IOS THERMAL ANOMALIES - CLUES TO THEIR ORIGINS FROM COMPARISON OF GROUND-BASED OBSERVATIONS BETWEEN 1 AND 20 MU-M

Io's thermal emission for 1995 from eclipse photometry at 2.2 mu m; br oad band radiometry at 4.8 mu m, 8.7 mu m and 20 mu m; and in eclipse imaging between 1.7 and 5 mu m are compared. The variability of therma l emission from Io at wavelengths between 1-5 mu m (Silverstone et al. , 1995; Spencer er al., 1997) is in agreement with the expected variab ility based on the 13 year record presented in Veeder at al. (1994) an d Goguen et al. (1996). We conclude that 1995 was typical for Io, in t erms of overall observed variability in the volcanic sources. Detailed comparison of data from Goguen et al. on Aug. 24 and Spencer et al. o n Aug. 26 provides evidence of a high temperature eruption that produc ed a larger, cooler region over the course of two days. The observed f requency of occurrence of high temperature events, the linking of high and lower temperature thermal anomalies, and the observed stability o f volcanic regions since Voyager suggests that high temperature silica te eruptions could support the entire observed population of cooler te mperature anomalies. It may be more productive to consider sulfur flow s on Io in the context of remobilization of existing sulfur deposits.