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Trans-Neptunian Objects and Pluto

Trans-Neptunian Objects and Pluto. Astronomy 311 Professor Lee Carkner Lecture 21. Trans-Neptunian Region. Beyond Neptune is the region of small, icy, Trans-Neptunian Objects

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Trans-Neptunian Objects and Pluto

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  1. Trans-Neptunian Objects and Pluto Astronomy 311 Professor Lee Carkner Lecture 21

  2. Trans-Neptunian Region • Beyond Neptune is the region of small, icy, Trans-Neptunian Objects • The region is populated by icy planetesimals that either formed at the edge of the solar system or were ejected out by the planets

  3. Pluto -- God of the Underworld • Pluto is the God of the Dead in Roman mythology

  4. The Discovery of Pluto • In the late 1800’s it was believed that Neptune’s orbit was being perturbed by a 9th planet • In 1930 a young astronomer named Clyde Tombaugh found a very faint planet near Lowell’s predicted position

  5. The Discovery of Pluto

  6. Observing Pluto • Through most telescopes Pluto simply appears as a faint star

  7. Pluto Facts • Size: 2300 km • Orbit: 39.5 AU • Description:

  8. Pluto’s Orbit • Pluto’s orbit is much more eccentric and much more inclined than any planet • Pluto’s orbit carries it inside the orbit of Neptune • Pluto is tipped on its side like Uranus

  9. Composition of Pluto • Pluto has a density of 2000 kg/m3 • Pluto is probably composed of ice and rock • Spectra of Pluto reveal the presence of methane, nitrogen and carbon monoxide

  10. HST Images Pluto

  11. Features of Pluto • The other bright regions may be areas where impacts have gouged out fresh ice

  12. Pluto and Charon

  13. Charon • Pluto’s moon Charon was discovered as a small bulge in a high resolution image (1978) • Pluto and Charon are in a close, tidally locked orbit

  14. Where Do Comets Come From? • Comets are small (few km) icy bodies that sometimes come in to the inner solar system on highly elliptical orbits • Short period comets • Long period comets

  15. The Kuiper Belt • Around 1950 Kuiper and Edgeworth proposed a belt of comets out beyond Neptune • In 1992 the first (besides Pluto) Kuiper belt object was discovered (QB1)

  16. The Kuiper Belt

  17. Discovering Kuiper Belt Objects

  18. The Known Kuiper Belt • There are now hundreds of known Kuiper Belt Objects (KBOs) • Total population of large KBO’s may be 70000 (larger than 100 km) • Kuiper belt seems to end at about 50 AU • Larger and larger KBO’s being detected

  19. Eris • The largest KBO currently known is called Eris • Larger than Pluto • Semi-major axis of 68 AU, but is currently at 97 AU due to high eccentricity • Has a small moon, Dysnomia

  20. Large KBO Size Comparisons

  21. Pro Con Is Pluto a Planet?

  22. What Makes Something a Planet? • Planets used to be obvious • Needed new definition when rest of solar system was discovered with telescopes • The International Astronomical Union (which has authority over these things) removed Pluto from the list of planets in 2006

  23. The Oort Cloud • In 1950 Dutch astronomer Jan Oort postulated a spherical shell of comets surrounding the solar system at about 50,000 AU

  24. Population of the Oort Cloud • The Oort cloud is the source of the long period comets • They are too far away to see, so we only have indirect methods of studying them

  25. Diagram of the Oort Cloud

  26. Summary • Past the orbit of Neptune the solar system is made up of many small icy bodies • Kuiper Belt • extends from 30-500 AU • formed from left over planetesimals at the edge of the solar system • Oort Cloud • extends from 1000-100,000 AU • formed from ejected icy planetesimals

  27. Summary: Pluto • Description: small, cold , distant • Pluto resembles a large Kuiper belt object more than a planet • Has a closely orbiting large moon Charon • Properties • Thin atmosphere • Very cold (~50 K) • Bright surface features possibly composed of fresher ice

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