxide and other gases.
– The atmosphere protects Earth from harmful radiation and
high-energy particles emitted by the sun.
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• Many missions have explored the planet Mars. Mars
has many extreme landforms.
– The Martian volcano Olympus Mons is the largest
mountain in the solar system.
– The surface of Mars is red from large amounts of
iron oxide in the soil.
The Solar System
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• An asteroid belt lies beyond the orbit of Mars.
– The dwarf planet Ceres is in the asteroid belt.
• asteroid: a small, rocky object that orbits the sun;
most asteroids are located in a band between the
orbits of Mars and Jupiter
• dwarf planet: a celestial body that orbits the sun, is
round because of its own gravity, but has not cleared
its orbital path
The Solar System
Section 2
The Gas Giants
〉 What are gas giants?
〉 The outer planets are much larger than the inner
planets and have thick, gaseous atmospheres, many
satellites, and rings.
• A gas giant is a planet that has a deep, massive
atmosphere: Jupiter, Saturn, Uranus, and Neptune.
All the gas giants have rings and satellites.
The Solar System
The Gas Giants
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The Solar System
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The Gas Giants, continued
Jupiter is the largest planet in the solar system.
– Jupiter is big enough to hold 1300 Earths.
– Jupiter rotates once around its axis in less than 10
hours.
– Jupiter’s atmosphere has swirling clouds of
hydrogen, helium, methane, and ammonia.
– Jupiter has more than 60 satellites.
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• Saturn has the most extensive ring system.
– Saturn is 95 times the mass of the Earth and takes
over 29 y to orbit the sun. It rotates in 10.7 h.
– Saturn’s rings are narrow bands of tiny particles of
dust, rock, and ice.
– Saturn has more than 40 satellites.
– Saturn may still be forming.
– Saturn radiates three times more energy than it
receives from the sun.
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The Gas Giants, continued
• Uranus and Neptune are blue gas giants.
– They hold thick, gaseous atmospheres composed of
hydrogen, helium, and methane.
– The methane gives both planets a bluish color.
– Uranus is 14 Earth masses, and it takes about 84 y
to orbit the sun at its distance of 19 AU.
– Neptune is 17 Earth masses, and takes
approximately 164 y to orbit the sun at a distance
of 30 AU.
The Solar System
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Beyond the Gas Giants
〉 What type of bodies lie beyond the gas giants?
〉 Beyond the gas giants are numerous small bodies
composed of ice and rock.
• Not all large objects in the solar system are planets.
– The scientific definition of planet was decided upon
in 2006 by the International Astronomical Union.
– Pluto, formerly considered a planet, was reclassified
as a dwarf planet.
The Solar System
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Beyond the Gas Giants, continued
• There are many objects beyond Neptune.
– Beyond Neptune lies the Kuiper Belt.
– The Kuiper Belt contains many small bodies of ice
and rock.
– Scientists think that these bodies are the remnants
of the material that formed the solar system.
– At least two dwarf planets, Pluto and Eris, can be
found in the Kuiper Belt.