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Lecture 14

Lecture 14. Outline. Course Evaluations Neptune and Uranus Pluto Kuiper Belt 10-minute break Discuss Exam 3 and Final Final review. Course Evaluations. Course Title = ASTR 111 Section 002. Instructor’s name = Weigel You do not need to fill in questions 23-25

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Lecture 14

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  1. Lecture 14

  2. Outline • Course Evaluations • Neptune and Uranus • Pluto • Kuiper Belt • 10-minute break • Discuss Exam 3 and Final • Final review

  3. Course Evaluations • Course Title = ASTR 111 Section 002. • Instructor’s name = Weigel • You do not need to fill in questions 23-25 • Please take time to answer questions on back: • What aspects of the course and the way it was taught helped you to learn? • What modifications do you suggest for the next time this course is taught? • What did you like/dislike about this course?

  4. Suggested Reading • Chapter 14, all sections • I will post a practice quiz that will not count for credit

  5. Doubling the Solar System

  6. How can you tell the difference between a planet and a distant star? • (assume the both span the same angular distance) • Name two objects in the sky that are not stars

  7. Uranus • Hershel “discovered” it

  8. Neptune’s discovery • A triumph of modern science

  9. The Pioneer anomaly • Is history repeating itself?

  10. 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?

  11. Neptune • Galileo missed it

  12. Atmosphere

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

  14. Bizarro tilt on Uranus

  15. 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

  16. Triggering of Storms

  17. Will Uranus always be tilted?

  18. 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?

  19. “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?

  20. 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

  21. They should not exist

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

  23. 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

  24. Moons and Rings • un14vi03.mov

  25. Uranus and Neptune each have a system of thin, dark rings

  26. Discovery of Uranian Rings

  27. Some of Uranus’s satellites show evidence of past tidal heating Uranus has five satellites similar to the moderate-sized moons of Saturn, plus at least 22 more small satellites

  28. Heavily cratered • Dramatic topography • Unfinished tidal heating?

  29. Triton is a frigid, icy world with a young surface and a tenuous atmosphere • Neptune has 13 satellites, one of which (Triton) is comparable in size to our Moon or the Galilean satellites of Jupiter • Triton has a young, icy surface indicative of tectonic activity • The energy for this activity may have been provided by tidal heating that occurred when Triton was captured by Neptune’s gravity into a retrograde orbit • Triton has a tenuous nitrogen atmosphere

  30. Pluto

  31. Pluto: Problem “Planet”

  32. We almost had 12 planets • “a planet is any body that orbits a star, is neither a star nor a satellite of a planet, and has gravity strong enough to pull it into a rounded shape” • … and “a planet must be heavy enough to clear other objects from its path” http://www.space.com/scienceastronomy/060819_new_proposal.html

  33. Pluto: Problem “Planet”

  34. Pluto and its moon, Charon, may be typical of a thousand icy objects that orbit far from the Sun • Pluto was discovered after a long search • Pluto and its moon, Charon, move together in a highly elliptical orbit steeply inclined to the plane of the ecliptic • They are the only worlds in the solar system not yet visited by spacecraft

  35. Several hundred small, icy worlds have been discovered beyond Neptune • Pluto and Charon are part of this population

  36. Other Objects

  37. A search for a planet between Mars and Jupiter led to the discovery of asteroids • Astronomers first discovered the asteroids while searching for a “missing planet” • Thousands of asteroids with diameters ranging from a few kilometers up to 1000 kilometers orbit within the asteroid belt between the orbits of Mars and Jupiter

  38. Terminology • Asteroid – minor planet or planetoid. Orbit Sun. “Generally bigger than Meteoroid”. • Meteoroid - "A solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule." • Meteor – “shooing star”. Occurs when Meteoroid enters the Earth’s atmosphere • Meteorite – Meteor that survived descent through atmosphere

  39. Asteroids are found outside the asteroid belt—and have struck the Earth • Some asteroids, called near-Earth objects, move in elliptical orbits that cross the orbits of Mars and Earth • If such an asteroid strikes the Earth, it forms an impact crater whose diameter depends on both the mass and the speed of the asteroid

  40. What are chances of hitting asteroid as you pass through asteroid belt?

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