Chapter 7 Our Planetary System

1. Chapter 7Our Planetary System Earth, as viewed by the Voyager spacecraft

2. 7.1 Studying the Solar System • Our goals for learning • What does the solar system look like? • What can we learn by comparing the planets to one another? • What are the major features of the Sun and planets?

3. What does the solar system look like? 1. What is in it?

4. Eight major planets with nearly circular orbits • Pluto (dwarf planet) is smaller than the major planets and has a more elliptical orbit

5. What Counts as a Planet? The IAU definition of a planet (2006): • is in orbit around the Sun, • has sufficient mass so that it is nearly round • has "cleared the neighborhood" around its orbit.

6. History of Planet Count • The number of objects counted as planets in the solar system has varied over the centuries • As low as 6 and has high as 13

7. What does the solar system look like? 2. How far apart . are things? Planets are very tiny compared to distances between them.

8. What can we learn by comparing the planets to one another?

9. Comparative Planetology • We can learn more about a world like our Earth by studying in context with other worlds in the solar system. • Stay focused on processes common to multiple worlds instead of individual facts specific to a particular world.

10. Comparing the planets reveals patterns among them • Those patterns provide insights that help us understand our own planet

11. What are the major features of the Sun and planets? Sun and planets to scale

13. Density and Composition Density = mass _ volume g/cm3 • Measure a planet’s volume • Measure a planet’s spin => calculate mass • Result is a world’s bulk density.

14. Density and Composition • Common materials • Iron 7.9 g/cm3 • Basalt 3.3 g/cm3 (rock) • Carbon and hydrogen ices 0.4-1.5 g/cm3 (volatiles) • H and He <<0.01 g/cm3

15. Density and Composition • Earth 5.5 g/cm3 composition- iron, rock • Saturn 0.7 g/cm3 composition- some rock, volatiles and lots H&He • Callisto 1.9 g/cm3 Titan 2 g/cm3 composition -rock and ice

16. Thought Question Planet Mars has a bulk density of 3.9 g/cm3 What materials is it made of ? • Iron 7.9 g/cm3 • Basalt 3.3 g/cm3 • Volatiles 1-1.5 g/cm3 • H and He <<0.01 g/cm3

17. Thought Question Planet Mars has a bulk density of 3.9 g/cm3 What materials is it made of ? • Iron 7.9 g/cm3 • Basalt 3.3 g/cm3 • Volatiles 1-1.5 g/cm3 • H and He <<0.01 g/cm3

18. What have we learned? • What does the solar system look like? • Planets orbit Sun in the same direction and in nearly the same plane. • What can we learn by comparing the planets to one another? • Comparative planetology looks for patterns among the planets. • Those patterns give us insight into the general processes that govern planets • Studying other worlds in this way tells us about our own Earth

19. What have we learned? • How can we tell what planets are made of? • The bulk density of the planets reflect the type of materials the planets are composed of. • There are 4 main common types of material • Most planets are made of a mixture of these materials that are not necessarily represented on the surface.

20. What features of the solar system provide clues to how it formed?

21. All large bodies in the solar system orbit in the same direction and in nearly the same plane

22. Motion of Large Bodies • Most also rotate in the direction of orbit.

23. Sun • Over 99.9% of solar system’s mass • Made mostly of H/He gas (plasma) • Converts 4 million tons of mass into energy each second

24. Two Main Planet Types • Terrestrial planets (rocky worlds) • Jovian planets • (gas giant worlds)

25. The rocky worlds are the 4 inner planets plus our Moon They have a solid rock surface with an iron core and a weak or no atmosphere.

26. There are 4 gas giant planets in our solar system. These planets have NO solid surfaces – just gas and clouds that get denser as you move to their center.

27. gas giant worlds are far from the Sun Rocky worlds are close to the Sun.

28. Jupiter – largest gas giant world gas giant worlds are much larger than rocky worlds Earth – largest rocky world

29. Rocky worlds have no rings and no, or few, moons. Gas Giant worlds have rings and many moons.

30. Swarms of Smaller Bodies • Many rocky asteroids and icy comets populate the solar system

31. Notable Exceptions • Several exceptions to the normal patterns need to be explained

32. What have we learned? • What features of the solar system provide clues to how it formed? • Motions of large bodies: All in same direction and plane • Two main planet types: Terrestrial and jovian • Swarms of small bodies: Asteroids and comets • Notable exceptions: Rotation of Uranus, Earth’s large moon, etc.