At the time of this writing the superbly instrumented Galileo spacecraft is approaching Jupiter. Galileo is expected to establish the definitive reference data set for Io. Undoubtedly, a variety of new volcanic phenomena will be revealed. Thus, we will not have to wait long before there will be another improvement in our understanding of Io. Since many of the processes involved in Jovian-system's tidal interactions and in the resurfacing of Io have long time scales, continuing ground-based observations of Io's volcanic activity will be worth doing long after the end of the Galileo mission. Examples of such observational programs include images from the Hubble Space Telescope [e.g. Sartorettti et al., 1994] and earth-based infrared observations [e.g. Spencer et al., 1992, 1990; Veeder et al., 1994] and occasional, special viewing opportunities such as the 1991 mutual occultations and eclipses of the Galilean satellites [e.g. Spencer et al. 1994] will allow continued monitoring of Io's volcanic activity during and beyond Galileo era.
Acknowledgments. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract from NASA.