Moons of the Jovian Planets: Satellites of Ice and Rock

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Moons of the Jovian Planets Satellites of Ice
and Rock

• What kinds of moons orbit the jovian planets?
• What makes Jupiters Galilean moons unusual?
• What makes Saturn's moon Titan different from
  other moons?
• Why are small icy moons more geologically active
  than small rocky planets?

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What kind of moons orbit the jovian planets?

• Two kinds
• Medium and large moons
  mostly formed at the same time as their
  planets (nearly circular orbits, all in the same
  direction).
• Small moons
  mostly captured asteroids and comets
  (mildly to extremely elliptical orbits, even
  retrograde ones).

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Medium large moons

• Lots of ice
• Active resurfacing in the past (some moons even
  today)
• Enough self-gravity to be spherical young,
  molten' moon rock and ice ran downhill' like
  water on Earth until it made a sphere on which
  there is no more downhill'

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What makes Jupiters Galilean moons unusual?
IO EUROPA Ganymede
Callisto
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Ios Volcanoes

• Io is the solar system's most volcanic world.

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Tidal stress cracks Europas surface ice, which
floats to new positions on a subsurface ocean of
water or slush.
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Interiors of Io Europa are warmed by tidal
heating.
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What makes Saturn's moon Titan different from
other moons?
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What makes Saturn's moon Titan different from
other moons?

• Only moon with an atmosphere 90 nitrogen, plus
  argon, methane, hydrocarbons (smog!).
• Methane ethane are greenhouse gases.
• Still cold 93 K (-180 degrees C)
• Chemical reactions on Titan produce organic,
  chemicals (hydrocarbons, etc.)
• Cassini spacecraft images show a young surface
  (few craters) but with evidence of hydrocarbon
  lakes only at the poles.

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Neptunes Moon Triton

• Possibly a captured Kuiper belt object orbiting
  Neptune opposite Neptunes direction of rotation
• Neptune's tidal bulges (caused by Triton) are
  pulling backwards on Triton, slowing it down into
  a future crash into Neptune.
• Smaller than Earths Moon, yet has recent
  geological activity (nitrogen geysers).

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Uranus small moon Miranda shows huge cliffs
tectonic activity, and few craters.
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Why are small icy moons more geologically active
than small rocky planets?

• Hot interiors needed for geological activity.
• Ice deforms more easily than solid rock
• Less internal heat is required
• Smaller objects can be geologically active.
• Tidal heating important for some icy moons, but
  not for rocky planets (example the Moon's tides
  are slowing down the Earth, but not heating it up
  by any significant amount).

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What have we learned?

• What kinds of moons orbit the jovian planets?
• We can categorize the more than 100 known moons
  as small, medium-size, or large.
• Most medium-size and large moons probably formed
  with their planet in the disks of gas that
  surrounded the young jovian planets.
• Small moons are most often captured asteroids or
  comets.

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What have we learned?

• What makes Jupiters Galilean moons unusual?
• Io is the most volcanically active object in the
  solar system. Europa may have a deep, liquid
  water ocean under its icy crust. Ganymede also
  thought to have a subsurface ocean.
• What makes Titan different from other moons?
• Titan is the only moon in our solar system with a
  thick atmosphere. It has a young surface with
  lots of contrasting features, but we don't yet
  know what they are.

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What have we learned?

• Why are small icy moons more geologically
  active than small rocky planets?
• Ices deform and melt at much lower temperatures
  than rock, allowing icy volcanism and tectonics
  at surprisingly low temperatures.