Oceans on Europa The Case for a SubSurface Ocean

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Oceans on Europa?The Case for a Sub-Surface Ocean
Dr. Matthew Burger Department of
Astronomy Burger_at_virginia.edu
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Who Cares About Oceans?

• An ocean on Europa would be the only place
  outside the Earth known to currently have liquid
  water.
• In order to sustain life, we need
• Liquid water
• A strong energy source
• Organic molecules
• Organics are are found in the comets which crash
  into Europa
• An ocean would satisfy the liquid water and
  energy requirements
• So Europa is one of the best places to look for
  current life outside the Earth

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Outline

• Introduction to Jupiters satellites
• Tidal Heating Melting the ice
• So, is there an ocean?
• Finding out once and for all

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The Galilean Satellites
Ganymede
Callisto
Io
Europa
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All of Jupiter's Satellites
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Creating an Ocean Tidal Heating
Gravitational force on a satellite depends on
distance from the primary body.
Each side of a satellite experiences a (slightly)
different force.
This distorts the shape of the satellite.
If the satellite is in a circular orbit and the
same side always faces the planet, then the tidal
bulge does not move on the satellites surface.
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Creating an Ocean Tidal Heating
If the satellite is in an elliptical orbit, the
bulge would get larger and smaller because the
tidal force depends on 1/R3.
As the bulge moves, heat is generated and the
orbit circularizes.
If two satellites are in a resonance, than the
outer one will give the inner one a small kick
each orbit. The planet will constantly try to
circularize the orbit.
?Heat is constantly generated in the inner
satellite.
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Does this actually happen anywhere?
Yes at Io
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But, at Europa the tidal heating is much
less.Why do we think there might be
something going on?
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Europa and Ganymede are in a Resonance
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Europa Has a Young Surface
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Far Side of the Moon
Callisto
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Europas Effect on Jupiters Magnetic Field

• Galileo observations provide compelling evidence
  of the presence of a global scale conducting
  shell capable of carrying a substantial
  electrical current and located within 100 km of
  the surface Kivelson et al 2004
• The easiest way to explain this is a salty,
  liquid ocean beneath the ice

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Europas (Probable) Structure
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What Else Can We Look For?

• Look at the composition of Europas atmosphere
  and surface
• Trace species (sodium, sulfur, organics) may have
  come from the ocean

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Proving the Case A Spacecraft to Europa

• The top priority for a (non-Mars) large-scale
  mission objective is the intensive exporation of
  potential sub-surface oceans on Jupiters icy
  satellites.
• Scientific Goals for the Jupiter Icy Moons
  Orbiter (JIMO)
• Determination of the geological history and
  composition
• Determination of the interior structure and
  evolution
• Study the astrobiological potential
• Investigations of aspects of the broad Jupiter
  system as they relate to the icy satellites

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