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The Smaller Giants and Pluto

The Smaller Giants and Pluto. Uranus and Neptune And Poor Pluto!. Uranus Personification of Heaven and ruler of the World. Uranus. First telescopic planet: by William Herschel on 13 March 1781 Added one planet to six, but doubled the size of the Solar System!

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The Smaller Giants and 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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