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GEOL 3045: Planetary Geology

GEOL 3045: Planetary Geology. Lysa Chizmadia Uranus. Introduction. 3rd largest planet Seventh from Sun (or eighth) 1st discovered in modern times 1781 by William Herschel Eccentricity = 0.046 18 - 20 AU Axial Tilt = 97.9º Earth = 23.5º Orbital period = 84.1 years

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GEOL 3045: Planetary Geology

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  1. GEOL 3045: Planetary Geology Lysa Chizmadia Uranus

  2. Introduction • 3rd largest planet • Seventh from Sun (or eighth) • 1st discovered in modern times • 1781 by William Herschel • Eccentricity = 0.046 • 18 - 20 AU • Axial Tilt = 97.9º • Earth = 23.5º • Orbital period = 84.1 years • Each pole 42 years continuous Sun, then dark • Rotational period = 17.9 hours • Mass = 8.69 x 1025 kg • ~14.5 Earths • Average  = 1.29 g/cm3 •  = 5.52 g/cm3 (2nd lowest  in solar system) • At least 27 moons Image from: http://www.solarviews.com/eng/uranus.htm Image from: http://en.wikipedia.org/wiki/Uranus

  3. Internal Structure • Atmosphere: • Pressure: 1.2 bars • Earth: ~ 1 bar • Outer 20% of radius • ~0.5 Earth masses • ~83% H, ~15% He & 2% CH4 • Blue color due to absorption of red light by methane • Icy mantle • ~13.4 x Earth masses • Hot dense fluid • Composition: H2O, NH3, etc. • High electrical conductivity • Rocky Core: • ~0.55 x Earth masses •  ~ 9 g/cm3 • P ~ 8 Mbars • T ~ 5000 K Image from: http://www.solarviews.com/eng/uranus.htm

  4. Atmosphere • Structure: • Troposphere • Highly complex cloud structure • H2O clouds • NH4HS clouds • NH3 or H2S clouds • CH4 • Responsible for Far IR emissions • T ~ 59 K • Stratosphere • Contains H-Cs formed from UV radiation of CH4 • May be responsible for bland appearance • Thermosphere/Corona • H2 and H • Extends 2 Uranus radii (~8 Earth radii) False color showing banding Images from: http://en.wikipedia.org/wiki/Uranus

  5. Dark Spot Climate White Storm • At equator, winds retrograde • 50-100 m/s • Wind speeds  to 60 lat • 150-200 m/s • Towards poles, winds prograde • At poles, winds fall to 0 m/s • Dark spots common on Neptune never observed on Uranus until 2006 Images from: http://en.wikipedia.org/wiki/Uranus

  6. Inner Rings Rings • Dark ring system • 2nd discovered • At least 13 distinct rings • Opacity & gaps indicate recent formation • Probably from shattered satellite False color to show structure Fine Structure Shepherd Satellites Images from: http://www.solarviews.com/eng/uranus.htm Images from: http://en.wikipedia.org/wiki/Uranus

  7. Magnetic Field • ~50 x Earth’s magnetic field • Tilted 59 from rotation axis • Not centered with planet • ~1/3 towards south pole • Therefore, highly asymmetric • Strength in S ~0.1 G • Strength in N ~1.1 G • ~ Neptune • May be generated in CH4-H2O ocean instead of in core Image from: http://en.wikipedia.org/wiki/Uranus

  8. Heat Output • Coldest of giant planets • 49 K (~ same as Pluto) • Neptune radiates 2.6 x more heat than receives from Sun • Uranus radiates almost none • Heat flux < Earth • Hypotheses: • When knocked over, lost primordial heat • Barrier in atmosphere prevents heat from reaching space Image from: http://en.wikipedia.org/wiki/Uranus

  9. Summary • 1st discovered in modern times • 2nd least dense planet • Internal structure • Atmosphere • Icy mantle (hot, dense liquid) • Rocky core • Rotates on side • Probably due to massive collision • Complex atmospheric structure • Troposphere • Stratosphere • Thermosphere/Corona • Asymmetrical magnetic field • Coldest of giant planets Image from: http://en.wikipedia.org/wiki/Uranus

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