Satellites of the outer solar system

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Satellites of the outer solar system

• The almost-planets

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Large Moons
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Galilean Satellites
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Interiors
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Surfaces
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Io
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Io Glowing in the Dark...

• Galileo images show glowing gases, hot volcanos,
  in Jupiters shadow
• Volcanic glow suggests volcanos are too hot to be
  ordinary basalt magma

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Eruptions
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Europa
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100 x 140 km
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32 x 42 km
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1.7 x 4 km

• Eroded appearance at highest resolution Few
  impact craters

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Ganymede
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Voyager 2 terrain types on Ganymede cratered
and grooved
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79 x 57 km

• Intense faulting in grooved terrain

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• But some young areas are very smooth
• Surface age 3.5 b.y. or 1.0 b.y.?

54 x 90 km
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• Cratered terrain also complex

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Callisto

• Multi-ring basins
• Bright fresh craters
• Many, many, other craters.

1400 km across
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• Zooming in on Callisto

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• Big surprise at high resolution
• Eroded appearance
• Few small craters

55 x 44 km
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• Dark material between craters is very smooth at
  small scales-
• Why? Sublimation?

13 x 13 km
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Comparative planetology
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Surface Processes

• Io
• Volcanism (endogenic)
• No craters (young surface)
• Europa
• Tectonics (endogenic)
• Cryovolcanism (endogenic)
• Few craters (young surface)
• Ganymede
• Tectonics (endogenic)
• Some craters (older surface)
• Callisto
• Mostly Craters (very old surface)

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Energy

• Recall, for endogenic processes to occur energy
  is needed.
• However, the Galilean satellites are small, so
  they have little internal heat (original or
  radioactive). They are far from the Sun, so get
  little solar energy. Where does the energy come
  from?

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Tidal Heating
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Titan
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Titan

• Titans surface will be revealed with radar
  mapping by the Cassini spacecraft
• Its atmosphere will be measured with the Huygens
  probe
• Its thick atmosphere harbors complex chemical
  reactions
• For this reason, it is interesting to study as an
  early-earth analog and it may harbor life
• The surface may consist of large ethane seas

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Triton
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Triton

• Triton is in a retrograde motion. This implies
  it was captured. Combine this fact with their
  compositional similarities and Plutos uniqueness
  leads some to postulate a similar origin for the
  two bodies.
• The existence of an atmosphere on Triton can be
  seen in the wind streaks on the surface
• Tritons surface is relatively young, there are
  few craters.

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Prometheus
Thalassa
Larissa
Janus
Proteus
Despina
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Small Satellites

• The remaining outer planet satellites are small
  bodies of rock and ice
• They have little internal heating and little
  endogenic activity
• Because of their old surfaces, they are generally
  heavily cratered

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Small Satellites some are quirky

• Mimass large crater Hershel was almost enough to
  shatter the small moon
• Iapetus is two-faced with a dark leading
  hemisphere (3 reflectivity) and a bright
  trailing hemisphere (50)
• Mirandas surface is extensively modified with
  great valley systems (10 km deep) and peculiar
  trapezoidal mountain ranges

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Comparative Planetology 2

• In general, the bigger a planetary body is, the
  more energy is available to modify it
• Small bodies are irregularly shaped and covered
  only with craters (exogenic)
• Slightly bigger bodies are spherical
• Bigger bodies are spherical and differentiated
• The largest bodies are spherical, differentiated,
  and have endogenic processes which modify their
  surfaces