Ground-based observations of time variability in multiple active volcanoes on Io

Since before the beginning of the Galileo spacecraft’s Jupiter orbital tour, we have observed Io from the ground using NASA’s Infrared Telescope Facility (IRTF). We obtained images of Io in reflected sunlight and in-eclipse at 2.3, 3.5, and 4.8 μm. In addition, we have measured the 3.5 μm brightness of an eclipsed Io as it is occulted by Jupiter. These lightcurves enable us to measure the brightness and one-dimensional location of active volcanoes on the surface. During the Galileo era, two volcanoes were observed to be regularly active: Loki and either Kanehekili and/or Janus. At least 12 other active volcanoes were observed for shorter periods of time, including one distinguishable in images that include reflected sunlight. These data can be used to compare volcano types and test volcano eruption models, such as the lava lake model for Loki.