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Neptune and Uranus: Doubling the Solar System

Explore the fascinating characteristics of Neptune and Uranus, including their discovery, atmospheric composition, unusual orbits, magnetic fields, and intriguing moons. Discover how these planets challenge our understanding of the solar system.

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Neptune and Uranus: Doubling the Solar System

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  1. Lecture 23

  2. Outline • Neptune and Uranus

  3. Neptune and Uranus

  4. Doubling the Solar System

  5. 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

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

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

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

  9. 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.

  10. 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.

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

  12. 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?

  13. 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.

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

  15. 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?

  16. Bizarro tilt on Uranus

  17. 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

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

  19. 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?

  20. “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?

  21. 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

  22. They should not exist

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

  24. 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

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

  26. 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

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

  28. 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

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