1. Section 2: The Inner and Outer Planets
Preview
Key Terms
Bellringer
The Inner Planets
The Gas Giants
Beyond the Gas Giants

2. Key Terms How are the inner planets similar to one another?
What are gas giants?
What type of bodies lie beyond the gas giants?

3. Bellringer
Based on what you have learned, as well as previous knowledge, answer the following questions.
Our solar system consists of the sun and eight planets. Make a list of at least six of the planets in our solar system.
Do you think that all of the planets in our solar system have the same composition? If not, describe some of the possible differences.
Scientists have sent many probes to explore and study Mars. What similarities does Mars share with Earth? What are some differences?

4. 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
The terrestrial planets are: Mercury, Venus, Earth, and Mars.

5. The Inner Planets

6. Visual Concept: Astronomical Unit (AU)

7. Visual Concept: Day, Rotation, Period of Rotation

8. Visual Concept: Year, Revolution, Period of Revolution

9. 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.

10. The Inner Planets, continued
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.

11. The Inner Planets, continued
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.

12. The Inner Planets, continued
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.

13. The Inner Planets, continued
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

14. 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.
gas giant: a planet that has a deep, massive atmosphere
The gas giants are: Jupiter, Saturn, Uranus, and Neptune.

15. The Gas Giants

16. The Gas Giants, continued
All the gas giants have rings and satellites.
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.

17. The Gas Giants, continued
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.

18. 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.

19. Visual Concept: Inner and Outer Planets

20. Visual Concept: Comparing Prograde and Retrograde Motions

21. 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.

22. 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.