The Jovian Planets, Part III

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The Jovian Planets, Part III

• Uranus and Neptune

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URANUSThe God of the Heavens
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Physical Data

• Discovered by William Herschel in 1781
• Diameter 51,118 km (4.01 Dearth)
• Mass 8.69x1025 kg (14.54 Mearth)
• Density 1.24 g/cm3
• Rotation Period 17.24 hours
• Tilt of Axis 98o (retrograde rotation!)
• Surface Temperature 52 K (-366o F)

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Physical Data

• Orbital Semi-Major Axis 19.18 AU
• Orbital Period 84.01 years
• Orbital Inclination 0.8o
• Orbital Eccentricity 0.047
• Surface Gravity 0.919 Earth gravity
• Satellites 15 known
• Magnetic Field yes

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Uranus Interior
MOLECULAR HYDROGEN
ATMOSPHERE


ICE
ROCK
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The Discovery of Uranus

• First discovered planet even though at its
  closest to earth it can be seen with the naked
  eye
• Was recorded 22 times as a star on star charts
  before W. Herschel discovered it as a planet in
  1781

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Uranus Motions
N
S
N
N
SUN
S
S
N
S

• Uranus rotates on its side, producing strange
• seasons and day-night patterns

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Uranus Atmosphere

• COMPOSITION
• 85 Hydrogen
• 15 Helium
• Traces of Methane
• CLOUDS
• Mostly made of methane ice
• Featureless cloudtops (inconspicous bands)

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Uranus Magnetic Field

• Magnetic dipole is offset 31 from the center of
  the planet
• Tilted -59o from rotational axis
• Comparable in strength to Earths (0.74 Earths)
• Uranus has aurora and radio emissions

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Uranus Rings

• Found from star occultations in 1977
• Thought to be made of stone
• Uranus also has partial rings called ring arcs
• Also has sheperd satellites

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Uranus Moons

• All are named after William Shakespeare and
  Alexander Pope characters
• There are 15 known moons

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Uranus Moons

• MIRANDA
• Surface is a weird mix of old and new terrain
• It has been proposed than it was shattered and
  reassembled in this way
• There was not enough heat to fuse it smoothly
  together

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Uranus Moons

• ARIEL
• Youngest surface of the Uranian Satellites
• There is evidence of tectonic activity
• It has faults over 10 km deep

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Uranus Moons

• TITANIA
• Largest of Uranus moons
• Has faults up to 100 km across
• Has a heavily cratered surface

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NEPTUNEGOD OF THE SEA
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Physical Data

• First observed in 1846 by Johann Galle
• Diameter 49,500 km (3.89 Dearth)
• Mass 1.030x1026 kg (17.23 Mearth)
• Density 1.61 g/cm3
• Rotation Period 16.11 hours
• Tilt of Axis 28.76o
• Surface Temperature 57 K (-357o F)

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Physical Data

• Orbital Semi-Major Axis 30.06 AU
• Orbital Period 164.79 years
• Orbital Inclination 1.8o
• Orbital Eccentricity 0.009
• Surface Gravity 1.19 Earths gravity
• Satellites 8 known
• Magnetic Field yes

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The Discovery of Neptune

• Its existence was calculated before it was
  observed from variations of Uranus orbit from
  what was predicted
• Calculations were made by U.J. Leverrier, sent to
  Johann Galle at Berlin Observatory, and he found
  Neptune after searching for 30 minutes
• Galileo actually recorded Neptune twice in 1612
  and 1613 in his notebooks as a background star in
  his drawings of Jupiter

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Neptunes Interior
MOLECULAR HYDROGEN
ATMOSPHERE

ICE
ROCK
Similar to Uranus
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Neptunes Atmosphere

• 75 Hydrogen
• 25 Helium
• Small amounts of Methane, Ammonia
• Acetylene
• There are three majors cloud-top features
• The Great Dark Spot
• Dark Spot 2
• Scooter

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Neptunes Atmosphere

• The Great Dark Spot
• Anti-cyclone with a circulation period of 16 days
• About the size of Earth
• In southern hemisphere

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Neptunes Atmosphere

• Dark Spot 2
• Smaller cyclone in S. hemispere
• Scooter
• Fast rotating
• Rapidly changes shape

Great Dark Spot
Scooter
Dark Spot 2
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Neptunes Magnetic Field

• Magnetic dipole is offset 55 from center of
  Neptune
• Tilted -47o with respect to rotational axis
• Has a field strength of 0.4x Earths at the
  equator
• Has aurora and radio emissions

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Neptunes Rings

• Discovered in 1981
• Brighter areas are ring arcs
• There is a total of 5 rings, all very thin

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Neptunes Moons

• TRITON
• Has thin atmosphere, geysers, and strange
  cantaloupe terrain
• Diameter 3000km

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Neptunes Moons

• Proteus
• Second largest moon of Neptune discovered by
  Voyager
• Surprisingly, Neried, Neptunes third largest
  moon was discovered from the ground before Proteus