“A Post Galileo view of Io’s Interior”
Keszthelyi et al. Icarus 169 (2004)
Dec 7 , 2004
Raquel Fraga-Encinas
UMD TERPS Conference
1
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
2
View right before Galileo flybys
• Thick cold lithosphere
(> 30km)
• Aesthenospheric
heating model (Ross et
al. 1990)
• Io’s interior
considered largely
solid (Nash et al. 1986)
3
Galileo Mission Observations
• SSI (0.4–1 um) , NIMS (0.7-5.2 um), PPR
(visible-100 um) Timeline:1995-2003
• 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
4
Modeling
• MELTS numerical thermodynamic model from
published data
• Assume Pressure ~ 100Mbar
• Upper mantle ~ 50% molten , core boundary 10-20%
5
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
6
Concluding remarks
• This latter model is closer to what was proposed
on the 70’s than prior to the Galileo mission
• Uncertainties on lava temperatures? Need more
data
7
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)
8
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
9
10