1B11 Foundations of Astronomy The Jovian Planets

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1B11 Foundations of AstronomyThe Jovian Planets

• Silvia Zane, Liz Puchnarewicz
• emp_at_mssl.ucl.ac.uk
• www.ucl.ac.uk/webct
• www.mssl.ucl.ac.uk/

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1B11 The Giant Planets
The 4 giants
the icy object Pluto

• Low densities ? mostly H He (ices for Uranus,
  Neptune)
• Surfaces cloud tops
• Magnetic fields all strong (Jupiters mag.
  Moment 20.000 Earths)
• Internal heat J, S, N radiate ? twice the heat
  they receive from the Sun ? internal heat e.g.
  gravitational contraction (? 1mm/year), etc..

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1B11 The Interior
Ex. Jupiter
Based on mean density, assumed chemical
composition. And Hydrogen Phase diagram
T? 165K P? 1 bar
T?10000K P?3 Mbar
Liquid Molecular H ( He)
T?20000K P?70 Mbar
Liquid Metallic H ( He)
15 (Radius) 75
100
? Rocky-ice core10-15 M?
Clouds (complex molecules)
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1B11 The Interior
Ex. Uranus and Neptune
H20 ( He)
Ices (H20 , CH4)
30 (Radius) 75
100
Rocky core?
Same size as rock/ice core of Jupiter and Saturn
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1B11 The Interior
Hydrogen Phase diagram
T(K)
J
S
104
Liquid H2
Liquid Metallic
U, N
103

Solid H2
Solid Metallic
102
0.1
1.0
10
100
P (Mbar)
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1B11 The Surface Layers
Predicted Cloud Structure
0.1 bar
50
NH3
1 bar
0
NH4SH
-50
H2O
10 bar
-100
120
160
340

• These clouds are white. The reds and brown
  observed clouds result from more complex
  hydrocarbons produced by photolysis of NH3, CH4,
  etc..
• Clouds are more muted on Saturn, owing to lower
  UV

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1B11 The Surface Layers
This animation of Jupiter was created from a
mosaic of images taken by the Voyager spacecraft.
As the animation starts, the great red spot is
towards the left side. A number of brown spots
can be seen just above center.

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1B11 Internal Heat
Jupiter, Saturn and Neptune all radiate about
twice as much energy as they receive from the
Sun ? An internal heat source, possible
responsible for dynamic meteorology of Jupiter
Possibilities

• Primordial heat
• Gravitational Contraction (? 1mm/yr)
• Combination of all of these

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1B11 Planetary rings
Moonlet, held together by gravity

• All four giant planets have rings
• Rings are composed of small, solid (generally
  icy) particles orbiting in equatorial plane
• Probable origin disruption of small moons or
  comets within a giant planets Roche limit

Disrupted by tidal forces
R
RP
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1B11 Major Satellites of Jupiter and Saturn
Jupiter (Galilean Satellites, 1610)
Saturn (Titan, 1655)
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1B11 Galilean Satellites Summary
Io

• Highly volcanic
• Energy Source tidal friction

Europa

• icy crust, few craters
• Evidence for ocean

• recent resurfacing (new ice)
• surface features (ice flows)
• spectral evidence for salts
• ? possible biosphere ?

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1B11 Galilean Satellites Summary
Ganimede, Callisto

• Thick icy mantles to keep density low

Heavily cratered icy crust (esp. Callisto)
Silicate mantle

Ice (possibly liquid at depth)
Possible core ? (esp. Ganimede)

• Both probably now inert, Ganymede has been
  active more recently than Callisto (few craters ?
  younger surface)

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1B11 Titan (moon of Saturn)
Atmospheric composition
N2 82 99 CH4 1-6 Ar 1-6
? Many Hydrocarbon traces, e.g. Ethane (C2H6)

• Clouds organic molecules produced by photolysis
• Surface ice? Covered in hydrocarbons, possibly
  liquid?

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1B11 Triton (moon of Neptune)
Composition
Ice/rock? Very thin (105 bar) N2 and CH4
atmosphere

• It has a retrograde orbit ? CAPTURED?
• similar object to Pluto?

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1B11 Pluto (discovered 1930)

• Mean orbital distance 39.5 AU
• Eccentricity 0.25
• Orbital inclination 17.1º
• Radius 1150 km (0.18 R? smaller than
  triton!)
• Mean density 2.0 g cm3 (rock/ice composition)
• Atmosphere very thin (105 bar) N2 with CH4
  (like Triton)
• Moon Charon (radius595 km, orbital period 6.4
  d)

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1B11 Trans-Neptunian objects (TNOs)

• Since 1992 ?200 icy objects with diameters ?100
  km have been found beyond Neptune.
• More than 70000 are thought to exist between 30
  and 50 AU.
• Pluto and Triton are probably just the largest
  and/or the closest members of the TNO population.
• TNOs probably mark the inner edge of the KUIPER
  belt-source of short period comets

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1B11 web sites
http//www.ex.ac.uk/Mirrors/nineplanets http//ww
w.solarviews.com/eng/
Images of planets, missions, moons, rings.. And
links therein!