HR: 1340h
AN: V33C-1476    [Abstracts]
TI: Galileo SSI Observations of High Temperature Lavas on Io: Improved Error Analysis and Implications for the Interior
AU: * Keszthelyi, L
EM: laz@usgs.gov
AF: USGS, Astrogeology Team, Flagstaff, AZ 86001 United States
AU: Milazzo, M
EM: mmilazzo@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AU: Jaeger, W
EM: jaeger@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AB: The SSI camera onboard the Galileo spacecraft captured images of incandescent lava on Jupiter's moon Io between 1997 and 2001 at 17 m/pixel to 20 km/pixel. Previous estimates of lava temperature have come from combining the SSI 0.4-1.0 micron data with NIMS mid-infrared data and numerical cooling models. These model results indicated an eruption temperature of $\sim$1600 $\deg$C, implying ultramafic compositions. Improved error analysis of the SSI data improves our brightness, color, and eruption temperature estimates. At Tvashtar Catena we obtained a brightness temperature of 1100 $\deg$C for an active curtain of lava in November of 1999. From the height of the fountains, we estimate the ballistic flight time for the pyroclasts to be $\sim$1 minute. This implies an eruption temperature $\sim$1700 $\deg$C, if the fountain is optically thick. We also find that the hottest pixels from the February 2000 lava flow in Tvashtar Catena had a color temperature of about 1400 $\deg$C. If these pixels contained lava with a wide range of ages, it would imply an eruption temperature approaching 2500 $\deg$C. Alternatively, we suggest that the entire 10$^{5}$ m$^{2}$ area of these pixels contains no lava more than a few seconds old. This allows an eruption temperature of 1600-1700 $\deg$C. These very high lava temperatures are difficult to reconcile with models for the interior of Io. The high temperatures suggest almost complete melting of the mantle. However, the ultramafic crust would be gravitationally unstable over a largely liquid mantle and it would be difficult to generate the tidal heating to drive the observed volcanism. We investigate superheating via viscous dissipation within ascending magma as a possible explanation. If the mantle is largely solid, the expected magma source region temperature is about 1200 $\deg$C, so we require about 500 $\deg$C of superheating. This could be provided if the driving pressure on the magma is about 3 GPa. For buoyancy to provide this driving pressure, the magma needs to be rising from a depth of $>$10$^{4}$ km. The radius of Io is only 1820 km. We conclude that we do not yet understand how Io can have these very hot lavas.
DE: 8414 Eruption mechanisms
DE: 8439 Physics and chemistry of magma bodies
DE: 5480 Volcanism (8450)
DE: 6218 Jovian satellites
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting