Temperature and variability of Pillan, Wayland Patera, and Loki Patera on Io from Cassini ISS data

Cassini spacecraft images of Io obtained during its flyby of Jupiter in late 2000 and early 2001 were used to determine the lava composition and eruption style of three faint hot spots, Pillan, Wayland Patera, and Loki Patera. We found a maximum color temperature of 1130 ± 289 K for Pillan and maximum color temperatures of 1297 ± 289 K and 1387 ± 287 K for Wayland Patera and Loki Patera, respectively. These temperatures are suggestive of basaltic lava but an ultramafic composition cannot be ruled out. The temperatures with the best signal-to-noise ratios also suggested basaltic lava and were found to be 780 ± 189 K, 1116 ± 250 K, and 1017 ± 177 K for Pillan, Wayland Patera, and Loki Patera, respectively. Pillan showed constant thermal output within error over three days of observations. The data also suggest Pillan may be surrounded by topography that blocked emission in the middle of the observation and caused a more dramatic decrease in emission. Wayland Patera’s intensity decreased over the three eclipse observations, consistent with a cooling lava flow or decreasing effusion rate. Intensities at Loki Patera over the course of the observations varied, consistent with previous determinations that Loki Patera is an often quiescent lava lake with periods of overturning, fountaining, and crustal foundering.