Ground-based observations of volcanism on Io in 1999 and early 2000

Ground-based observations of volcanism on Io during the period of the 1999 and early 2000 Galileo close flybys have detected several types of activity, providing information which complements the spacecraft observations. At Loki a brightening began between August 25 and September 9 and continued through February. On August 2 a major outburst was observed near (14°N, 74°W) whose brightness corresponds to an area of approximately 350 km² at a temperature of 1100 K. Observations of eruptions in late June (9906A) and in late November (9911A, at Tvashtar) provide temporal and photometric constraints on activity also seen by Galileo. High-resolution adaptive optics images provide further information on the fainter sources distributed across the surface.