1. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Saturn

2. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 The Spectacular Saturn System

3. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Mass: 5.7 × 10 26 kg Radius: 60,000 km Density: 700 kg/m 3 – less than water! Rotation: rapid and differential, enough to flatten Saturn considerably Rings: very prominent; wide but extremely thin

4. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Saturn’s atmosphere is similar to Jupiter’s, except the pressure is lower Three cloud layers Cloud layers and the haze layer are deeper than Jupiter’s and more dense

5. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Like Jupiter Saturn has stripes and differential rotation. They are much more subdued and are rarely seen through Saturn’s haze and cloud cover. Jupiter-style “spots” are rare on Saturn. They don’t form as often and quickly dissipate if they do

6. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Saturn’s Interior

7. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Saturn also has a strong magnetic field, but only about 5% as strong as Jupiter’s. It has Van Allen Belts where charged particles from the Solar Wind are trapped and they produce aurorae.

8. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Historically, only one ring was seen. As our instruments got better we were able to distinguish more detail. The rings are labeled by letter in the order of their discovery.

9. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Ring particles range in size from fractions of a millimeter to tens of meters They are made of dust and rock covered with water ice Why rings? They are too close to planet for moon to form – tidal forces would tear it apart

10. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Closest distance that a moon could survive is called the Roche limit; planetary ring systems are all inside this limit

11. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 The Voyager probes showed Saturn’s rings to be much more complex than originally thought The Earth is shown on the same scale as the rings

12. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 The Cassini division turns out not to be completely empty. The gap seems to be caused by an orbital resonance with other ring particles and Saturn’s innermost moon

13. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Voyager also found radial “spokes” that formed and then dissipated; this probably happens frequently

14. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 It was expected that sharp edges and divisions in the Rings would be caused by ‘Shepherd Moons’. It was not so. The other edges and divisions in the rings now seem to be the result of resonance. However, a “Shepherd” moon does define the outer edge of the [A] ring through gravitational interactions.

15. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Strangest ring is the F ring. It appears to have braids and kinks. F ring’s oddities are probably caused by’ two ‘Shepherd Moons’, one of which can be seen here

16. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Details of ring formation are unknown It is thought that rings are too active to have lasted since the birth of the solar system Either they must be continually replenished, or they are the result of a catastrophic events

17. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Saturn’s many moons appear to be made of water ice or carbon based rocks covered with ice Besides the small moons, Saturn has: Six medium-sized moons (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus) One large moon (Titan) which is almost as large as Ganymede

18. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Saturn’s many moons appear to be made of water ice or carbon based rocks covered with ice. There are six medium-sized moons and one large moon (Titan) which is almost as large as Ganymede

19. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Titan has an atmosphere thicker and denser than Earth’s. It is made mostly of nitrogen and argon but it also has some very interesting chemistry in its upper atmosphere. The surface can NOT be seen through the haze. This image was taken by Voyager I from only 4000 km away

20. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 After Voyager there was much desire to learn more about Titan and the Saturn system. The Cassini Orbiter and the Huygens Probe were sent to make that Study. This artist’s impression is of Cassini as the Huygens Probe was released.

21. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 The Huygens Probe analyzed the atmosphere of Titan as it descended. Many trace chemicals mostly derived from methane make the atmosphere chemically complex.

22. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 During its descent Huygens photographed the surface below. Here we see a shore line of a lake and a watershed feature that looks like a river system. The liquid is not water but liquid methane. The light colored patches seem to be methane frost or snow,

23. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 On 9/16/05 Huygens landed on a slushy area dotted with boulders composed of water ice, under orange clouds composed of complex hydrocarbons

24. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Mimas, Enceladus, Tethys, Dione, and Rhea all orbit between 3 and 9 planetary radii from Saturn, and all are tidally locked – this means they have “leading” and “trailing” surfaces. Iapetus orbits 59 radii away, and is also tidally locked The medium sized moons are shown on scale with the Earth’s Moon

25. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Rhea, the largest, has a highly reflective, heavily cratered surface. The wispy features are on the trailing side but not the leading; their origin is not yet fully understood.

26. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Dione and Tethys are similar, having icy, heavily cratered surfaces

27. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 Mimas is the closest moon to Saturn, and has a crater covering one-third of its surface, the result of an impact that must have almost destroyed the moon Iapetus is two-faced: its leading side is very dark (reflects 3% of incoming light), while its trailing side is bright (reflects 50% of incoming light).

28. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 This moon possesses a region of terrain near its south pole that is dramatically devoid of impact sites. Scientists suspected it is geologically active. The discovery in 2009 of material jetting from the pole and creating a great plume of icy particles confirmed these suspicions. The Cassini continues to study it because it seems to have liquid water inside. Enceladus orbits close to Mimas, but is very shiny, indicating a surface covered with ice crystals

29. Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com Chapter 12 End of Chapter 12