Uranus in the Sky

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Uranus in the Sky
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Uranus
As seen by Voyager
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Uranus Highlights

• Accidently discovered in March 1781 by William
  Herschel
• Fits Bodes Law!
• Visited by Voyager 2 in 1986
• Suspicious lack of internal heat probably leads
  to bland appearance of atmosphere
• Composition 75 H, 25 he
• Probably a small rocky core (3 of total mass)
• Ice-rock slush interior
• Bluish color derives from methane which is a good
  absorber of red light

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Discovery of Uranus

• William Herschel at right discovered Uranus by
  accident. He used the 6-inch telescope at right,
  which he built himself.

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Featureless Planet
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Atmosphere of Uranus
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Interior View of Uranus and Neptune
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Oddball Properties of Uranus

• Magnetic field
• About same Earths field
• BUT, dipole inclined by 60o and offset from
  planet center by 1/3 of RU
• Caught during a field reversal???
• Tilt
• Extreme tilt remains unexplained
• Each pole spends 42 years in light and then 42 in
  darkness

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The Odd Magnetic Field of Uranus
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Rings of Uranus

• Discovered March 1977 during a stellar
  occultation
• Nine narrow rings ranging in width 10-100 km
• Thin and faint with particles of size cm to
  several meters
• Dust fills inter-ring gaps
• Requires replenishment
• Moons Cordelia and Ophelia act to shepherd some
  rings

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Ring Discovery from Occultation
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Uranus Ring System
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The IR View
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Discovery of Neptune

• By 1821, the orbit of Uranus clearly deviated
  from its predicted path which couldnt be
  explained by influence of known planets.
• Evidence for another planet!
• Discovered by Adams (English, late 1845) and
  Leverrier (France, 1846) independently
• 1st observed by Galle (German) on 9/23/1846

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Neptune
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Scale of Neptune
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Voyager at Neptune
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Neptune with Moons
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Neptunes Atmosphere

• Belts
• Zones
• Clouds
• Wind - 2200kph at the equator
• Storms - ovals and Great Dark Spot
• Great Dark Spot
• High pressure region in S. hemisphere, about size
  of Earth
• By 1994, Spot had disappeared, and a new Dark
  Spot had formed at N. latitudes (HST)

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Multi-Wavelength Neptune
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Cloud Decks at Neptune
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Neptunes Great Dark Spot
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Neptunian Weather
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Neptunes Magnetic Field

• Surface field similar to Earths in strength
• Magnetic axis tilted by 47o
• Dipole offset by 1/2 RN
• Unlikely that both Uranus and Neptune are
  undergoing field reversals at the same time!

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Summary of Magnetic Fields
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Internal Energy of Neptune

• Uranus lacks convection and therefore storms
• Neptune does have internal heat like Jupiter and
  Saturn (Neptune emits 60 more than absorbs)
• A MYSTERY!
• How can Uranus and Neptune be so different
  when so similar in size and mass?
• Inhibition of convection in Uranus?

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Rings of Neptune

• Voyager 2 found rings, although there had been
  previous evidence for them
• Dark and faint
• Little intergap dust
• Rings likely composed of dust themselves
• Bright arcs in out ring (effect of shepherding?)

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Rings of Neptune