1. The Jovian Planets
Chapter 7

2. Topics Jupter, Saturn, Uranus, Neptune How do we know? Why do we care?
What is common about the outer planets?
What is peculiar to each of these planets?

3. Jovian planets (Jupiter-like)

4. Size
radius is about 1/10 of the radius of the Sun

5. Distance from the Sun
Jovian
Terrestrial

6. Terrestrial Jovian Size orbit at 0.4 to 1.5 AU orbit at 5 to 30 AU few
small--1/100 radius of the Sun
large --1/10 radius of the Sun
Size
orbit at 0.4 to 1.5 AU
orbit at 5 to 30 AU
Location
Moons
few
many (# growing)
none
all have rings
Rings
Composition
rocks and metals
gasses and ice

7. Composition 0.71 to 1.67 g/cm3 So what are they made of?
mostly gasses (hydrogen, helium) and ice

8. Jupiter largest planet Great Red Spot
studied by Pioneer, Voyager 1 & 2, Galileo spacecraft
liquid interior (very high pressure and temperature)
16 moons (4 largest are the Galilean moons)

9. Io
Active volcanoes

10. Europa
subsurface ocean
cracked ice

11. Ganymeade
lots of faults
strong magnetic field

12. Callisto
old surface (meaning that it’s not undergoing lots of change except for impact craters)

13. Saturn Large, thin rings
Rings are held together by the gravitational attraction of “shepharding” satellites
Major Gaps: The Cassini and Enke divisions

14. Titan larger than Mercury has an atmosphere
probably has oceans of methane

15. Uranus discovered in 1781 shows no cloud banding
axis of rotation is only tilted 8 degrees from the ecliptic
84 year orbital period
rings originally discovered during occultation of a star
young rings (what’s the source of dust?)

16. Neptune noted by Galileo
the exact path of Uranus could not be explained by the gravitational pulls of the Sun, and the other planets. What does this mean?
discovered in 1846
164 year orbital period
strong magnetic field

17. Triton density 2.1 g/cm3 atmosphere (nitrogen)
impact craters due to comets
ice made of water
active ice volcanoes
retrograde orbit (it’s going the wrong way)
probably captured by Neptune

18. Extrasolar planets
How many planets have we discovered besides those in our solar system?
I’m starting to lose count, but it’s now over 100.
Planets are even found in binary star systems.
We analyze the wobble in a star by studying the Doppler shift in its spectrum and determine the approximate masses and distances of the orbiting planets.

19. How do we know?
How do we know that the outer planets are mostly gas and mostly made up of hydrogen and helium?
How do we know that the atmosphere of a planet has methane?
How do we know the period of rotation of the outer planets? (Note: we use a different technique of measuring rotational period of the terrestrial planets.)
How do we know that a moon’s surface is ice?
How do we know the size of matter within the rings?
How do we know that a moon has an “old” surface and that the moon has little geologic activity?