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AST 101 Lecture 17 Is Pluto a Planet?

AST 101 Lecture 17 Is Pluto a Planet?. Rhea, Enceladus, Dione. Pluto. Discovered 1930 Named the 9 th planet Radius ~ 2330 km In 6 day orbit w/ Charon Pluto system: 6 objects Demoted 2006 Classified a dwarf planet by the IAU

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AST 101 Lecture 17 Is Pluto a Planet?

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  1. AST 101Lecture 17 Is Pluto a Planet?

  2. Rhea, Enceladus, Dione

  3. Pluto • Discovered 1930 • Named the 9th planet • Radius ~ 2330 km • In 6 day orbit w/ Charon • Pluto system: 6 objects • Demoted 2006 • Classified a dwarf planet by the IAU • http://www.thedailyshow.com/watch/wed-january-28-2009/neil-degrasse-tyson Clyde Tombaugh

  4. What is a Planet? • A planet is not a star or browndwarf • It is not massive enough to generate core temperatures that can drive fusion • Maximum mass: 0.013 M, or 13 MJ • Planets orbit stars (must they?) • Planets dominate their orbit • Planets are round. “It all depends on what the meaning of ‘is’ is” William Jefferson Clinton

  5. Sun’s Planets • Earth • Historical planets: (ρλανετ, or wanderer) • Mercury • Venus • Mars • Jupiter • Saturn • Later discoveries • Uranus (1781) • Neptune (1846)

  6. Titius-Bode Law A mathematical relation published by J.E. Bode in 1772 a = (2nx 3 + 4) / 10 • a is the semimajor axis of the orbit in AU • n is an index: • Mercury: -1 (set 2-1 = 0) • Venus: 0 • Earth: 1 • Mars: 2 • Jupiter: 4 • Saturn: 5 a matches observation to within a few %. The Titius-Bode law is empirical: there is no physical reason why it should hold, but it has proven of some use as a predictor

  7. Titius-Bode Law. II a = (2nx 3 + 4) / 10 “Missing” values of n: • 3: corresponds to the distance of Ceres, discovered in 1801 by Piazzi. • 6: corresponds to Uranus • 7: a=40 AU, Neptune is at 30 AU Why does the Titius-Bode Law appear to work? Simulations show planets cannot be too close together. Planetary separations can often be approximated as a geometric series

  8. Characteristics of the Major Planets • Planets orbit in or near the ecliptic. • the greatest inclination to the ecliptic is 7o (Mercury). • Planets have nearly circular orbits. • Excluding Mercury, the largest orbital eccentricity is <10%. • Pluto: • Inclination = 17.1o • Eccentricity = 0.25

  9. What Are Planets Made Of? We can measure planetary densities • Mercury, Venus, Earth, Mars: ρ~5 gm/cm3 • Jupiter, Saturn, Uranus, Neptune: ρ~1 gm/cm3 • Reference densities: • Water, liquids, and ices: ~1 gm/cm3(Sun) • Rock: ~3 gm/cm3 (Moon) • Rock + metal core: ~5 gm/cm3 (Earth) • Degenerate matter: ~106gm/cm3 (white dwarf)

  10. Types of Planets • Terrestrial (rocky) • metal core, rocky mantle • minimal atmosphere • Jovian (gas giants) • rocky/metallic core • substantial atmosphere

  11. Terrestrial Planets

  12. Jovian Planets

  13. Solar System Sizes

  14. Other Bodies • Moon • Ceres, Juno, Pallas, Vesta, and the other 200,000 or so asteroids • Pluto, Charon, and the other TNOs (trans-Neptunian objects)

  15. Moon • Density ~ 3  no metallic core • Remnant of the 5th terrestrial planet?

  16. Minor Planets 1 Ceres R = 457 km 951 Gaspra 19 x 12 x 11 km

  17. Minor Planet 443 Eros 40 x 14 x 14 km NEAR flyby 12/23/98

  18. 2/12/01: NEAR Lands on Eros

  19. Surface of Eros

  20. Trans-Neptunian Objects • 90377 Sedna • a=518 AU e=0.85 Discovered at ~ 90 AU • Radius: 1200-1600 km

  21. 136199 Eris Radius ~ 2330 km - same as Pluto

  22. TNOs, KBOs, and Centaurs

  23. Is Pluto a Planet? • Highly inclined, non-circular orbit • Trapped in resonance with Neptune • Similar to other TNOs • IAU Designations: • 8 major planets • ~40 dwarf planets • Many minor planets

  24. What is Pluto? • King of the Dwarf Planets? • Runt of the Major Planets? Planet X: Christine Lavin

  25. References Much more information on Pluto is available at: • http://nineplanets.org/pluto.html The International Astronomical Union’s view of Pluto: • http://www.iau.org/public/pluto/ The IAU Resolutions: http://www.iau.org/public_press/news/detail/iau0603/

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