JUPITER: King of the Planets

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JOVIAN (GAS GIANT) PLANETS
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SATURN

• Nearly as big as Jupiter, and it rings very
  nicely.
• Cassini image of Saturn, edge-on rings, their
  shadows,
• moons Dione Enceladus

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SATURN Ringed and Very Gassy

• Mass is 95.2 times that of Earth.
• Radius is 60,268 km or 9.45 times Earth's.
  Density is only 0.687 g/cm3 or 0.125 of Earth's.
• The most distant naked eye planet.
• Period of 29.42 years.
  Semi-major axis, a 9.54 AU,
  e 0.054. Inclination to ecliptic 2.49 deg
• 9 moons discovered from the ground.
• No solid surface differential rotation
  Magnetic (interior) spin period 10h 40m
  Spins so fast is so gassy that its
  ellipticity gt 10 axial tilt 26.7 deg

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Rings and Orbit
Rings are prominent tilted at 27 degrees so seen
from different angles from Earth nearly
invisible when edge-on
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Saturn's Atmosphere and Interior are Very Similar
to Jupiter's

• BUT the main interior differences include
• Lower density less mass so less compression and
  relatively more gaseous
• Molecular H2 layer ? 30,000 km thick Metallic
  H layer ? 15,000 km thick Rocky/metallic core, R
  ? 15,000 km
• Central T 15,000 K P 5 x 106 atm
• Strong magnetic field, but still only 5 of
  Jupiter's.

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Saturns Interior
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Saturns Atmospheric Differences from Jupiter

• Fewer belts and zones (due to lower T) but faster
  winds (to 1500 km/h) Thicker cloud
  layers (lower gravity) Less
  coloration (probably due to lower T)
• In atm H2 over 92, He almost 8 Why?
• He has settled or rained downwards.
  At the lower T and P of Saturn's atm,
  He doesn't dissolve in H2 Separation of He
  and compression of whole planet yields much more
  heat, so Saturn's surface T is 97 K, not 74 K.

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Saturns Atmosphere

• Real color from HST showing storm near equator
  and pole at earlier time.
• False color image from IR blue, haze free
  green, more haze orange, high clouds

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Atmospheric Structure and Fast Winds
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URANUS and NEPTUNE

• Most Distant Official Planets are NEARLY TWINS
• MU 14.54 M? MN 17.15 M? .
• RU 25,559 km or 4.01 times Earth's.
• RN 24,766 km or 3.88 times Earth's.
• ?U 1.27 g cm-3 ?N 1.64 g cm-3 .

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As seen from Earth, URANUS

• Discovered by Wm. Herschel in 1781 (barely
  visible to naked eye, greenish, nearly
  featureless)
• Period of 83.75 years
• Semi-major axis 19.19 AU, e 0.047
• 5 moons discovered from the ground pre-space 10
  by Voyager, 2 more by 200-inch.
• Tilted by 98 deg ? LONG seasons
• Magnetic (interior) spin period 17.2 h
  (retrograde)

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Seasons on Uranus

• Axis almost in orbital plane so equatorial zones
  have two summers near equinoxes and two winters
  near solstices poles have 42 yr of light and 42
  years of dark

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Rotation on Uranus

• HST shows cloud motions over 8 hours
• IR HST picture shows clouds and rings

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As seen from Earth, NEPTUNE

• Predicted by John Adams (1845) and Urbain
  Leverrier (1846) producing growing error in
  Uranus's position noticed over the years
• Found in the right place by Johann Galle in Sept.
  1846 -- bluish, tiny disk Voyager showed some
  bands
• P163.7 yr a 30.07 AU e0.009
• 2 moons discovered from the ground 11 from space
• Magnetic (interior) spin period 16.1 h surface
  17.3 h

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ATMOSPHERES

• Temperatures Uranus, 58 K Neptune 59 K
• Both Uranus and Neptune are about 84 H2 and 14
  He.
• Methane (CH4 ) is most of the remainder
  Methane absorbs red light, so planet looks
  blueish/green More CH4 in Neptune, so it's bluer
  Ammonia is frozen out in
  these very cold atmospheres
• No internal heat source for Uranus, so washed out
  bands and zones covered by a haze. Fairly
  strong winds distribute Sun's heat so sunny side
  isn't much hotter than shady side.
• Neptune has an internal heat source probably
  extra methane has helped to trap internal heat of
  formation ?more noticeable bands and some storms

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Neptunes Dark Spot (from Voyager) and
Cloudsfrom IR HSTviews showing brightening as
more sunlight hits South side
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Interiors of Uranus and Neptune

• Below atmospheres, each about 1/3 of R
• MOLECULAR HYDROGEN (unlikely to convert to metal)
• below that, SLUSH, including water ice and
  dissolved ammonia an electrically conducting
  fluid
• ROCKY CORE (maybe 10 M? )

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Magnetic Fields

• Despite not having (much) metallic hydrogen both
  have substantial internal fields (100 times
  earth's, 1/10th Saturn)
• Off-center and misaligned with spin axis (60O for
  Uranus, 46O for Neptune, vs. 10O for Jupiter and
  well-aligned for Saturn).
• Why? currently reversing reflecting a blow
  ionic NH3 ?