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A Post Galileo view of Ios Interior

• Keszthelyi et al. Icarus 169 (2004)
• Raquel Fraga-Encinas
• Dec 7 , 2004 UMD TERPS Conference

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View right after Voyager flybys

• Completely molten interior (Peale 1979)
• Thin lithosphere flexed by tidal forces causes
  tidal heating
• Underlying basaltic magmas drive up sulfur
  eruptions

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View right before Galileo flybys

• Thick cold lithosphere (gt 30km)
• Aesthenospheric heating model (Ross et al. 1990)
• Ios interior considered largely solid (Nash et
  al. 1986)

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Galileo Mission Observations

• SSI (0.41 um) , NIMS (0.7-5.2 um), PPR
  (visible-100 um) Timeline1995-2003
• Pillan Patera eruption T 1870 /- 25 K
• SSI color data hottest spots were darkest near
  1 micron presence of enstatite
• Limits superheating due to rapid ascent or tidal
  heating of materials

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Modeling

• MELTS numerical thermodynamic model from
  published data
• Assume Pressure 100Mbar
• Upper mantle 50 molten , core boundary 10-20

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Post-Galileo View Io Implications

• Core molten Fe-S mix , size 550-900 km
• Mantle molten 10 base to 50 upper
  (enstatite composition)
• Crust at least 13km thick (continually recycled
  into mantle)
• Can explain features like paterae plumes

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Concluding remarks

• This latter model is closer to what was proposed
  on the 70s than prior to the Galileo mission
• Uncertainties on lava temperatures? Need more
  data

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RIGHT Si magma (red) rises thru rock, not
buoyant enough to reach volatiles (navy). Heat
melts S (yellow) and SO2 (light blue) when it
vaporizes erupts into surface. Depression forms
and can be unroofed forming the patera. LEFT
Orange (warm S) black spot (Si unroofed)
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L/LL-chondrites have low Fe content, have olivine
pyroxene IO INFO Mass 8.94E25 g Radius
1821 km Av. Density 3.53 g/cc
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