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The Mysteries of Uranus, Neptune, and the Quest for Pluto

Explore the fascinating discoveries of Uranus and Neptune, including their unique characteristics and the role of mathematics in their identification. Learn about Uranus's unusual rotation, its bluish hue from methane, and its significant moons and rings. Delve into Neptune's deep blue color, its Great Dark Spot, and its various satellites, especially Triton. Finally, uncover the story of Pluto's discovery, its composition, and the ongoing debate over its planetary status. Join us on this cosmic journey of the smaller giants!

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The Mysteries of Uranus, Neptune, and the Quest for Pluto

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  1. The Smaller Giants and Pluto Uranus and Neptune And Poor Pluto!

  2. Uranus Personification of Heaven and ruler of the World

  3. Uranus • First telescopic planet: by William Herschel on 13 March 1781 • Added one planet to six, but doubled the size of the Solar System! • Mean distance from the Sun ≈ 19.2 AU • Orbital period ≈ 84 years • Rotation period ≈ 17.24 hours • Mean surface temperature ≈ 57 K [–357 °F] • Spin axis tilted sideways: 97.9° to orbital plane

  4. UranusContinued • Radius ≈ 4  REarth • Mass ≈ 14.6  MEarth • Density = Mass÷Volume ≈ 1.3 gm/cm3.Similar to Jupiter’s! • Must contain light substances: water, hydrogen, methane and ammonia. Spectra confirm this. • Composition details from shape and density • Not-very-large core of rock and iron-rich material

  5. UranusContinued • Featureless blue sphere • Blue coloration due to methane that absorbs red light and rejects (scatters) the blue • Faint cloud bands seen in computer-processed images from the Voyagers • Clouds are crystals of frozen methane • Very fast winds (90 – 360 m.p.h.) cause east-to-west bands in cloud features • North-to-south heat transport smears up the bands

  6. UranusContinued • Five major satellites discovered from Earth in 1781 (2), 1851(2), and 1948 • Ten more small ones by Voyager 2 in 1986 • Water ice and compounds of carbon and nitrogen • Most satellites dark in appearance • Have marks of severe impacts • Nine thin, dark rings seen from Earth in 1977; two more found by Voyager 2

  7. Uranus Imaged in the Near-Infrared

  8. The Erratic UranusA Tale of Two Great Detectives • Discovery in 1781 by William Herschel • Old star charts showed it as a star in 19 records from 1690 onwards • Bouvard (circa 1818) tried to calculate orbit • Could use the more complete “ancient” data of unknown accuracy or “modern” ones • Discrepancies were too large either way • Published tables in 1821, based on the modern data

  9. The Erratic UranusThe Detective Story (continued) • Discrepancies in position began to grow, becoming as large as 1/30 of 1°by 1846 • J. C. Adams on 3 July 1841: “Formed a design in the beginning of this week, of investigating, as soon as possible after taking my degree, the irregularities in the motion of Uranus which are yet unaccounted for.” • Calculations of improving accuracy between 1843 – 1845. Ignored by G. B. Airy until quite late. Futile search by Challis.

  10. The Erratic UranusThe Detective Story (continued) • U J J Leverrier independently, and by different mathematics, found the same results in 1845-1846 • Discovery by Johann Galle at Berlin on 23 September 1846. • Great triumph of Newtonian laws which some (notably Airy) were willing to modify • Great international squabble over priority • Might have been seen by Galileo in 1613! Neptune!!!

  11. Neptune - God of the Sea

  12. Neptune • First planet discovered by mathematics • Mean distance from the Sun ≈ 30 AU • Orbital period ≈ 165 years • Rotation period ≈ 16.11 hours • Mean surface temperature ≈ 57 K [–357 °F] • Mass ≈ 17.2  MEarth • Radius ≈ 3.9  REarth • Density = Mass÷Volume ≈ 1.64 gm/cm3

  13. NeptuneContinued • Contains light substances: water, hydrogen, methane and ammonia. Spectra confirm this. • Deep blue because the methane in atmosphere absorbs red light strongly • Atmosphere shows cloud bands and a Great Dark Spot, reminiscent of Jupiter’s Red spot • Atmosphere rotates more slowly than bulk • Too high a percentage of H and He; too little of heavy elements (relative to Jupiter & Saturn)

  14. NeptuneContinued • Thin ring system. Dark in appearance, possibly because methane converted to dark compounds by radiation • Magnetic field tilted at 47° to axis • Has extensive satellite system: 8 • Major moon Triton: • Icy; young surface; tenuous atmosphere • Polar cap of nitrogen frost • Retrograde orbit; spirals inwards

  15. Triton’s southern region, including its south polar ice cap; could be nitrogen ice.

  16. Kuiper-Belt Objects • Beyond orbit of Neptune • Icy objects found • Tens to hundreds of km • Gerard Kuiper • Source of some Comets • TNO

  17. Pluto • Found by methodical search in 1930 (Clyde W. Tombaugh) • Distance from Sun ≈ 40 AU • Radius ≈ 0.2  REarth (1/5) • Mass ≈ 0.002  MEarth (1/500) • Density is about 2 gm/cm3, implying a rocky/icy structure • Spectra show a thin methane atmosphere and methane frost on surface • One relatively large, nearby moonCharonfound in 1978 (James Christy). Very similar to Pluto!

  18. Hubble Space Telescope views of Pluto

  19. Relative Sizes of Pluto and Charon

  20. The End.

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