1. Chapter 7 Our 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?

4. Eight major planets with nearly circular orbits
Planets all orbit in same direction and nearly in same plane
Pluto is smaller than the major planets and has a more elliptical orbit

5. Thought Question How does the Earth-Sun distance compare with the Sun’s radius
It’s about 10 times larger.
It’s about 50 times larger.
It’s about 200 times larger.
It’s about 1000 times larger.

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

7. Comparative Planetology
We can learn more about a world like our Earth by studying it 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.

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

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

10. As you already know: 1. the planets are very tiny compared to distances between them. 2. The four innermost planets are much closer together compared to the outer four planets.
Before embarking on the tour of the planets, you might wish to review the overall scale from ch. 1.

11. Sun Over 99.9% of solar system’s mass Made mostly of H/He gas (plasma)
These slides follow the planetary tour pages in ch. 7.
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

12. Mercury Made of metal and rock; large iron core
Why so many craters? Why so sharp in appearance?
Mercury
Made of metal and rock; large iron core
Desolate, cratered; long, tall, steep cliffs
Very hot and very cold: 425°C (day), –170°C (night)

13. Venus Nearly identical in size to Earth; surface hidden by clouds
Hellish conditions due to an extreme greenhouse effect:
Even hotter than Mercury: 470°C, day and night

14. Earth
Earth and Moon to scale
An oasis of life
The only surface liquid water in the solar system
A surprisingly large moon

15. Mars Looks almost Earth-like, but don’t go without a spacesuit!
Giant volcanoes, a huge canyon, polar caps, more…
Water flowed in distant past; could there have been life?

16. Jupiter Much farther from Sun than inner planets
Mostly H/He; no solid surface
300 times more massive than Earth
Massive enough to fit the rest of the solar system inside it.
Many moons (63), rings …

17. Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons
Io (shown here): Active volcanoes all over
Europa: Possible subsurface ocean
Ganymede: Largest moon in solar system (bigger than Hg)
Callisto: A large, cratered “ice ball”

18. Saturn Giant and gaseous like Jupiter Spectacular rings
Many moons, including cloudy Titan

19. Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.
Artist’s conception

20. Uranus Smaller than Jupiter/Saturn; much larger than Earth
Made of H/He gas & hydrogen compounds (H2O, NH3, CH4)
Extreme axis tilt
Moons & rings

21. Neptune Similar to Uranus (except for axis tilt)
Many moons (including Triton)
Note: this is the same image as in the text but rotated 90° to show the axis tilt relative to the ecliptic plane as the horizontal on the page. (The orientation in the book chosen for its more dramatic effect.)

22. Pluto (and other Dwarf Planets)
Much smaller than major planets
Icy, comet-like composition
Pluto’s main moon (Charon) is of similar size

23. This important summary table may be worth some time in class to make sure students understand how to read it…

24. Thought Question What process created the elements from which the terrestrial planets were made?
The Big Bang
Nuclear fusion in stars
Chemical processes in interstellar clouds
Their origin is unknown

25. 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

26. What have we learned?
What are the major features of the Sun and planets?
Sun: Over 99.9% of the mass
Mercury: A hot rock
Venus: Same size as Earth but much hotter
Earth: Only planet with liquid water on surface
Mars: Could have had liquid water in past
Jupiter: A gaseous giant
Saturn: Gaseous with spectacular rings
Uranus: A gas giant with a highly tilted axis
Neptune: Similar to Uranus but with normal axis
Dwarf Planets: Most (like Pluto) are icy like comets

27. 7.2 Patterns in the Solar System
Our goals for learning:
What features of our solar system provide clues to how it formed?

28. What features of our solar system provide clues to how it formed?

29. Motion of Large Bodies
All large bodies in the solar system orbit in the same direction and in nearly the same plane
Most also rotate on their axes in the same direction

30. Two Main Planet Types
Terrestrial planets are rocky, relatively small, and close to the Sun
Jovian planets are gaseous (H, He, H2O, NH3, CH4), larger, and farther from Sun

31. Two Main Planet Types
Terrestrial planets have higher density and solid surface.
Jovian planets are much colder in comparison.

32. Comparison of Terrestrial and Jovian Planets

33. Swarms of Smaller Bodies
Many rocky asteroids and icy comets populate the solar system.
Objects are located in the:
Asteroid belt
Kuiper belt
Oort cloud

34. Asteroids
Asteroids are small, rocky bodies that orbit the Sun much like planets, but they are much smaller than planets.
The asteroid belt exists between Mars and Jupiter where most of these objects exist.
Some asteroids also exist in the Kuiper belt.
Eros

35. Comets
Small objects made largely of ices (such as water ice, ammonia ice, and methane ice) mixed with rock .
Comets have very elliptical orbits.
Spend most of their time in the Kuiper belt or Oort cloud beyond Neptune.
Hale – Bopp Comet S

36. Notable Exceptions
Several exceptions to the normal patterns need to be explained
Uranus’ tilted axis.
Earth’s large moon.
Venus’ retrograde rotation.

37. How did we learn the scale of the solar system?
From Kepler’s Laws, we knew distances in astronomical units (AU), distances relative to the Earth – Sun distance.
We did not have a measurement in meters or kilometers
In 1716, Edmund Halley suggested that we use parallax when Venus is in transit (when a planet passes in front of the Sun)
Unfortunately, The transit of Venus occurs very infrequently
About 2X every 120 years and only 8 years apart!

38. Transit of Venus
Apparent position of Venus on Sun during transit depends on distances in solar system and your position on Earth.
Transit only occurs for the inferior planets (Venus and Mercury)
For Venus, the episode lasts for more than 6 hours.
Transit of Venus: June 8, 2004

39. Determining the scale of the solar system.

40. Measuring Distance by Parallaxθ
Lateral distance
Using basic trigonometry: If you know one side of a right triangle and one of the angles, you can figure out any of the other sides of the triangle.
Since we know the radius of the Earth, and we can measure the angle that Venus makes with observers at any two locations on the surface of the Earth, we can determine the true value for an AU.

41. Measuring Distance by Parallax
Locations of two observers. θ

42. 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.

43. 7.3 Spacecraft Exploration of the Solar System
Our goals for learning:
How do robotic spacecraft work?

44. How do robotic spacecraft work?

45. Flybys A flyby mission flies by a planet just once
Cheaper than other mission but have less time to gather data
Voyagers 1 & 2, Dawn, New Horizons.

46. Orbiters Go into orbit around another world
More time to gather data but cannot obtain detailed information about world’s surface
Magellan, Galileo, Mars Global Surveyor, NEAR, Mars Odyssey 2001, Venus Express, Mars Express, Cassini, Mars Reconnaissance Orbiter, Messenger.

47. Probes or Landers Land on surface of another world
Explore surface in detail
Vikings 1 & 2, Mars Pathfinder, Mars Exploration Rovers (Spirit & Opportunity), Deep Impact, Hayabusa, Rosetta.

48. Combination Spacecraft
Cassini/Huygens mission contains both an orbiter (Cassini) and a lander (Huygens)

49. Sample Return Missions
Land on surface of another world
Gather samples
Spacecraft designed to blast off other world and return to Earth
Apollo missions to Moon are only sample return missions to date
Stardust – Visited Comet Wild 2.
Hayabusa – Collected asteroid sample.

50. What have we learned? How do robotic spacecraft work?
Flyby: Flies by another world only once.
Orbiter: Goes into orbit around another world
Probe/Lander: Lands on surface
Sample Return Mission: Returns a sample of another world’s surface to Earth