1. Summary of Our Solar System
Earth, as viewed by the Voyager spacecraft

2. Studying the Solar System
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?
How do we learn these things?

3. What does the solar system look like?
Planets are tremendously
exaggerated in size compared to their separations
The inner, terrestrial planets are very different from the outer, jovian, ones.
Accurate SS Model

4. The SUN rules the SOLAR SYSTEM
Eight major planets with nearly circular orbits
Most have moons, some very large
All orbit the Sun moving in the same direction
Pluto is smaller than the major planets and has a more elliptical orbit: with Eris, Ceres, “dwarf planets”
Lots of asteroids and comets -- space debris; not much mass in them, though.
Mass of Sun: 21030 kg
Radius of Sun: 7105 km
Luminosity: 41026 Watts
Surface temperature: 5760 K

5. Planetary Orbits
Planets all orbit in same direction and nearly in same plane
Martian Orbit Applet
Jovian Orbit Applet
Pluto orbit applet

6. 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.

7. 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.

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 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: interiors, surfaces, atmospheres
We can understand how planets formed and evolved better by comparing them
The possibility of life elsewhere in our solar system or in other solar systems can be considered sensibly via comparisons
Start here on 3/22

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

11. Some Major Features of the Sun and Planets
Sun and planets to scale

12. Sun Over 99.9% of solar system’s mass: 1.9891030 kg
These slides follow the planetary tour pages in ch. 7.
Over 99.9% of solar system’s mass: 1.9891030 kg
Made mostly of H/He ionized gas (plasma); radius: 6.96105 km
Converts 4 million tons of mass into energy each second; powered by FUSION: 4 1H  4He + energy ; luminosity: 3.861026 W

13. Mercury Metal and rock; large iron core but tiny: 0.38 RE, 0.055 ME
Desolate, cratered; long, tall, steep cliffs; no real atmosphere
Very hot/very cold: 425°C (day), –170°C (night) at 0.39 AU
Tides lock it into 3:2 resonance -- 3 sidereal days = 2 years

14. Venus
Nearly identical in size to Earth (0.95 RE); surface hidden by clouds
Hellish conditions due to an extreme greenhouse effect:
Even hotter than Mercury: 470°C, day and night at 0.72 AU
Were (are?) active volcanos; pressure of CO2 atm about 92 times ours

15. Earth Earth and its surprisingly large Moon to scale
Average T = 17 C (290 K); modest greenhouse effect
The only surface liquid water in the solar system
An oasis for life: only O2 rich atmosphere
Plate tectonics recycle the earth’s crust
Significant magnetic field from liquid iron part of core

16. Mars Looks almost Earth-like, but 0.53 radius and 0.107 mass
A very thin, CO2 dominated atmosphere: T = 220 K at 1.52 AU
Giant volcanoes, a huge canyon, polar caps, more…
Water flowed in distant past; could there have been life?

17. Jupiter Much farther from Sun than inner planets: 5.2 AU
Mostly H/He; no solid surface
318 times more massive than Earth
11.2 times its radius
Many moons, 4 very large, + rings
125 K, generates some of its own heat
Very fast winds & big storms in atmosphere

18. Jupiter’s moons Io (shown here): active volcanoes (sulfurous) all over
Are as interesting as some planets themselves, especially Jupiter’s four big Galilean moons
Io (shown here): active volcanoes (sulfurous) all over
Europa: very likely subsurface ocean
Ganymede: largest moon in the entire solar system
Callisto: a large, cratered “ice ball”

19. Saturn Giant and gaseous like Jupiter: 9.46 RE, 95.2 ME
At 9.54 AU and T = 95 K (lots of 95s here!)
Spectacular rings
Many moons, including big cloudy Titan with hydrocarbon lakes

20. All Jovian Planets Have Rings & Moons
Rings are NOT solid; they are made of many small chunks of ice and rock, each orbiting like a tiny moon.
Artist’s conception

21. Current Robotic Mission to Saturn: Cassini
Starte here on 10/13/09:
Inset art shows the Huygens probe separated from the main spacecraft on its descent to Titan…
Cassini mission arrived at Saturn in July 2004 (Launched in 1997)
The Huygens probe landed on Titan in January 2005

22. Uranus
Smaller than Jupiter/Saturn; much larger than Earth: RE & 14.5 ME
Made of H/He gas & hydrogen compounds (H2O, NH3, CH4)
Extreme axis tilt -- nearly on its side, so very long seasons, 60 K at 19.2 AU
Moons & rings

23. Neptune Similar to Uranus (except for axis tilt) but bluer
3.81 RE and 17.1 ME
30.1 AU and T=58K
Many moons too (including big, retrograde orbiting 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.)

24. Pluto and other Dwarf Planets
Much smaller than major planets: round via gravity but don’t dominate orbital zone. (Pluto: 0.18 RE and ME)
Icy, comet-like composition -- smaller than our Moon
Pluto’s main moon (Charon) is of similar size
Pluto at 39.5 AU, Eris at 67.7 AU is a bit bigger

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

26. 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

27. 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

28. General Features of the Solar System
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

29. Simplest Take-Away Points
The major features of the Sun and planets
Sun: Over 99.9% of the mass: provides light and heat
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

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

31. Motion of Large Bodies
All large bodies in the solar system orbit the sun in the same direction and in nearly the same plane (ecliptic)
Most also rotate in that “prograde” direction with modest tilts (<30o)
Conservation of angular momentum

32. Two Main Planet Types
Terrestrial planets are made of rocks & metals, are relatively small, and close to the Sun
Jovian planets are gaseous, mostly H2 and He, much larger, and farther from Sun

33. Swarms of Smaller Bodies Too
Many rocky asteroids and icy comets populate the solar system
Most asteroids are in a “belt” between Mars and Jupiter
Inner comets are in the Kuiper belt beyond Neptune
Comet cores are now mostly in the huge Oort cloud

34. Notable Exceptions
Several exceptions to the normal patterns need to be explained
Earth’s big Moon
Uranus’ sideways tilt
Venus’ (& technically Uranus’) retrograde spins
Triton’s retrograde orbit around Neptune

35. How did we finally learn the physical scale (1 AU = 1
How did we finally learn the physical scale (1 AU = 1.496108km) of the solar system?
Edmund Halley suggested using parallax during transits of Venus in 1710
Tried in 1761 & 1769 and w/ photographs in 1874 and 1882

36. Transit of Venus
Apparent position of Venus on Sun during transit depends on distances in solar system and your position on Earth
Carefully measure times when transit starts and stops at different latitudes
Transit of Venus: June 8, 2004

37. Measuring Distance to Venus
Measure apparent position of Venus on Sun from two locations on Earth
Earth’s radius is known so baseline on earth is known
Use trigonometry to determine Venus’ distance from the distance between the two locations on Earth
We know Venus’s orbit is at AU so we can get the value of an AU

38. Summary of Key System Features
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.

39. Spacecraft Exploration of the Solar System
Spacecraft are essentially robots with computers, rockets, cameras, & other instruments (spectrometers, magnetometers)
Four Basic classes:
Flybys (cheap), but fleeting -- mostly quick pix
Orbiters (need more fuel to brake & enter orbit) but can make much longer observations
Landers (really expensive & big risk of crash) but detailed measurements on the ground (or in atm)
Sample return missions (most expensive: so far only manned Apollo & robotic Luna missions to the Moon)

40. How do robotic spacecraft get there?
Often use a “gravitational slingshot” from a planet instead of fuel whenever possible to accelerate and change direction
Of course rockets needed to get to earth’s escape velocity of 11.2 km/s
Start here on 3/24/10

41. Flybys A flyby mission flies by a planet just once
Cheaper than other mission types but have less time to gather data
Voyagers 1 & 2 to outer planets
Messenger to Mercury (as of 2009; will go into orbit)

42. Orbiters Go into orbit around another world in our Solar System
More time to gather data but cannot obtain really detailed information about world’s surface; for example:
Magellan orbit mapped Venus surface w/ radar in 1990
Mars Reconnaissance Orbiter took incredibly good photos of martian surface starting in 2006
Mars Express studies climate, geology (ESA, 2004)
Galileo went around Jupiter & its moons (1995; sent probe into Jupiter’s atmosphere)
Cassini orbits Saturn & its moons (2004; ESA’s Huygens probe to Titan)
Chandrayaan (ISRO, 2008) and Lunar Reconnaissance Orbiter (2008) are recent missions orbiting the Moon

43. Probes or Landers
Land on surface of another world (e.g. Spirit & Opportunity Rovers on Mars in 2004)
Explore surface in detail with photos, mechanical & chemical analyses
Surveyors to Moon, Veneras to Venus, Vikings to Mars in 1960s and 1970s are original landers; Galileo probed Jupiter
Hayabusa (JAXA) landed on asteroid Itokawa in 2005
LCROSS hit the Moon on 10 Oct 2009

44. Sample Return Missions
Land on surface of another world
Gather samples by hand or claw
Spacecraft designed to blast off other world and return to Earth
The analysis of samples can be done in the most sophisticated way back on Earth -- and saved for superior methods to be used at later times
Last 6 successful Apollo missions to Moon between 1969 and 1972 (and 2 unmanned Soviet Lunas in 1970 & 1976) are the only sample return missions so far
if one exempts Stardust, which brought back material from the tail of Comet Wild 2 in 2006