Lecture 14

2. Lecture 14

4. Outline For Rest of Semester • Oct. 29th Chapter 9 (Earth) • Nov 3rd and 5th Chapter 9 and Chapter 10 (Earth and Moon) • Nov. 10th and 12th Mars, Venus, and Mercury • Nov. 17th and 19th Jupiter and Saturn • Nov 24th Uranus and Neptune • Nov 26th Thanksgiving • Dec. 1st - Exam 3 • Dec. 3rd – Pluto, and the Kuiper Belt • Dec. 8th and 10th – Chapter 7 and 8 (Comparative Planetology I and II) • Tuesday December 15th (7:30 am – 10:15 am) Final Exam • No Reading days are scheduled this semester. (Exam Periodbegins at 7:30 a.m. on Monday, December 14 and ends on December 21)

5. Outline • Quiz discussion • Review question • Neptune and Uranus

6. Roche limit Some of the small shepherd satellites within Saturn's ring system are also inside Saturn's Roche Limit. Why are they not torn apart by tidal forces due to Saturn's gravity?1. The Roche Limit applies only to the ring particles, not to anything as large as a satellite2. The interaction between Saturn's strong magnetic field and the magnetic fields generated by the shepherd satellites helps to hold the satellites together.3. The Roche Limit only applies to objects held together by mutual gravitational attraction, not to chunks of rock like the shepherd satellites.4. Unlike the ring particles, the satellites are large enough to produce significant gravitational fields of their own, and these counteract the tidal forces.

7. Opposition Which planet will appear more often at opposition, Jupiter or Saturn?1. Same2. Jupiter3. Saturn

8. In-class quiz • 15 quiz points for any answer • Triple points if all answers today correct

9. Earth, Moon, Sun, Venus, and Mars

10. Register for quiz 3 Text to 41411: astr111 3 rweigel You will receive either one or two texts in response Replace with your GMU email name

11. Register for quiz 3 Separate group member names with hyphen Text to 41411: astr111 3 rweigel-jsmith1-hjones7 You will receive either one or two texts in response Late students may not work in group

12. 3 1 c 3 1 b 3 1 a 3 1 d Which case, blue, red, green, or black, best represents the configuration in the photo? If you think the black dots best represent configuration in photo, text 3 1 d

13. 3 1 c 3 1 b 3 1 a 3 1 d Which case, blue, red, green, or black, best represents the configuration in the photo? If you think the black dots best represent configuration in photo, text 3 1 d

14. 3 2 d 3 2 b 3 2 c 3 2 a Where is the best placement of moon?

15. d b c a

16. Suggested Reading • Chapters on Uranus and Neptune

17. Neptune and Uranus

18. Doubling the Solar System

19. How can you tell the difference between a planet and a distant star? (assume the both span the same angular distance) • Planet always moves in retrograde • Star always appears at same position in sky • Star position repeats after one year, planet does not • Planet position repeats after on year, star does not 3 3 3 3 3 3 3 3

20. Uranus • Hershel “discovered” it A Short History of Nearly Everything By Bill Bryson (Travel Writer and Humorist)

21. Neptune’s discovery • A triumph of modern science + =

22. The Pioneer anomaly • Is history repeating itself? Pioneer plaque

23. http://www.guardian.co.uk/science/2004/sep/12/spaceexploration.researchhttp://www.guardian.co.uk/science/2004/sep/12/spaceexploration.research • Some researchers say unseen 'dark matter' may permeate the universe and that this is affecting the Pioneers' passage. Others say flaws in our understanding of the laws of gravity best explain the crafts' wayward behaviour. • As a result, scientists are to press a European Space Agency (Esa) meeting, called Cosmic Visions, in Paris this week for backing for a mission that would follow the Pioneers and pinpoint the cause of their erratic movements.

24. The reasons for the anomaly have caused a rift among physicists, … 'Unless there is really good evidence to the contrary, we should stick to simple ideas like these and not go around blaming strange new types of particle or flaws in general relativity,' said Professor Martin Barstow, of Leicester University. • One proposal put forward is that Newton's idea that the force of gravity weakens as distance increases may be incorrect over very large spaces, and may drop off over very long distances.

25. Neptune • Galileo missed it – noted something that star seemed to have moved in relation to other stars. Yo-hoo Over here

26. Neptune’s orbit • Uranus is at about 20 AU and Neptune is at about 30 AU. The ratio is 3:2. Does this mean anything?

27. Neptune’s orbit • Uranus is at about 20 AU and Neptune is at about 30 AU. The ratio is 3:2. Does this mean anything? • Saturn’s orbit is 9.5 AU, Jupiter’s orbit is at 5.2 AU. • Mercury is at 0.38 AU, Venus is at 0.73 AU, Earth is at 1 AU, Mars is at 1.5 AU.

30. Atmosphere

31. Both Uranus and Neptune have atmospheres composed primarily of hydrogen, helium, and a few percent methane • What colors does methane absorb?

32. What colors does methane absorb? • Methane is a greenhouse gas • Greenhouse gasses tend to absorb long wavelength photons, which Earth’s surface emits • Is the color of Uranus consistent with this?

33. Methane is a greenhouse gas • Greenhouse gasses tend to absorb long wavelength photons, which Earth’s surface emits • Is the color of Uranus consistent with this? • Red has long wavelength, blue short. • So methane absorbing long wavelength photons is consistent with it being a greenhouse gas

34. Bizarro tilt on Uranus

35. Exaggerated Seasons On Uranus • Uranus’s axis of rotation lies nearly in the plane of its orbit, producing greatly exaggerated seasonal changes on the planet • This unusual orientation may be the result of a collision with a planetlike object early in the history of our solar system. Such a collision could have knocked Uranus on its side

37. Which would you guess has a more active atmosphere? • Based on distance from Sun • Based on above pictures

38. Neptune looks more active • But its orbit is 30 AU compared to 20 AU for Uranus. What is the difference between amount of energy they receive?

39. “Thanks to distance, Neptune receives less than one-half of the amount of solar energy than Uranus.” • Where did the “one-half” number come from?

40. “Thanks to distance, Neptune receives less than one-half of the amount of solar energy than Uranus.” • Where did the “one-half” number come from? • Energy Flux ~ 1/r2 • Energy Flux Uranus ~ 1/202 = 1/400 • Energy Flux Neptune ~ 1/302 = 1/900 • Ratio is 400/900, which is a little less than 0.5

41. Interior

42. Uranus and Neptune contain a higher proportionof heavy elements than Jupiter and Saturn • Both Uranus and Neptune may have a rocky core surrounded by a mantle of water and ammonia • Electric currents in the mantles may generate the magnetic fields of the planets

43. They should not exist

44. Bizarro Magnetic Axis The magnetic fields of both Uranus and Neptuneare oriented at unusual angles

45. The magnetic axes of both Uranus and Neptune are steeply inclined from their axes of rotation • The magnetic and rotational axes of all the other planets are more nearly parallel • The magnetic fields of Uranus and Neptune are also offset from the centers of the planets

46. Moons and Rings • un14vi03.mov Movie 16.3

47. Uranus and Neptune each have a system of thin, dark rings Movie 16.3

48. Discovery of Uranian Rings

49. Movie Movie 16.2