Investigating Astronomy Timothy F. Slater, Roger A. Freeman

1. Investigating AstronomyTimothy F. Slater, Roger A. Freeman Chapter 7 Observing the Dynamic Giant Planets

2. Observing Jupiter and Saturn • The disk of Jupiter at opposition appears about two times larger than the disk of Saturn at opposition, which is about two times farther away. • Both planets display dark and light bands, though these are fainter on Saturn. (As viewed from on the Earth)

3. Observing Jupiter and Saturn As viewed from Voyager space probe

4. Solid Rotation versus Differential Rotation • All parts of a solid object rotate together. • A rotating fluid displays differential rotation.

5. The Compositions of Jupiter and Saturn • An outer core of liquid “ices” • A layer of helium and liquid metallic hydrogen • A layer of helium and ordinary molecular hydrogen (H2) • Saturn has more rocky core and less liquid

6. Jupiter’s Atmosphere

7. Jupiter’s Bands This visible-light image of Jupiter was made by the Voyager 1 spacecraft. Bright and dark areas in this Earth-based infrared image, taken at the same time, correspond to high and low temperatures, respectively.

8. Jupiter and Saturn’s Cloud Layers • The black curves show temperature versus altitude in each atmosphere, as well as the probable arrangements of the cloud layers. • Beneath both planets’ cloud layers, the atmosphere is composed almost entirely of hydrogen and helium. • (Zero altitude = 1/10 of Earth’s atmospheric pressure.)

9. ConceptCheck: • Will Jupiter’s rocky moons, such as Ganymede, exhibit differential rotation? • If Jupiter and Saturn formed with nearly the same chemical composition, why might Jupiter be observed to have more helium than Saturn? • Besides color, what is the difference between Jupiter’s white ovals and brown ovals? • Why might Jupiter’s cloud layers be more compressed than Saturn’s?

10. Uranus’s Atmosphere • Faint cloud markings became visible in images of Uranus only after extreme computer enhancement. • The color is due to methane in the planet’s atmosphere, which absorbs red light but reflects green and blue. • The substances that make up the clouds on Jupiter and Saturn are not available on Uranus.

11. Neptune is a cold, bluish world withJupiter-like atmospheric features. • Neptune has essentially the same atmospheric composition as Uranus • Receives half the energy from the Sun as Uranus • Continued contraction fuels Neptune’s storms?

12. Frozen Storms and Methane Clouds • Like wispy, high-altitude cirrus clouds in the Earth’s atmosphere, these clouds are thought to be made of ice crystals. • The difference is that Neptune’s cirrus clouds are probably methane ice, not water ice.

13. Internal Structures of Uranus and Neptune Both Uranus and Neptune have • a rocky core, resembling a terrestrial planet • a mantle of liquid water with ammonia dissolved in it • an outer layer of liquid molecular hydrogen and liquid helium

14. ConceptCheck: • If methane were absent from Uranus’s atmosphere, what color would it appear? • Why would scientists be surprised that Neptune had active belts and zones, unlike Uranus?

15. Saturn’s Moon Titan • Titan has a thick atmosphere with a unique chemical composition. • The haze surrounding Titan is so dense that little sunlight penetrates to the ground. • Titan could have methane rain and lakes of liquid ethane!

16. Seeing Titan’s Surface • Visible/ infrared imagery • Titan’s rocks are chunks of water ice.

17. Neptune’s Moon Triton • A conspicuous absence of large craters―Triton has a young surface on which the scars of ancient impacts have largely been erased by tectonic activity. • Areas that resemble frozen lakes and may be the calderas of extinct ice volcanoes. • A dimpled, wrinkled terrain that resembles the skin of a cantaloupe.

18. ConceptCheck: • Prior to the Huygens probe, why was so little known about the surface of Titan? • How was an atmosphere detected on Triton?

19. Saturn’s System of Rings • Saturn is visible through the rings, which shows that the rings are not solid. • The C ring is so faint that it is almost invisible in this view.

20. The Changing Views of Saturn’s Rings • Saturn’s rings are tilted 27° from Saturn’s orbital plane. • As Saturn orbits, observers on Earth see the rings at various angles. • The rings seem to disappear when viewed edge-on.

21. Nature of Rings • Saturn’s rings are made of unconnected “moonlets,” or ring particles, each individually circling Saturn. • Astronomers have long suspected that the ring particles are made of ice and ice-coated rock. • Ancient debris that failed to accrete into moons or objects that were pulled apart when they came too close to Saturn.

22. Color Variations in Saturn’s Rings • Cassini images show the rings innatural color. • Color variations are indicative of slight differences in chemical composition among particles in different parts of the rings.

23. The Arrangement of Saturn’s Rings • The location of Saturn’s rings along with the orbits of the 11 inner satellites. • Only the A, B, and C rings can readily be seen from the Earth. • The remaining rings are very faint, and their existence was only confirmed by spacecraft flybys.

24. Dim Ring Systems Around Jupiter,Neptune, and Uranus

25. Seeing Dim Rings

26. ConceptCheck: • What causes Saturn’s brilliant rings to be sometimes nearly invisible and at other times easily observable with the smallest of telescopes? • If an asteroid entered a low-Earth orbit inside Earth’s Roche limit, what would become of it? • Why are Saturn’s rings easier to observe than those of the other planets?

27. Next Chapter: Chapter 8 Looking for Life Beyond Earth