1. 1 “A Post Galileo view of Io’s Interior” Keszthelyi et al. Icarus 169 (2004) Raquel Fraga-Encinas Dec 7, 2004UMD TERPS Conference

2. 2 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

3. 3 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)

4. 4 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

5. 5 Modeling MELTS numerical thermodynamic model from published data Assume Pressure ~ 100Mbar Upper mantle ~ 50% molten, core boundary 10-20%

6. 6 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

7. 7 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

8. 8 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)

9. 9 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

10. 10