The History of Volcanic Eruptions on Io

Broad band infrared radiometry between 4.8 and 20 mu m collected at the NASA Infrared Telescope facility has been used to characterize Io's thermal emission from volcanic activity. Data has been collected since 1983 through the present, allowing us to put the current activity during Galileo's tour into a historic perspective. We have modeled the light curve data using 6 volcanic centers. Areas and temperatures of spots were fitted by calculating the flux at 4.8, 8.7, and 20 m and matching the flux to the orbital light curves. Current trends in volcanic activity indicate the high temperature portion of Loki is at a low level of activity compared to the monitoring record. The modeled high temperature areas for Loki are equivalent to a circular region with a radius of 5 km and a temperature of 550 K in July, 1996. Conversely, high temperature activity in the Pele hemisphere increased in 1995 and is still at high levels. Emission from the Pele region in 1993 were below our detection level. In 1995, Pele was modeled as a circular region 12 km in radius with a temperature of 500 K. In July 1996, this had increased somewhat to a circular region 15 km in radius with a temperature of 500 K. This work was done at JPL/ CALTECH, under contract to NASA. Also all authors were visiting scientists at the NASA Infrared Telescope Facility.